JP7357752B2 - Magnetic tape, magnetic tape cartridges and magnetic tape devices - Google Patents

Description

The present invention relates to a magnetic tape, a magnetic tape cartridge, and a magnetic tape device.

2. Description of the Related Art Magnetic recording and reproducing devices that record data on a magnetic recording medium and/or read (reproduce) recorded data are broadly classified into magnetic disk devices and magnetic tape devices. A typical example of a magnetic disk device is an HDD (Hard Disk Drive). A magnetic disk device uses a magnetic disk as a magnetic recording medium. On the other hand, magnetic tape devices use magnetic tape as a magnetic recording medium.

In both magnetic disk devices and magnetic tape devices, it is preferable to narrow the recording track width in order to increase the recording capacity (higher capacity). On the other hand, the narrower the recording track width is, the more likely it is that signals from adjacent tracks will be mixed into the signals of the track to be read during playback, making it more difficult to maintain playback quality such as SNR (Signal-to-Noise Ratio). Become. Regarding this point, in recent years, it has been proposed to improve the reproduction quality by reading the signals of the recording track two-dimensionally using a plurality of reading elements (also called "reproduction elements") (for example, Patent Document 1 (See ~3). If the reproduction quality can be improved in this way, the reproduction quality can be maintained even if the recording track width is narrowed, and thus the recording capacity can be increased by narrowing the recording track width.

Japanese Patent Application Publication No. 2016-110680 Japanese Patent Application Publication No. 2011-134372 US Patent No. 7755863

Patent Documents 1 and 2 discuss magnetic disk devices. On the other hand, magnetic tape has recently attracted attention as a data storage medium for storing large amounts of data for long periods of time. However, magnetic tape devices are generally sliding type devices in which data is read (reproduced) by sliding a magnetic tape and a reading element in contact with each other. Therefore, the relative position between the reading element and the track to be read tends to fluctuate during reproduction, and improvement of reproduction quality tends to be more difficult than with magnetic disk devices. Although Patent Document 3 includes a description regarding a magnetic tape device (tape drive), it does not disclose any specific means for improving the playback quality in the magnetic tape device.

An object of one aspect of the present invention is to provide a magnetic tape capable of reproducing data with good reproduction quality in a magnetic tape device that uses a plurality of reading elements (reproducing elements).

One aspect of the present invention is
A magnetic tape having a non-magnetic support and a magnetic layer comprising a ferromagnetic powder and a binder, the magnetic tape comprising:
The magnetic layer has a timing-based servo pattern,
The edge shape specified by magnetic force microscopy observation of the above-mentioned timing-based servo pattern is determined by the value L _99.9 of 99.9% of the cumulative distribution function of the positional deviation width from the ideal shape in the longitudinal direction of the magnetic tape, and the above-mentioned cumulative distribution function. It has a shape in which the difference (L _99.9 - L _0.1 ) from the value L _0.1 of 0.1% is 180 nm or less, and the refractive index Nxy measured in the in-plane direction of the magnetic layer and the above A magnetic tape having an absolute value ΔN of the difference between the refractive index Nz measured in the thickness direction of the magnetic layer (hereinafter also referred to as "ΔN (of the magnetic layer)") of 0.25 or more and 0.40 or less,
Regarding.

In one aspect, Nxy>Nz may be satisfied, and the difference (Nxy−Nz) between the refractive index Nxy and the refractive index Nz may be 0.25 or more and 0.40 or less.

In one aspect, the timing-based servo pattern may be a linear servo pattern that extends continuously from one side to the other in the width direction of the magnetic tape and is inclined at an angle α with respect to the width direction, The ideal shape may be a linear shape extending in the direction of the angle α.

In one aspect, the difference (L _99.9 −L _0.1 ) can be greater than or equal to 100 nm and less than or equal to 180 nm.

In one embodiment, the magnetic tape may have a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.

In one aspect, the magnetic tape may have a back coat layer containing nonmagnetic powder and a binder on the surface side of the nonmagnetic support opposite to the surface side having the magnetic layer.

One aspect of the present invention relates to a magnetic tape cartridge containing the above magnetic tape.

One aspect of the present invention is
magnetic tape and
a reading element unit;
an extraction section;
including;
The magnetic tape is a magnetic tape according to one aspect of the present invention,
The above reading element unit is
comprising a plurality of reading elements each reading data from a specific track area including a track to be read among track areas included in the magnetic tape;
The extraction unit extracts data originating from the read target track from the read results by performing waveform equalization processing on each of the read results for each of the read elements;
Regarding.

In one aspect, each of the plurality of reading elements can read data from a specific track area including a track to be read out of track areas included in the magnetic tape using a linear scan method.

In one aspect, the waveform equalization process may be a waveform equalization process according to an amount of positional deviation between the magnetic tape and the reading element unit.

In one aspect, the waveform equalization process may be performed using a tap coefficient determined according to the amount of shift.

In one embodiment, the amount of deviation may be determined according to a result obtained by the servo element reading a timing-based servo pattern of a magnetic layer of the magnetic tape.

In one aspect, the reading element unit may include a servo element, and a reading operation of the reading element unit may be performed in synchronization with a reading operation performed by the servo element.

In one embodiment, the plurality of reading elements may partially overlap each other in the running direction of the magnetic tape.

In one aspect, the specific track area may be an area including the track to be read and an adjacent track adjacent to the track to be read, and each of the plurality of reading elements may be connected to the magnetic tape. When the positional relationship changes, it is possible to straddle both the track to be read and the adjacent track.

In one embodiment, the plurality of reading elements may be arranged in close proximity to each other in the width direction of the magnetic tape.

In one embodiment, the plurality of reading elements can be accommodated within the track to be read in the width direction of the magnetic tape.

In one aspect, for each of the plurality of reading elements, a ratio of an overlapping area with the track to be read and an overlapping area with an adjacent track adjacent to the track to be read can be specified from the amount of deviation, The tap coefficient may be determined according to the specified ratio.

In one aspect, the extraction unit may include a two-dimensional FIR (Finite Impulse Response) filter, and the two-dimensional FIR filter performs the waveform equalization process on each of the reading results for each reading element. By combining the results obtained by this, data originating from the track to be read can be extracted from the reading results.

In one aspect, the plurality of reading elements can be a pair of reading elements.

According to one aspect of the present invention, it is possible to provide a magnetic tape that can reproduce data with good reproduction quality in a magnetic tape device that uses a plurality of reading elements (reproduction elements). According to one aspect of the present invention, a magnetic tape cartridge including such a magnetic tape can also be provided. Further, according to one aspect of the present invention, it is also possible to provide a magnetic tape device having such a magnetic tape and a plurality of reading elements (reproducing elements).

FIG. 1 is a schematic configuration diagram showing an example of the overall configuration of a magnetic tape device. 1 is a schematic plan view showing an example of a schematic planar configuration of a reading head and a magnetic tape included in a magnetic tape device; FIG. FIG. 2 is a schematic plan view showing an example of a schematic configuration of a reading element unit and a magnetic tape when viewed from above. FIG. 2 is a schematic plan view showing an example of a schematic configuration of a track area and a pair of reading elements when viewed from above; 7 is a graph illustrating an example of the correlation between SNR and track offset for each of single read element data and first composite data under a first condition. 7 is a graph illustrating an example of the correlation between SNR and track offset for each of single read element data and second composite data under a second condition. FIG. 2 is a block diagram illustrating an example of a main configuration of electrical hardware of a magnetic tape device. FIG. 3 is a conceptual diagram for explaining a method of calculating a deviation amount. 3 is a flowchart illustrating an example of the flow of magnetic tape reading processing. FIG. 2 is a conceptual diagram illustrating processing performed by a two-dimensional FIR filter of an extraction unit. FIG. 7 is a schematic plan view showing an example of a state in which the reading element unit straddles the reading target track and the second noise mixing source track. FIG. 7 is a schematic plan view showing a first modification of the reading element unit. FIG. 7 is a schematic plan view showing a second modification of the reading element unit. An example of the arrangement of data bands and servo bands is shown. An example of servo pattern arrangement for LTO (Linear-Tape-Open) Ultrium format tape is shown. FIG. 3 is an explanatory diagram of an angle α regarding the edge shape of a servo pattern. FIG. 3 is an explanatory diagram of an angle α regarding the edge shape of a servo pattern. An example of the edge shape of a servo pattern is shown. An example of a servo pattern is shown. An example of a servo pattern is shown. An example of a servo pattern is shown. FIG. 3 is a conceptual diagram for explaining a first example. FIG. 7 is a conceptual diagram for explaining a second example. FIG. 3 is a diagram showing an example of a two-dimensional image of a reproduced signal obtained from a single reading element.

Below, first, the configuration of a magnetic tape device that uses a plurality of reading elements (reproducing elements) will be explained.

The magnetic tape device can include a magnetic tape, a reading element unit, and an extractor. Regarding reading data from a magnetic tape, in the example shown in FIG. 22, an elongated reading head 200 includes a plurality of reading elements 202 along the longitudinal direction. A plurality of tracks 206 are formed on the magnetic tape 204. The reading head 200 is arranged so that its longitudinal direction coincides with the width direction of the magnetic tape 204. Further, each of the plurality of reading elements 202 is assigned to each of the plurality of tracks 206 in a one-to-one relationship, and reads data from the tracks 206 at opposing positions.

However, the magnetic tape 204 typically expands and contracts due to changes in time, environment, tension, and the like. When the magnetic tape 204 expands and contracts in the width direction, the centers of the reading elements 202 arranged at both longitudinal ends of the reading head 200 shift from the center of the track 206 . When the magnetic tape 204 is deformed by expanding and contracting in the width direction, the closer the read elements 202 to both ends of the read head 200 are, the more affected by off-track the read elements 202 are. In order to reduce the influence of off-track, for example, it is possible to provide a margin for the width of the track 206. However, as the width of the track 206 increases, the recording capacity of the magnetic tape 204 becomes smaller.

Further, as shown in the example shown in FIG. 23, the reading head 200 is usually provided with a servo element 208. A servo pattern formed on the magnetic layer of the magnetic tape 204 is read by a servo element 208 . Then, based on the servo signal obtained by reading the servo pattern by the servo element 208, a control device (not shown) determines at which position on the magnetic tape 204 the reading element 202 travels at regular time intervals, for example. The animal is identified. As a result, a PES (Position Error Signal) in the width direction of the magnetic tape 204 is detected by the control device.

In this way, when the running position of the reading element 202 is specified by the control device, the control device performs feedback control on the actuator for the reading head (not shown) based on the specified running position. Accordingly, tracking in the width direction of the magnetic tape 204 is realized.

However, even if tracking is performed, steep vibrations, high frequency components of jitter, etc. become factors that increase PES, leading to a decrease in the reproduction quality of data read from the track to be read.
In contrast, a plurality of reading elements are used to read data from a specific track area including the track to be read among the track areas included in the magnetic tape, and a waveform is generated for each reading result for each reading element. If data originating from the track to be read is extracted from the read result by performing equalization processing, the data can be read from the track to be read compared to the case where data is read from the track to be read by only a single reading element. Data playback quality can be improved. As a result, it is possible to increase the allowable amount of deviation (track offset amount) that can ensure good reproduction quality.
However, if the fluctuation in the relative position between the reading element and the track to be read (hereinafter referred to as "relative position fluctuation") is large, the waveform equalization processing that is performed on each of the reading results for each of the multiple reading elements will be difficult. , it may not necessarily be said that the waveform equalization processing is optimal for each reading result. For example, the waveform equalization processing performed by a two-dimensional FIR filter determined according to the reading results of the servo pattern may not necessarily be the optimal waveform equalization processing for each reading result. On the other hand, if the above-mentioned relative position fluctuation can be suppressed, it becomes possible to perform more suitable waveform equalization processing on each of the reading results read by the plurality of reading elements. As a result, it is possible to increase the allowable amount of deviation that can ensure good reproduction quality for the data originating from the read target track that has been subjected to the above waveform equalization processing and extracted. In this regard, in the magnetic tape according to one embodiment of the present invention, if the ΔN of the magnetic layer is 0.25 or more and 0.40 or less, this leads to stabilizing the contact state between the magnetic tape and the reading element. Conceivable. It is presumed that this contributes to suppressing the above-mentioned relative position fluctuation. This point will be discussed further later.
Further, the closer the servo pattern is formed to a designed shape (for example, an ideal shape, which will be described in detail later), the higher the accuracy of identifying the position where the reading element is traveling becomes. This also leads to increasing the allowable amount of deviation (track offset amount) that can ensure good reproduction quality. In this regard, the difference (L _99.9 −L _0.1 ) is an index regarding the shape of the servo pattern (timing-based servo pattern). Details will be described later.
As mentioned above, being able to increase the allowable amount of deviation to ensure good playback quality means that even if the track margin (recording track width - playback element width) is reduced, good playback quality (for example, high SNR, low error rate) can be achieved. etc.) may contribute to making playback possible. The ability to reduce the track margin can contribute to reducing the recording track width and increasing the number of recording tracks that can be arranged in the width direction of the magnetic tape, that is, to increasing the capacity.

Below, a magnetic tape, a magnetic tape cartridge, and a magnetic tape device according to one aspect of the present invention will be described in more detail. Below, magnetic tape devices and the like may be explained with reference to the drawings. However, the present invention is not limited to the embodiments shown in the drawings.

[Configuration of magnetic tape device and magnetic tape reading process]
As shown in FIG. 1 as an example, a magnetic tape device 10 includes a magnetic tape cartridge 12, a transport device 14, a reading head 16, and a control device 18.

The magnetic tape device 10 is a device that extracts a magnetic tape MT from a magnetic tape cartridge 12 and reads data from the extracted magnetic tape MT using a read head 16 using a linear scan method. Data reading can also be referred to as data reproduction.

The control device 18 controls the entire magnetic tape device 10 . In one aspect, the control performed by the control device 18 may be realized by an ASIC (Application Specific Integrated Circuit). Further, in one aspect, the control performed by the control device 18 may be realized by an FPGA (Field-Programmable Gate Array). Further, the control performed by the control device 18 may be realized by a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). Further, the above control may be realized by a combination of two or more of AISC, FPGA, and computer.

The conveyance device 14 is a device that selectively conveys the magnetic tape MT in the forward direction and the reverse direction, and includes a delivery motor 20, a take-up reel 22, a take-up motor 24, a plurality of guide rollers GR, and a control device 18. ing.

A cartridge reel CR is provided inside the magnetic tape cartridge 12. A magnetic tape MT is wound around the cartridge reel CR. The feed motor 20 rotates the cartridge reel CR within the magnetic tape cartridge 12 under the control of the control device 18 . The control device 18 controls the rotation direction, rotation speed, rotation torque, etc. of the cartridge reel CR by controlling the delivery motor 20.

When the magnetic tape MT is taken up by the take-up reel 22, the control device 18 rotates the sending motor 20 so as to run the magnetic tape MT in the forward direction. The rotational speed, rotational torque, etc. of the delivery motor 20 are adjusted according to the speed of the magnetic tape MT being wound by the take-up reel 22.

The take-up motor 24 rotates the take-up reel 22 under the control of the control device 18 . The control device 18 controls the rotation direction, rotation speed, rotation torque, etc. of the take-up reel 22 by controlling the take-up motor 24 .

When the magnetic tape MT is taken up by the take-up reel 22, the control device 18 rotates the take-up motor 24 so as to run the magnetic tape MT in the forward direction. The rotational speed, rotational torque, etc. of the take-up motor 24 are adjusted according to the speed of the magnetic tape MT being wound up by the take-up reel 22.

By adjusting the rotational speed, rotational torque, etc. of each of the delivery motor 20 and the take-up motor 24 in this manner, tension within a predetermined range is applied to the magnetic tape MT. Here, "within a predetermined range" refers to a tension range obtained through computer simulation and/or actual machine testing, for example, as a tension range in which data can be read from the magnetic tape MT by the read head 16.

When rewinding the magnetic tape MT onto the cartridge reel CR, the control device 18 rotates the feed motor 20 and the take-up motor 24 so as to run the magnetic tape MT in the opposite direction.

In one aspect, the tension of the magnetic tape MT is controlled by controlling the rotational speed, rotational torque, etc. of the delivery motor 20 and the take-up motor 24. Further, in one aspect, the tension of the magnetic tape MT may be controlled using a dancer roller or by drawing the magnetic tape MT into a vacuum chamber.

Each of the plurality of guide rollers GR is a roller that guides the magnetic tape MT. The travel path of the magnetic tape MT is determined by a plurality of guide rollers GR being separately arranged at positions straddling the reading head 16 between the magnetic tape cartridge 12 and the take-up reel 22.

The reading head 16 includes a reading section 26 and a holder 28. The reading section 26 is held by a holder 28 so as to be in contact with the running magnetic tape MT.

As shown in FIG. 2 as an example, the magnetic tape MT includes a track area 30 and a servo pattern 32. The servo pattern 32 is a pattern used to detect the position of the read head 16 with respect to the magnetic tape MT. The servo pattern 32 has a first diagonal line 32A at a first predetermined angle (for example, 95 degrees) and a second diagonal line 32B at a second predetermined angle (for example, 85 degrees) at both ends in the tape width direction. This is a pattern that is alternately arranged at a constant pitch (period) along the running direction. The "tape width direction" here refers to the width direction of the magnetic tape MT.

The track area 30 is an area in which data to be read is written, and is formed at the center of the magnetic tape MT in the tape width direction. The "central portion in the tape width direction" herein refers to, for example, a region between the servo pattern 32 at one end of the magnetic tape MT in the tape width direction and the servo pattern 32 at the other end. Hereinafter, for convenience of explanation, the "running direction of the magnetic tape MT" will be simply referred to as the "running direction."

The reading section 26 includes a servo element pair 36 and a plurality of reading element units 38. The holder 28 is formed in an elongated shape in the tape width direction, and the total length of the holder 28 in the longitudinal direction is longer than the width of the magnetic tape MT. The servo element pairs 36 are arranged at both ends of the holder 28 in the longitudinal direction, and the plurality of reading element units 38 are arranged at the center of the holder 28 in the longitudinal direction.

Servo element pair 36 includes servo elements 36A and 36B. The servo element 36A is arranged at a position facing the servo pattern 32 at one end of the magnetic tape MT in the tape width direction, and the servo element 36B is arranged at a position facing the servo pattern 32 at the other end of the magnetic tape MT in the tape width direction. are placed in opposing positions.

In the holder 28, a plurality of reading element units 38 are arranged along the tape width direction between the servo elements 36A and 36B. The track area 30 includes a plurality of tracks equally spaced in the tape width direction, and in the default state of the magnetic tape device 10, each of the plurality of reading element units 38 faces each track in the track area 30. It is located.

Therefore, by linearly moving the reading unit 26 and the magnetic tape MT relative to each other along the longitudinal direction of the magnetic tape MT, the data of each track in the track area 30 can be read according to the position of the plurality of reading element units 38. is read by each corresponding reading element unit 38 using a linear scan method. Further, in the linear scan method, the servo pattern 32 is read by the servo element pair 36 in synchronization with the reading operation of the reading element unit 38. That is, in one aspect of the linear scan method, reading on the magnetic tape MT is performed in parallel by a plurality of reading element units 38 and servo element pairs 36.

Here, the above-mentioned "each track in the track area 30" refers to a track included in "each of a plurality of specific track areas each including a track to be read among the track areas included in the magnetic tape."

The above-mentioned "default state of the magnetic tape device 10" refers to a state where the magnetic tape MT is not deformed and the positional relationship between the magnetic tape MT and the reading head 16 is correct. Here, the "correct positional relationship" refers to, for example, a positional relationship in which the center of the magnetic tape MT in the tape width direction and the center of the reading head 16 in the longitudinal direction coincide.

In one aspect, each of the plurality of reading element units 38 has the same configuration. For convenience of explanation, one of the plurality of reading element units 38 will be described below as an example. As shown in FIG. 3 as an example, the reading element unit 38 includes a pair of reading elements. In the example shown in FIG. 3, "a pair of reading elements" refers to the first reading element 40 and the second reading element 42. Each of the first reading element 40 and the second reading element 42 reads data from a specific track area 31 of the track area 30 that includes the read target track 30A.

In the example shown in FIG. 3, one specific track area 31 is shown for convenience of explanation. Actually, normally, a plurality of specific track areas 31 exist in the track area 30, and each specific track area 31 includes the read target track 30A. One reading element unit 38 is assigned to each of the plurality of specific track areas 31. Specifically, one reading element unit 38 is assigned to each reading target track 30A of the plurality of specific track areas 31.

The specific track area 31 refers to three adjacent tracks. The first track among the three adjacent tracks is the read target track 30A in the track area 30. The second track among the three adjacent tracks is the first noise mixing source track 30B, which is one of the adjacent tracks adjacent to the read target track 30A. The third track among the three adjacent tracks is a second noise mixing source track 30C, which is one of the adjacent tracks adjacent to the read target track 30A. The track to be read 30A is a track at a position facing the reading element unit 38 in the track area 30. In other words, the read target track 30A refers to a track from which data of the read element unit 38 is read.

The first noise contamination source track 30B is adjacent to the read target track 30A on one side in the tape width direction, and is a track that is a source of noise mixed into the data read from the read target track 30A. be. The second noise source track 30C is adjacent to the read target track 30A on the other side in the tape width direction, and is a track that is a source of noise mixed into the data read from the read target track 30A. be. Hereinafter, for convenience of explanation, the first noise mixing source track 30B and the second noise mixing source track 30C will be referred to as "adjacent tracks" without any reference numerals unless it is necessary to explain them separately.

In one aspect, within the track area 30, a plurality of specific track areas 31 are arranged at regular intervals in the tape width direction. For example, within the track area 30, 32 specific track areas 31 are arranged at regular intervals in the tape width direction, and one reading element unit 38 is assigned to each specific track area 31.

The first reading element 40 and the second reading element 42 are disposed close to each other in the running direction and at positions where they partially overlap in the running direction. In the default state of the magnetic tape device 10, the first reading element 40 is arranged at a position straddling the read target track 30A and the first noise source track 30B. In the default state of the magnetic tape device 10, the second reading element 42 is arranged at a position straddling the read target track 30A and the first noise source track 30B.

In the default state of the magnetic tape device 10, the area of the portion of the first reading element 40 facing the track 30A to be read in plan view is the area of the first noise contamination source of the first reading element 40. It is larger than the area of the portion facing the track 30B. On the other hand, in the default state of the magnetic tape device 10, the area of the portion of the second reading element 42 facing the first noise source track 30B in plan view is as follows. The area is larger than the area of the portion facing the read target track 30A.

The data read by the first reading element 40 is subjected to waveform equalization processing by a first equalizer 70 (see FIG. 7), which will be described later. The data read by the second reading element 42 is subjected to waveform equalization processing by a second equalizer 72 (see FIG. 7), which will be described later. The respective data obtained by performing waveform equalization processing by each of the first equalizer 70 and the second equalizer 72 are combined by being added by the adder 44.

In FIG. 3, a mode in which the reading element unit 38 has a first reading element 40 and a second reading element 42 is explained as an example. However, for example, even if only one reading element (hereinafter also referred to as a single reading element) of a pair of reading elements is used, a signal corresponding to the reproduced signal obtained from the reading element unit 38 can be obtained.

In this case, for example, as shown in FIG. 8, the playback signal obtained from a single reading element is used as the plane position on the track calculated from the servo signal obtained by the servo element pair 36 in synchronization with the playback signal. Assign to By repeating this while moving the single reading element in the tape width direction, a two-dimensional image (hereinafter simply referred to as "two-dimensional image") of the reproduced signal is obtained. Here, the two-dimensional image or a reproduced signal constituting a part of the two-dimensional image (for example, a reproduced signal corresponding to the positions of a plurality of tracks) is a signal equivalent to the reproduced signal obtained from the reading element unit 38. be.

FIG. 24 shows an example of a two-dimensional image of a reproduced signal obtained using a loop tester for a looped magnetic tape MT (hereinafter also referred to as "loop tape"). Here, the loop tester refers to, for example, a device that conveys a loop tape while repeatedly contacting a single reading element. In order to obtain a two-dimensional image like a loop tester, a reel tester or an actual tape drive may be used. The term "reel tester" used herein refers to, for example, a device that transports the magnetic tape MT in the form of a reel.

In this way, even if a magnetic tape head without a reading element unit in which multiple reading elements are mounted in close proximity is used, the effects of the technology described in this specification can be quantitatively evaluated. . Examples of indicators for quantitatively evaluating the effects of the technology described in this specification include SNR, error rate, and the like.

4 to 6 show the results obtained through experiments conducted by the present inventors. As an example, as shown in FIG. 4, a reading element pair 50 is arranged on the track area 49. The track area 49 includes a first track 49A, a second track 49B, and a third track 49C that are adjacent to each other in the tape width direction. The reading element pair 50 includes a first reading element 50A and a second reading element 50B. The first reading element 50A and the second reading element 50B are arranged close to each other in the tape width direction. Further, the first reading element 50A is arranged to face the second track 49B, which is the track to be read, and to fit within the second track 49B. Further, the second reading element 50B is disposed so as to face the first track 49A adjacent to one side of the second track 49B and to fit within the first track 49A.

FIG. 5 shows an example of the correlation between SNR and track offset for each of the single read element data and the first composite data under the first condition. Further, FIG. 6 shows an example of the correlation between the SNR and the track offset for each of the single reading element data and the second composite data under the second condition.

Here, single reading element data refers to data obtained by performing waveform equalization processing on data read by the first reading element 50A, similar to the first reading element 40 shown in FIG. Point. The first condition refers to a condition where the reading element pitch is 700 nm (nanometers). The second condition refers to a condition where the reading element pitch is 500 nm. The reading element pitch refers to the pitch between the first reading element 50A and the second reading element 50B in the tape width direction, as shown in FIG. 4 as an example. As shown in FIG. 4 as an example, the track offset refers to the amount of deviation between the center of the second track 49B in the tape width direction and the center of the first reading element 50A in the track width direction.

The first synthesized data refers to data that is synthesized by adding the first waveform equalized data and the second waveform equalized data obtained under the first condition. The first waveform equalized data refers to data obtained by performing waveform equalization processing on data read by the first reading element 50A, similar to the first reading element 40 shown in FIG. Point. The second waveform equalized data refers to data obtained by subjecting the data read by the second reading element 50B to waveform equalization processing, similar to the second reading element 42 shown in FIG. Point. The second composite data refers to data that is synthesized by adding the first waveform equalized data and the second waveform equalized data obtained under the second condition.

Comparing the SNR of the first composite data shown in FIG. 5 and the SNR of the second composite data shown in FIG. In contrast, the SNR of the second composite data does not drop suddenly in the middle like the graph of the SNR of the first composite data. Each of the SNR of the first composite data and the SNR of the second composite data is higher than the SNR of the single read element data, and in particular, the SNR of the second composite data is higher than the SNR of the single read element data over the entire range of track offsets. higher than the SNR of

Based on the experimental results shown in FIGS. 5 and 6, the present inventors found that the first reading element 50A and the second reading element 50B were It has been found that it is preferable to read data while the device is in close proximity to the device. The "close state" here means, for example, that the first reading element 50A and the second reading element 50B have an SNR higher than the SNR of single reading element data over the entire track offset range without contacting each other. Refers to the state in which the tapes are arranged side by side in the tape width direction so that the height is high.

In one embodiment, as shown in FIG. 3 as an example, in the reading element unit 38, the first reading element 40 and the second reading element 42 partially overlap each other in the running direction, so that the magnetic tape MT This has resulted in a higher density of tracks included in the system.

As shown in FIG. 7 as an example, the magnetic tape device 10 includes an actuator 60, an extraction section 62, A/D (Analog/Digital) converters 64, 66, 68, a decoding section 69, and a computer 73.

The control device 18 is connected to the servo element pair 36 via an A/D (Analog/Digital) converter 68. The A/D converter 68 converts an analog signal obtained by reading the servo pattern 32 by the servo elements 36A and 36B included in the servo element pair 36 into a digital signal, and sends the obtained servo signal to the control device 18. Output.

Control device 18 is connected to actuator 60 . The actuator 60 is attached to the reading head 16 and applies power to the reading head 16 under the control of the control device 18 to cause the reading head 16 to move in the tape width direction. The actuator 60 includes, for example, a voice coil motor, and the power applied to the reading head 16 is obtained by converting electrical energy based on a current flowing through the coil into kinetic energy using magnetic energy as a medium. It is the driving force.

Here, an example is given in which the actuator 60 is equipped with a voice coil motor. However, the above-described magnetic tape device is not limited to this embodiment, and for example, a piezoelectric element may be used instead of the voice coil motor. It is also possible to use a voice coil motor and a piezoelectric element together.

In one embodiment, the amount of positional deviation between the magnetic tape MT and the reading element unit 38 is determined according to a servo signal obtained by reading the servo pattern 32 by the servo element pair 36. The control device 18 controls the actuator 60 to apply power to the reading head 16 according to the amount of positional deviation between the magnetic tape MT and the reading element unit 38, thereby causing the reading head 16 to move in the tape width direction. and adjust the position of the reading head 16 to the normal position. Here, the normal position refers to the position of the read head 16 when the magnetic tape device 10 is in its default state, for example, as shown in FIG.

Here, a mode in which the amount of positional deviation between the magnetic tape MT and the reading element unit 38 is determined according to a servo signal obtained by reading the servo pattern 32 by the servo element pair 36 is illustrated. However, the magnetic tape device according to one embodiment of the present invention is not limited to such an example. For example, as the amount of positional deviation between the magnetic tape MT and the reading element unit 38, the amount of deviation between the servo element 36A and a predetermined reference position of the magnetic tape MT may be adopted, or the amount of deviation between the end surface of the reading head 16 and The amount of deviation from the center position of a specific track included in the magnetic tape MT may be used. The amount of positional deviation between the magnetic tape MT and the reading element unit 38 is thus the amount of deviation corresponding to the amount of deviation between the center of the track 30A to be read in the tape width direction and the center of the reading head 16 in the tape width direction. Good to have. Hereinafter, for convenience of explanation, the amount of positional deviation between the magnetic tape MT and the reading element unit 38 will be simply referred to as "the amount of deviation."

The amount of deviation is calculated based on the ratio of distance A to distance B, for example, as shown in FIG. The distance A refers to the distance calculated from the result obtained by reading the adjacent first diagonal line 32A and second diagonal line 32B by the servo element 36A. The distance B refers to the distance calculated from the result obtained by reading two adjacent first diagonal lines 32A by the servo element 36A.

The extraction unit 62 includes a control device 18 and a two-dimensional FIR filter 71. The two-dimensional FIR filter 71 includes an adder 44, a first equalizer 70, and a second equalizer 72.

The first equalizer 70 is connected to the first reading element 40 via an A/D converter 64. Further, the first equalizer 70 is connected to each of the control device 18 and the adder 44. The data read from the specific track area 31 by the first reading element 40 is an analog signal, and the A/D converter 64 converts the data read from the specific track area 31 by the first reading element 40 into a digital signal. The first read signal obtained by this is output to the first equalizer 70.

The second equalizer 72 is connected to the second read element 42 via the A/D converter 66. Further, the second equalizer 72 is connected to each of the control device 18 and the adder 44. The data read from the specific track area 31 by the second reading element 42 is an analog signal, and the A/D converter 66 converts the data read from the specific track area 31 by the second reading element 42 into a digital signal. The second read signal obtained by this is output to the second equalizer 72. Note that the first read signal and the second read signal are examples of "reading results for each reading element."

The first equalizer 70 performs waveform equalization processing on the input first read signal. For example, the first equalizer 70 convolutes the input first read signal with a tap coefficient, and outputs a first arithmetic-processed signal that is a signal after the arithmetic processing.

The second equalizer 72 performs waveform equalization processing on the input second read signal. For example, the second equalizer 72 convolutes the input second read signal with a tap coefficient, and outputs a second arithmetic-processed signal that is a signal after the arithmetic processing.

Each of the first equalizer 70 and the second equalizer 72 outputs the first arithmetic-processed signal and the second arithmetic-processed signal to the adder 44 . The adder 44 combines the first arithmetic-processed signal input from the first equalizer 70 and the second arithmetic-processed signal input from the second equalizer 72, The combined data obtained by combining is output to the decoding section 69.

Each of the first equalizer 70 and the second equalizer 72 is a one-dimensional FIR filter.

In one aspect, the FIR filter itself is a series of real values including positive and negative values, the number of rows in the series is referred to as the number of taps, and the numbers themselves are referred to as tap coefficients. Furthermore, in one aspect, waveform equalization refers to a process in which a read signal is subjected to a convolution operation (product summation) with the above-mentioned series of real values, that is, tap coefficients. The "read signal" here refers to the first read signal and the second read signal. In one aspect, the equalizer refers to a circuit that performs a process of convolving a read signal or other input signal with a tap coefficient and outputting a signal after the calculation process. Further, in one aspect, an adder refers to a circuit that simply adds two series. The weighting of the two series is reflected in the numerical values of the FIR filters used in the first equalizer 70 and the second equalizer 72, that is, the tap coefficients.

The control device 18 sets tap coefficients according to the amount of deviation for each of the FIR filters of the first equalizer 70 and the second equalizer 72, thereby controlling the FIR filters of the first equalizer 70 and the second equalizer 72. Each of the equalizers 72 is caused to perform waveform equalization processing according to the amount of deviation.

The control device 18 includes a correspondence table 18A. In the correspondence table 18A, tap coefficients and deviation amounts are associated with each other for the first equalizer 70 and the second equalizer 72. The combination of the tap coefficient and the amount of deviation is, for example, a combination of the tap coefficient and the amount of deviation that allows the best composite data to be obtained by the adder 44 based on the results of at least one of an actual machine test and a simulation. This is a combination obtained in advance as . The "best composite data" here refers to data corresponding to the track data to be read.

Here, "read target track data" refers to "data originating from the read target track 30A". In other words, "data originating from the read target track 30A" refers to data corresponding to data written in the read target track 30A. An example of data corresponding to the data written in the read target track 30A is data read from the read target track 30A and which is not mixed with noise components from adjacent tracks.

In the above, the correspondence table 18A is illustrated. In other embodiments, an arithmetic expression may be used instead of the correspondence table 18A. The term "arithmetic expression" used herein refers to, for example, an arithmetic expression in which the independent variable is the amount of deviation and the dependent variable is the tap coefficient.

In the above description, a mode is mentioned in which the tap coefficients are derived from the correspondence table 18A in which combinations of tap coefficients and deviation amounts are defined. In other embodiments, for example, the tap coefficients may be derived from a correspondence table or an arithmetic expression in which combinations of tap coefficients and ratios are defined. The "ratio" here refers to the ratio of the overlapping area with the reading target track 30A and the overlapping area with the adjacent track for each of the first reading element 40 and the second reading element 42. The ratio is specified by the control device 18 by being calculated from the amount of deviation, and a tap coefficient is determined according to the specified ratio. Alternatively, in one aspect, a series of a plurality of tap coefficients is created using, for example, a plurality of reading results obtained by each of a plurality of reading elements reading data in advance in a calibration area, and a base that is an equalization target is used. It can also be determined to minimize the error from the waveform (target).

The decoding unit 69 decodes the composite data input from the adder 44 and outputs the decoded signal to the computer 73. The computer 73 performs various processes on the decoded signal input from the decoder 69.

Next, the magnetic tape reading process executed by the extraction unit 62 will be described with reference to FIG. For convenience of explanation, the following description will be made on the premise that a servo signal is input to the control device 18 when the sampling time arrives. Here, sampling means not only sampling of servo signals but also sampling of read signals. That is, in one aspect, since the track area 30 is formed parallel to the servo pattern 32 along the running direction, the reading operation of the reading element unit 38 is performed in synchronization with the reading operation of the servo element pair 36.

In the process shown in FIG. 9, first, in step 100, the control device 18 determines whether the sampling time has arrived. In step 100, if the sampling time has arrived, the determination is affirmative and the magnetic tape reading process moves to step 102. In step 100, if the sampling time has not arrived, the determination is negative and the determination in step 100 is performed again.

In step 102, the first equalizer 70 obtains a first read signal, the second equalizer 72 obtains a second read signal, and then the magnetic tape reading process moves to step 104.

In step 104, the control device 18 acquires the servo signal and calculates the amount of deviation from the acquired servo signal, and then the magnetic tape reading process moves to step 106.

In step 106, the control device 18 stores the tap coefficients corresponding to the deviation amounts calculated in the process in step 104 for the first to third taps of each of the first equalizer 70 and the second equalizer 72 in the correspondence table. Derived from 18A. That is, by executing the process of step 106, the optimal combination of the one-dimensional FIR filter, which is an example of the first equalizer 70, and the one-dimensional filter, which is an example of the second equalizer 72, is determined. determined. The term "optimal combination" as used herein refers to, for example, a combination in which the composite data outputted by executing the process of step 112, which will be described later, corresponds to the track data to be read.

In the next step 108, the control device 18 sets the tap coefficients derived in the process of step 106 for each of the first equalizer 70 and the second equalizer 72, and then the magnetic tape reading process continues in step 106. The process moves to 110.

In step 110, the first equalizer 70 generates a first arithmetic-processed signal by performing waveform equalization processing on the first read signal obtained in the processing in step 102. The first equalizer 70 outputs the generated first arithmetic processed signal to the adder 44 . The second equalizer 72 generates a second arithmetic-processed signal by performing waveform equalization processing on the second read signal obtained in the process of step 102. The second equalizer 72 outputs the generated second arithmetic processed signal to the adder 44 .

In the next step 112, the adder 44, as shown in FIG. The signal is synthesized by adding the two processed signals. Then, the adder 44 outputs the combined data obtained by combining to the decoding section 69.

When the reading element unit 38 is arranged on the specific track area 31 as in the example shown in FIG. Data corresponding to the track data to be read from which noise components have been removed is output. That is, by executing the processes from step 102 to step 112, the extraction unit 62 extracts only the data originating from the read target track 30A.

When the magnetic tape MT expands or contracts in the tape width direction or vibration is applied to at least one of the magnetic tape MT and the reading head 16, the reading element unit 38 moves from the position shown in FIG. 3 as an example to the position shown in FIG. It may be displaced to the position shown in . In the example shown in FIG. 11, the first reading element 40 and the second reading element 42 are arranged at positions that straddle both the reading target track 30A and the second noise source track 30C. In this case, by executing the processes from step 102 to step 112, data corresponding to the read target track data from which the noise component from the second noise source track 30C has been removed is output to the decoding unit 69 as composite data. be done.

In the next step 114, the control device 18 determines whether conditions for terminating the magnetic tape reading process (hereinafter referred to as "termination conditions") are satisfied. The termination condition refers to, for example, a condition that the entire magnetic tape MT has been wound up by the take-up reel 22, a condition that an instruction to forcibly terminate the magnetic tape reading process has been given from the outside, and the like.

In step 114, if the termination condition is not satisfied, the determination is negative and the magnetic tape reading process proceeds to step 100. In step 114, if the termination condition is satisfied, the determination is affirmative and the magnetic tape reading process is terminated.

As described above, in one embodiment of the magnetic tape device 10, data is read from the specific track area 31 by the first reading element 40 and the second reading element 42, which are arranged in close proximity to each other. Then, the extraction unit 62 performs waveform equalization processing on each of the first reading element 40 and the second reading element 42 according to the amount of deviation, thereby converting the first read signal and the second read signal into , data originating from the read target track 30A is extracted. Therefore, the magnetic tape device 10 reduces the deterioration in the playback quality of data read from the read track 30A using the linear scan method, compared to the case where data is read from the read track 30A using a linear scan method using only a single reading element. Can be suppressed.

Further, in one embodiment of the magnetic tape device 10, the first reading element 40 and the second reading element 42 partially overlap each other in the running direction. Therefore, the magnetic tape device 10 can improve the reproduction quality of data read from the read target track 30A using the linear scan method, compared to a case where the plurality of reading elements entirely overlap each other in the running direction.

Further, in one aspect of the magnetic tape device 10, the specific track area 31 includes a read target track 30A, a first noise source track 30B, and a second noise source track 30C, and includes a first reading element 40 and a second noise source track 30C. Each of the two reading elements 42 straddles both the read target track 30A and the adjacent track when the positional relationship with the magnetic tape MT changes. Therefore, compared to the case where data is read from the read target track 30A by only a single read element, in the magnetic tape device 10, the data enters the adjacent track from the read target track 30A in the tape width direction. The noise component generated in one of the two reading elements 42 can be reduced by using the reading result of the other reading element that enters an adjacent track from the target track 30A to be read in the tape width direction.

Further, in one aspect of the magnetic tape device 10, the tap coefficient used in the waveform equalization process is determined according to the amount of deviation. By determining the tap coefficient according to the amount of deviation, compared to the case where the tap coefficient is determined according to a parameter unrelated to the amount of deviation, noise caused by entering the target track 30A from adjacent tracks in the tape width direction is reduced. The component can be immediately reduced by following changes in the positional relationship between the magnetic tape MT and the reading element unit 38.

Further, in one aspect of the magnetic tape device 10, for each of the first reading element 40 and the second reading element 42, the ratio of the overlapping area with the read target track 30A and the overlapping area with the adjacent track is specified from the amount of deviation. , a tap coefficient is determined according to the specified ratio. Thereby, the magnetic tape device 10 determines the tap coefficient according to a parameter that is unrelated to the ratio of the overlapping area with the read target track 30A and the overlapping area with the adjacent track for each of the plurality of reading elements. Compared to the case, even if the positional relationship between the magnetic tape MT and the reading element unit 38 changes, the noise component can be reduced more accurately.

Further, in one aspect of the magnetic tape device 10, the amount of deviation is determined according to the result obtained by reading the servo pattern 32 by the servo element pair 36. Thereby, the magnetic tape device 10 can determine the amount of deviation more easily than in the case where the servo pattern 32 is not provided on the magnetic tape MT.

Further, in one aspect of the magnetic tape device 10, the reading operation of the reading element unit 38 is performed in synchronization with the reading operation of the servo element pair 36. As a result, compared to magnetic disks and helical scan magnetic tapes in which servo patterns and data cannot be read in synchronization, the magnetic tape device 10 is able to easily enter the track to be read from adjacent tracks in the width direction of the magnetic tape. The generated noise components can be instantly reduced.

Further, in one embodiment of the magnetic tape device 10, the extraction unit 62 includes a two-dimensional FIR filter 71. Then, the two-dimensional FIR filter 71 performs waveform equalization processing on each of the first read signal and the second read signal, and synthesizes the results obtained. Data originating from the read target track 30A is extracted from the 2 read signal. Thereby, the magnetic tape device 10 can quickly extract data originating from the read target track 30A from the first read signal and the second read signal, compared to the case where only a one-dimensional FIR filter is used. Furthermore, the magnetic tape device 10 can perform calculations with a smaller amount of calculations than when performing matrix calculations.

Further, in one embodiment of the magnetic tape device 10, a first reading element 40 and a second reading element 42 are employed as a pair of reading elements. Thereby, the magnetic tape device 10 can contribute to miniaturization of the reading element unit 38 compared to the case where three or more reading elements are used. By downsizing the reading element unit 38, the reading section 26 and the reading head 16 can also be downsized. Furthermore, the magnetic tape device 10 can also suppress the occurrence of a situation in which adjacent reading element units 38 come into contact with each other.

Further, in one embodiment of the magnetic tape device 10, each of the plurality of reading element units 38 reads data from the corresponding read target track 30A included in each of the plurality of specific track areas 31 using a linear scan method. As a result, the magnetic tape device 10 can quickly complete the reading of data from the plurality of tracks 30A to be read, compared to the case where data is read from each of the plurality of tracks 30A to be read by only the single reading element unit 38. can do.

In the above embodiment, in the default state of the magnetic tape device 10, each of the first reading element 40 and the second reading element 42 reads both the target track 30A and the first noise source track 30B. However, the magnetic tape device described above is not limited to this embodiment. In the example shown in FIG. 12, a reading element unit 138 is employed in place of the reading element unit 38 described above. The reading element unit 138 includes a first reading element 140 and a second reading element 142. In the default state of the magnetic tape device 10, the center of the first reading element 140 in the tape width direction coincides with the center CL of the read target track 30A in the tape width direction. In addition, in the default state of the magnetic tape device 10, the first reading element 140 and the second reading element 142 read data without protruding into the first noise mixing source track 30B and the second noise mixing source track 30C. It is within the target track 30A. Furthermore, in the default state of the magnetic tape device 10, each of the first reading element 140 and the second reading element 142 is set in the running direction, similar to the first reading element 40 and the second reading element 42 described in the above embodiment. They are placed so that they partially overlap each other.

As an example, as shown in FIG. 12, even if the first reading element 140 and the second reading element 142 face the reading target track 30A without protruding from the reading target track 30A, the reading element unit 138 The positional relationship with the magnetic tape MT may change. That is, there are cases in which the reading element unit 138 straddles the reading target track 30A and the first noise mixing source track 30B, and cases in which the reading element unit 138 straddles the reading target track 30A and the second noise mixing source track 30C. . Even in these cases, by executing the processes of steps 102 to 112 described above, reading from which noise components from the first noise contamination source track 30B or the second noise contamination source track 30C is removed is performed. It becomes possible to obtain data corresponding to target track data.

In addition, since the first reading element 140 and the second reading element 142 are arranged at a position where they partially overlap each other in the running direction, from the part of the target track 30A to be read that cannot be read by the first reading element 140. The second reading element 142 can read data. As a result, the reliability of the track data to be read can be improved compared to the case where the first reading element 140 alone reads data from the track to be read 30A.

As an example, as shown in FIG. 11, in the default state of the magnetic tape device 10, each of the first reading element 40 and the second reading element 42 reads the target track 30A and the second noise source track 30C. It may be arranged in a position that straddles both.

Furthermore, in the above description, the reading element unit 38 including the first reading element 40 and the second reading element 42 has been illustrated. However, the above magnetic tape device is not limited to this embodiment. In the example shown in FIG. 13, a reading element unit 238 is used instead of the reading element unit 38. The reading element unit 238 differs from the reading element unit 38 in that it includes a third reading element 244. In the default state of the magnetic tape device 10, the third reading element 244 and the first reading element 40 are arranged at a position where they partially overlap with each other in the running direction. Further, in the default state of the magnetic tape device 10, the third reading element 244 is arranged at a position spanning the read target track 30A and the second noise source track 30C.

In this case, similarly to the case where the first equalizer 70 is assigned to the first read element 40 and the second equalizer 72 is assigned to the second read element 42, the third equalizer 70 is assigned to the third read element 244. 3 equalizers (not shown) are assigned. The third equalizer also has the same function as the first equalizer and the second equalizer described above, and is applied to the third read signal read by the third read element 244. Perform waveform equalization processing. Then, the third equalizer performs a convolution operation, for example, with a tap coefficient on the third read signal, and outputs a third arithmetic-processed signal that is a signal after the arithmetic processing. The adder 44 outputs a first arithmetic processed signal corresponding to the first read signal, a second arithmetic processed signal corresponding to the second read signal, and a third arithmetic processed signal corresponding to the third read signal. The signals are combined by adding the signals, and the resulting combined data is output to the decoding unit 69.

In the example shown in FIG. 13, in the default state of the magnetic tape device 10, the third reading element 244 is disposed at a position straddling the read target track 30A and the second noise mixing source track 30C. The technology is not limited to this. In the default state of the magnetic tape device 10, the third reading element 244 may be arranged at a position facing the target track 30A without protruding from the target track 30A.

Furthermore, in the above description, the reading element unit 38 is illustrated. However, the above magnetic tape device is not limited to this embodiment. For example, instead of the reading element unit 38, a reading element pair 50 shown in FIG. 4 may be employed. In this case, the first reading element 50A and the second reading element 50B are arranged close to each other in the tape width direction. In addition, the first reading element 50A and the second reading element 50B do not come into contact with each other, and as shown in FIG. The tapes should be arranged side by side in the tape width direction.

In the example shown in FIG. 4, for example, the first reading element 50A is located within the second track 49B in plan view, and the second reading element 50B is located within the first track 49A in plan view.

Furthermore, in the above description, the servo element pair 36 is illustrated. However, the above magnetic tape device is not limited to this embodiment. For example, instead of the servo element pair 36, one of the servo elements 36A and 36B may be employed.

Further, in the above description, a mode has been described in which a plurality of specific track areas 31 are arranged at regular intervals in the tape width direction within the track area 30. However, the above magnetic tape device is not limited to this embodiment. For example, among the plurality of specific track areas 31, in two adjacent specific track areas 31, one specific track area 31 and the other specific track area 31 overlap by one track in the tape width direction. They may be arranged in the direction. In this case, one adjacent track (for example, the first noise source track 30B) included in one specific track area 31 becomes the read target track 30A in the other specific track area 31. Further, the read target track 30A included in one specific track area 31 becomes an adjacent track area (for example, the second noise source track 30C) in the other specific track area 31.

The configuration of the magnetic tape device and the magnetic tape reading process described above are merely examples. Therefore, it goes without saying that unnecessary steps can be deleted, new steps can be added, and the processing order can be changed without departing from the main idea.
Further, the magnetic tape device can read (reproduce) data recorded on a magnetic tape, and can also have a configuration for recording data on a magnetic tape.

[Magnetic tape]
Next, details of the magnetic tape according to one embodiment of the present invention will be described.

A magnetic tape according to one embodiment of the present invention includes a nonmagnetic support and a magnetic layer containing ferromagnetic powder and a binder. The magnetic layer has a timing-based servo pattern, and the edge shape of the timing-based servo pattern identified by magnetic force microscopy is a cumulative distribution function of 99. The magnetic layer has a shape in which the difference (L _99.9 - L _0.1 ) between the 9% value L _99.9 and the 0.1% value L _0.1 of the cumulative distribution function is 180 nm or less, and the magnetic layer The absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction and the refractive index Nz measured in the thickness direction of the magnetic layer is 0.25 or more and 0.40 or less.

In recent years, timing-based servo systems have been widely used as systems using head tracking servos that utilize servo signals (hereinafter referred to as "servo systems"). In a timing-based servo type servo system (hereinafter referred to as a "timing-based servo system"), a plurality of servo patterns of two or more different shapes are formed on a magnetic layer, and a servo element has two or more different shapes of servo patterns. The position of the servo element is recognized based on the time interval at which the servo pattern was reproduced (read) and the time interval at which two servo patterns having the same shape were reproduced.
The term "timing-based servo pattern" used in the present invention and this specification refers to a servo pattern that allows head tracking in a timing-based servo system. A servo pattern that allows head tracking in a timing-based servo system is formed as multiple servo patterns of two or more different shapes on a magnetic layer by a servo write head, which is a head for forming servo patterns. be done. In one example, a plurality of servo patterns of two or more different shapes are consecutively arranged at a constant interval between servo patterns of the same kind of shape. In another example, different types of servo patterns are alternately arranged. Note that as long as the servo patterns have the same type of shape, there is no problem with positional displacement of the edge shapes of the servo patterns. The shape and arrangement of servo patterns on servo bands that enable head tracking in timing-based servo systems are well known, and specific aspects will be described later. Hereinafter, the timing-based servo pattern will also be simply referred to as a servo pattern. In the present invention and this specification, the edge shape specified by magnetic force microscopy observation of a timing-based servo pattern is the running direction of the magnetic tape when recording data (information) (hereinafter also simply referred to as the "running direction"). ) is the shape of the edge located on the downstream side.

Next, in the present invention and this specification, the edge shape specified by magnetic force microscopy observation of the timing-based servo pattern, and the cumulative distribution function 99 of the positional deviation width of this edge shape from the ideal shape in the longitudinal direction of the magnetic tape. The difference (L _99.9 −L _0.1 ) between the value L _99.9 of 9% and the value L _0.1 of the cumulative distribution function 0.1% and the ideal shape will be explained.
In the following description, a linear servo pattern that extends continuously from one side to the other in the width direction of the magnetic tape and is inclined at an angle α with respect to the width direction of the magnetic tape will be mainly described as an example. The angle α above refers to the line segment connecting the two ends in the tape width direction of the edge of the servo pattern located on the downstream side with respect to the running direction of the magnetic tape when recording data (information), and the magnetic tape. It refers to the angle formed with the width direction. This point will be further explained below.

For example, in magnetic tapes that are applied to the linear scan method, which is widely used as a recording method for magnetic tape devices, a region in which a servo pattern is formed (called a "servo band") is usually formed on the magnetic layer. There are multiple along the longitudinal direction. The area between the two servo bands is called a data band. Information (magnetic signals) is recorded on data bands, and each data band has a plurality of data tracks formed along its length. FIG. 14 shows an example of the arrangement of data bands and servo bands. In FIG. 14, a plurality of servo bands 1 are arranged between guide bands 3 on the magnetic layer of the magnetic tape MT. A plurality of areas 2 sandwiched between two servo bands are data bands. A servo pattern is a magnetized region, and is formed by magnetizing a specific region of a magnetic layer with a servo write head. The area that is magnetized by the servo write head (the position where the servo pattern is formed) is determined by standards. For example, in the industry standard LTO Ultrium format tape, a plurality of servo patterns are formed on a servo band at an angle with respect to the tape width direction, as shown in FIG. 15, when the magnetic tape is manufactured. Specifically, in FIG. 15, servo frame SF on servo band 1 is composed of servo subframe 1 (SSF1) and servo subframe 2 (SSF2). The servo subframe 1 is composed of an A burst (symbol A in FIG. 15) and a B burst (symbol B in FIG. 15). The A burst consists of servo patterns A1 to A5, and the B burst consists of servo patterns B1 to B5. On the other hand, the servo subframe 2 is composed of a C burst (symbol C in FIG. 15) and a D burst (symbol D in FIG. 15). The C burst consists of servo patterns C1 to C4, and the D burst consists of servo patterns D1 to D4. These 18 servo patterns are arranged in sets of 5 and 4 in subframes arranged in a 5, 5, 4, 4 arrangement, and are used to identify servo frames. Although one servo frame is shown in FIG. 15, a plurality of servo frames are arranged in each servo band in the traveling direction. In FIG. 15, the arrow indicates the running direction. The direction of travel of the arrow is the upstream side, and the opposite side is the downstream side.

16 and 17 are explanatory diagrams of the angle α. In the servo patterns shown in FIG. 15, for servo patterns that are inclined toward the upstream side in the running direction, such as servo patterns A1 to A5 and C1 to C4, connect the two ends of the downstream edge E _L. The angle between the line segment (broken line L1 in FIG. 16) and the tape width direction (broken line L2 in FIG. 16) is defined as angle α. On the other hand, for servo patterns that are inclined toward the downstream side in the running direction, such as servo patterns B1 to B5 and D1 to D4, a line connecting two ends of the downstream edge E _L (in FIG. , broken line L1) and the tape width direction (broken line L2 in FIG. 17) is defined as angle α. This angle α is generally called the azimuth angle, and is determined by the setting of the servo write head when forming the magnetized region (servo pattern) on the servo band.

When forming a magnetized region (servo pattern) on a servo band, if the servo pattern is ideally formed, the edge shape of the servo pattern inclined at an angle α with respect to the width direction of the magnetic tape will be as described above. This matches the shape of the line segment (broken line L1 in FIGS. 16 and 17) connecting the two edge ends. In other words, it becomes a straight line. Therefore, at each location on the edge, the width of positional deviation from the ideal shape in the longitudinal direction of the magnetic tape (hereinafter also simply referred to as "positional deviation width") is zero. On the other hand, as an example shown in FIG. 18, the edge shape of the servo pattern may deviate from the ideal shape. The above difference (L _99.9 - L _0.1 ) is due to the fact that the positional deviation width from the ideal shape is small at each edge position of the servo pattern, and the variation in the value of positional deviation width at each edge position is small. This is a value that can be used as an indicator. The difference (L _99.9 −L _0.1 ) is a value determined by the following method.
The surface of the magnetic layer of the magnetic tape on which the servo pattern is formed is observed using a magnetic force microscope (MFM). The measurement range is a range that includes five servo patterns. For example, in the LTO Ultrium format tape, five servo patterns of A burst or B burst can be observed by setting the measurement range to 90 μm×90 μm. A servo pattern (magnetized region) is extracted by measuring the measurement range at a pitch of 100 nm (rough measurement). In the present invention and this specification, the term "magnetic layer surface" is used synonymously with the magnetic layer side surface of the magnetic tape.
Thereafter, in order to detect the boundary between the magnetized region and the non-magnetized region at the edge of the servo pattern located on the downstream side with respect to the running direction, measurements are performed at a pitch of 5 nm near the boundary to obtain a magnetic profile. If the obtained magnetic profile is inclined at an angle α with respect to the width direction of the magnetic tape, the analysis software corrects the rotation along the width direction of the magnetic tape (so that α=0°). Thereafter, the position coordinates of the peak values of each profile measured at a pitch of 5 nm are calculated using analysis software. The position coordinates of this peak value indicate the position of the boundary between the magnetized region and the non-magnetized region. The position coordinates are specified by, for example, an xy coordinate system in which the traveling direction is the x coordinate and the width direction is the y coordinate.
Taking as an example the case where the ideal shape is a straight line and the position coordinates of a certain position on the straight line are (x, y) = (a, b), the actually obtained edge shape (position coordinates of the above boundary) If it matches the ideal shape, the calculated position coordinates will be (x, y) = (a, b). In this case, the displacement width is zero. On the other hand, if the actually obtained edge shape deviates from the ideal shape, the x coordinate of the position y=b of the boundary becomes x=a+c or x=ac. x = a + c, for example, is a case where there is a width c shift upstream with respect to the running direction, and x = a - c, for example, is a case where there is a width c shift downstream with respect to the running direction (i.e., with respect to the upstream side) Then -c) there is a deviation. Here, c is the positional deviation width. That is, the absolute value of the positional deviation width of the x-coordinate from the ideal shape is the positional deviation width from the ideal shape in the longitudinal direction of the magnetic tape. In this way, the positional deviation width at each location on the downstream edge in the running direction is determined by measurement at a pitch of 5 nm.
A cumulative distribution function is obtained using analysis software from the values obtained for each servo pattern. From the obtained cumulative distribution function, the value L _99.9 of 99.9% of the cumulative distribution function and the value L _0.1 of 0.1% are determined, and the difference (L _{99.9) is calculated for each servo pattern from the determined values. 9} -L _0.1 ).
The above measurements are performed in three different measurement ranges (number of measurements N=3).
The arithmetic mean of the differences (L _99.9 -L _0.1 ) obtained for each servo pattern is defined as the above difference (L _99.9 -L _0.1 ) for the magnetic tape.

The "ideal shape" of the edge shape of a servo pattern in the present invention and this specification refers to the edge shape when the servo pattern is formed without positional deviation. For example, in one embodiment, the servo pattern is a linear servo pattern that extends continuously or discontinuously from one side to the other in the width direction of the magnetic tape. Note that "straight line" with respect to the servo pattern means that the pattern shape does not include a curved portion, regardless of the positional deviation of the edge shape. "Continuous" means extending from one side of the tape width direction to the other side without any inflection point of the inclination angle and without interruption. An example of a servo pattern that extends continuously from one side to the other in the width direction of the magnetic tape is the servo pattern shown in FIG. On the other hand, "discontinuous" means that there is one or more inflection points of the inclination angle and/or that the inclination angle is interrupted and extends at one or more places. A shape that has an inflection point in the inclination angle but extends without interruption is a so-called polygonal shape. An example of a discontinuous servo pattern in which the inflection point of the inclination angle is one and extends continuously from one side to the other in the tape width direction is the servo pattern shown in FIG. On the other hand, an example of a discontinuous servo pattern in which the inclination angle is interrupted at one point without an inflection point and extends from one side to the other in the tape width direction is the servo pattern shown in FIG. Further, an example of a discontinuous servo pattern in which the inclination angle has one inflection point, is interrupted at one point, and extends from one side to the other in the tape width direction is the servo pattern shown in FIG.
Regarding a linear servo pattern that extends continuously from one side to the other in the tape width direction, the "ideal shape" of the edge shape is defined as connecting the two ends of the downstream edge of the linear servo pattern in the running direction. It is the shape of a line segment (linear shape). For example, the linear servo pattern shown in FIG. 15 has a straight line shape indicated by L1 in FIG. 16 or 17. On the other hand, for linear servo patterns that extend discontinuously, the ideal shape is the shape of a line segment connecting one end of a part with the same inclination angle to the other end (linear shape) for a shape with an inflection point of the inclination angle. It is. In addition, a shape that is interrupted at one or more places is a shape of a line segment (straight line shape) that connects one end to the other end of each part that extends continuously. For example, in the servo pattern shown in FIG. 19, there is a line segment connecting e1 and e2, and a line segment connecting e2 and e3. The servo pattern shown in FIG. 20 is a line segment connecting e4 and e5, and a line segment connecting e6 and e7. The servo pattern shown in FIG. 21 is a line segment connecting e8 and e9, and a line segment connecting e10 and e11.

In the above description, a linear servo pattern has been described as an example. However, the servo pattern may have an ideal edge shape having a curved shape. For example, for a servo pattern whose edge shape on the downstream side with respect to the running direction is ideally a partial arc shape, a magnetic force microscope of the edge shape on the downstream side with respect to the running direction is used with respect to the position coordinates of this partial arc. The difference (L _99.9 −L _0.1 ) can be determined from the positional deviation width determined from the determined position coordinates.

As the magnetic force microscope used in the above measurements, a commercially available or known magnetic force microscope is used in frequency modulation (FM) mode. As a probe for a magnetic force microscope, for example, SSS-MFMR manufactured by Nanoworld (nominal radius of curvature 15 nm) can be used. The distance between the magnetic layer surface and the tip of the probe during magnetic force microscopy is in the range of 20 to 50 nm.
Moreover, as the analysis software, commercially available analysis software or analysis software incorporating a known arithmetic expression can be used.

Next, in the present invention and this specification, the absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is determined by the following method. Let it be the required value. In the present invention and this specification, "the surface of the magnetic layer" has the same meaning as the surface of the magnetic tape on the magnetic layer side.

The refractive index in each direction of the magnetic layer is determined by spectroscopic ellipsometry using a two-layer model. In order to determine the refractive index of a magnetic layer using a two-layer model using spectroscopic ellipsometry, the value of the refractive index of a portion adjacent to the magnetic layer is used. In the following, an example will be explained in which the refractive indices Nxy and Nz of the magnetic layers are determined for a magnetic tape having a layered structure in which a nonmagnetic layer and a magnetic layer are laminated in this order on a nonmagnetic support. However, the magnetic tape according to one embodiment of the present invention can also be a magnetic tape having a layered structure in which a magnetic layer is directly laminated on a nonmagnetic support without intervening a nonmagnetic layer. For a magnetic tape having such a configuration, the refractive index in each direction of the magnetic layer is determined using a two-layer model of a magnetic layer and a nonmagnetic support in the same manner as described below. Furthermore, the angle of incidence described below is the angle of incidence when the angle of incidence in the case of vertical incidence is 0°.
(1) Preparation of measurement sample For magnetic tapes that have a backcoat layer on the surface opposite to the surface with the magnetic layer of the nonmagnetic support, remove the backcoat layer of the measurement sample cut from the magnetic tape. Then take measurements. The back coat layer can be removed by a known method such as dissolving the back coat layer using a solvent. As the solvent, for example, methyl ethyl ketone can be used. However, any solvent that can remove the back coat layer may be used. The surface of the nonmagnetic support after the backcoat layer has been removed is roughened by a known method so that reflected light from this surface is not detected during measurement with an ellipsometer. The surface roughening can be performed by a known method such as polishing the surface of the nonmagnetic support after the backcoat layer has been removed using sandpaper. For a measurement sample cut from a magnetic tape without a back coat layer, the surface of the nonmagnetic support opposite to the surface having the magnetic layer is roughened.
Furthermore, in order to measure the refractive index of the nonmagnetic layer described below, the magnetic layer is further removed to expose the surface of the nonmagnetic layer. In order to measure the refractive index of the nonmagnetic support described below, the nonmagnetic layer is also removed to expose the surface of the nonmagnetic support on the magnetic layer side. Removal of each layer can be performed by a known method as described for the removal of the back coat layer. Note that the longitudinal direction described below refers to the direction that was the longitudinal direction of the magnetic tape when the measurement sample was included in the magnetic tape before being cut out. This point also applies to other directions described below.
(2) Measurement of the refractive index of the magnetic layer Using an ellipsometer, the angle of incidence was set to 65°, 70°, and 75°, and incident light with a beam diameter of 300 μm was irradiated onto the surface of the magnetic layer from the longitudinal direction. The phase difference between polarized light and p-polarized light) and Ψ (amplitude ratio between s-polarized light and p-polarized light) are measured. The measurement is performed by changing the wavelength of the incident light in the range of 400 to 700 nm in steps of 1.5 nm, and a measured value is obtained for each wavelength.
Using the measured values of Δ and Ψ of the magnetic layer at each wavelength, the refractive index of the non-magnetic layer in each direction determined by the method below, and the thickness of the magnetic layer, the magnetic layer at each wavelength is calculated using the two-layer model as follows. Find the refractive index of
The zeroth layer of the two-layer model substrate is a nonmagnetic layer, and the first layer is a magnetic layer. A two-layer model is created by considering only the reflection at the interface between the air/magnetic layer and the magnetic layer/non-magnetic layer, and assuming that there is no influence from the back surface reflection of the non-magnetic layer. The refractive index of the first layer that best matches the obtained measured value is determined by fitting using the least squares method. As values at a wavelength of 600 nm obtained from the fitting results, the refractive index Nx of the magnetic layer in the longitudinal direction and the refractive index Nz ₁ in the thickness direction of the magnetic layer measured with incident light incident from the longitudinal direction are determined.
Similar to the above except that the direction in which the incident light is incident is the width direction of the magnetic tape, the refractive index Ny of the magnetic layer in the width direction and the incident light from the width direction are the values at a wavelength of 600 nm obtained from the fitting results. The refractive index Nz ₂ in the thickness direction of the magnetic layer measured by incident light is determined.
Fitting is performed using the following method.
Generally, "complex refractive index n=η+iκ". Here, η is the real part of the refractive index, κ is the extinction coefficient, and i is an imaginary number. The complex permittivity ε=ε1+iε2 (ε1 and ε2 satisfy the Kramers-Kronig relationship) has the relationship ε1=η ² −κ ² , ε2=2ηκ, and when calculating Nx and Nz ₁ , the complex of Nx Let the dielectric constant be ε _x =ε _x 1+iε _x 2, and let the complex permittivity of Nz ₁ be ε _z1 =ε _z1 1+iε _z1 2.
Let ε _x 2 be one Gaussian, start from any point where the peak position is 5.8 to 5.1 eV and σ is 4 to 3.5 eV, and set the dielectric constant outside the measurement wavelength range (400 to 700 nm). A parameter serving as an offset is placed in , and Nx is determined by performing least squares fitting on the measured values. Similarly, ε _z1 2 can be calculated by using an arbitrary point where the peak position is 3.2 to 2.9 eV and σ is 1.5 to 1.2 eV as the starting point, setting an offset parameter, and performing least squares fitting on the measured values. Find Nz ₁ . Ny and Nz ₂ are determined in the same manner. The refractive index Nxy measured in the in-plane direction of the magnetic layer is determined as "Nxy=(Nx+Ny)/2". The refractive index Nz measured in the thickness direction of the magnetic layer is determined as "Nz=(Nz ₁ +Nz ₂ )/2". From the obtained Nxy and Nz, the absolute value ΔN of the difference between these is obtained.
(3) Measurement of refractive index of non-magnetic layer The refractive index of the non-magnetic layer at a wavelength of 600 nm (refractive index in the longitudinal direction, refractive index in the width direction, incident light is incident from the longitudinal direction) is the same as the above method except for the following points. and the refractive index in the thickness direction measured by making incident light enter from the width direction.
The wavelength of the incident light is changed in steps of 1.5 nm in the range of 250 to 700 nm.
Using a two-layer model of a non-magnetic layer and a non-magnetic support, the 0th layer, which is the substrate of the two-layer model, is the non-magnetic support, and the first layer is the non-magnetic layer. A two-layer model is created by considering only the reflection at the interfaces of air/nonmagnetic layer and nonmagnetic layer/nonmagnetic support, and assuming that there is no influence of reflection from the back surface of the nonmagnetic support.
In fitting, seven peaks (0.6eV, 2.3eV, 2.9eV, 3.6eV, 4.6eV, 5.0eV, 6.0eV) are assumed for the imaginary part (ε2) of the complex permittivity. Then, a parameter that offsets the dielectric constant is placed outside the measurement wavelength range (250 to 700 nm).
(4) Measurement of refractive index of non-magnetic support The refractive index at a wavelength of 600 nm (refractive index in the longitudinal direction, refractive index in the width direction, The refractive index in the thickness direction measured by incident light from the longitudinal direction and the refractive index in the thickness direction measured by incident light from the width direction) are the refractive index of the magnetic layer, except for the following points. Determined in the same manner as above for measurement.
Instead of using a two-layer model, a one-layer model with only surface reflection is used.
Fitting is performed using the Cauchy model (n=A+B/λ ² , n is the refractive index, A and B are constants determined by the fitting, and λ is the wavelength).

When reading data recorded on a magnetic tape, the surface of the magnetic layer comes into contact with a reading element and the surface of the magnetic layer is scraped, which is thought to generate scraped debris (sometimes referred to as debris). The more scraps are present between the surface of the magnetic layer and the reading element, the more unstable the contact state between the surface of the magnetic layer and the reading element becomes. The inventors of the present invention conjecture that this causes a large variation in the relative position (relative position variation) between the reading element and the track to be read. On the other hand, ΔN determined by the above method is considered to be a value that can serve as an index of the state of existence of ferromagnetic powder in the surface layer region of the magnetic layer. This ΔN is presumed to be a value that is influenced by various factors such as the state of the presence of the binder and the density distribution of the ferromagnetic powder in addition to the orientation state of the ferromagnetic powder in the magnetic layer. It is considered that a magnetic layer whose ΔN is 0.25 or more and 0.40 or less by controlling various factors has a high strength on the surface of the magnetic layer and is difficult to be scraped even if it comes into contact with a reading element. As a result, it is possible to prevent the contact between the magnetic layer surface and the reading element from becoming unstable due to scrapes generated when the magnetic layer surface is scraped, which contributes to suppressing the occurrence of the above-mentioned relative position fluctuation. It is inferred. This contributes to making it possible to apply more suitable waveform equalization processing to each of the reading results obtained by multiple reading elements, and also enables the amount of deviation (track The present inventors believe that this leads to increasing the allowable amount of offset amount).
In addition, as mentioned earlier, the fact that the servo pattern is formed in a shape closer to the designed shape is thought to lead to a larger allowable amount of deviation (track offset amount) that can ensure good playback quality. It will be done. In this regard, the above difference (L _99.9 - L _0.1 ) is an index regarding the shape of the servo pattern, and this difference (L _99.9 - L _0.1 ) may be less than 180 nm. The present inventors believe that this contributes to increasing the allowable amount of deviation (track offset amount) that can ensure good playback quality. The shape of the servo pattern formed on the magnetic layer depends on the shape of the servo pattern (magnetized region) that the servo write head attempts to form on the magnetic layer by applying a magnetic field, and the shape of the servo pattern that is actually formed on the magnetic layer. One possible means for suppressing the deviation from the shape is to improve the performance of the servo write head, specifically, to use a servo write head with a large magnetic field (leakage field). It is also thought that debris is generated when a servo write head forms a servo pattern by applying a magnetic field to the magnetic layer while being in contact with the surface of the magnetic layer. The more these scraps are present between the surface of the magnetic layer and the servo write head, the more unstable the contact state between the surface of the magnetic layer and the servo write head becomes. This causes a discrepancy between the shape of the servo pattern (magnetized region) that the servo write head attempts to form on the magnetic layer by applying a magnetic field, and the shape of the servo pattern that is actually formed on the magnetic layer. The present inventors conjecture that this is the case. On the other hand, the fact that a magnetic layer with a ΔN of 0.25 or more and 0.40 or less is difficult to scrape even when it comes into contact with a servo write head means that a servo pattern with a shape closer to the designed shape can be formed, that is, the above difference The present inventors believe that this contributes to reducing (L _99.9 - L _0.1 ) to 180 nm or less.
However, the above is speculation by the present inventors, and does not limit the present invention in any way.

The magnetic tape will be explained in more detail below.

<ΔN of magnetic layer>
The magnetic layer of the magnetic tape has a ΔN of 0.25 or more and 0.40 or less. From the viewpoint of increasing the allowable amount of deviation (track offset amount) that can ensure good reproduction quality, ΔN is preferably 0.25 or more and 0.35 or less. Specific aspects of the means for adjusting ΔN will be described later.

ΔN is the absolute value of the difference between Nxy and Nz. Nxy is a refractive index measured in the in-plane direction of the magnetic layer, and Nz is a refractive index measured in the thickness direction of the magnetic layer. In one aspect, Nxy>Nz, and in another aspect, Nxy<Nz. From the viewpoint of electromagnetic conversion characteristics of the magnetic tape, it is preferable that Nxy>Nz, and therefore, the difference between Nxy and Nz (Nxy-Nz) is preferably 0.25 or more and 0.40 or less, and 0.25 More preferably, it is 0.35 or less. In one aspect, Nxy can range from 1.50 to 2.50, for example. In one aspect, Nz can range from 1.30 to 2.50, for example. However, in the magnetic tape, ΔN may be in a range of 0.25 or more and 0.40 or less, and Nxy and Nz are not limited to the ranges exemplified above.

Various means for adjusting ΔN explained above will be described later.

<Difference (L _99.9 - L _0.1 )>
The above difference (L _99.9 −L _0.1 ) is 180 nm or less. It is presumed that this also contributes to increasing the allowable amount of deviation (track offset amount) that can ensure good reproduction quality. From the above viewpoint, the difference (L _99.9 −L _0.1 ) is preferably 170 nm or less, more preferably 160 nm or less, and even more preferably 150 nm or less. Further, the difference (L _99.9 −L _0.1 ) can be, for example, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more. However, it is considered that the smaller the value of the difference (L _99.9 - L _0.1 ) is, the better it is in terms of increasing the allowable amount of deviation (track offset amount) that can ensure good playback quality. The difference (L _99.9 −L _0.1 ) may be less than the lower limit exemplified above.

Next, the magnetic layer and the like of the magnetic tape will be further explained.

<Magnetic layer>
(Ferromagnetic powder)
The magnetic layer includes ferromagnetic powder and a binder. As the ferromagnetic powder contained in the magnetic layer, ferromagnetic powders known as ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used. It is preferable to use ferromagnetic powder having a small average particle size from the viewpoint of improving recording density. From this point of view, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, and 30 nm or less. It is even more preferable that it is, even more preferably that it is 25 nm or less, and even more preferably that it is 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, and still more preferably 15 nm or more. is more preferable, and even more preferably 20 nm or more.

-Hexagonal ferrite powder-
A preferred example of the ferromagnetic powder is hexagonal ferrite powder. For details on the hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726A, and Paragraphs 0029 to 0084 of Japanese Patent Application Publication No. 2015-127985 can be referred to.

In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite type crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to a structure to which the most intense diffraction peak belongs in an X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, if the most intense diffraction peak in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to a hexagonal ferrite crystal structure, it is determined that a hexagonal ferrite crystal structure has been detected as the main phase. shall be taken as a thing. When only a single structure is detected by X-ray diffraction analysis, this detected structure is taken as the main phase. The hexagonal ferrite type crystal structure includes at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. The divalent metal atom is a metal atom that can become a divalent cation as an ion, and includes alkaline earth metal atoms such as strontium atom, barium atom, and calcium atom, lead atom, and the like. In the present invention and this specification, hexagonal strontium ferrite powder refers to powder in which the main divalent metal atoms contained are strontium atoms, and hexagonal barium ferrite powder refers to powder in which the main divalent metal atoms contained in this powder are strontium atoms. The divalent metal atom is a barium atom. The main divalent metal atoms are the divalent metal atoms that account for the largest percentage on an atomic percent basis among the divalent metal atoms contained in this powder. However, the divalent metal atoms mentioned above do not include rare earth atoms. A "rare earth atom" in the present invention and herein is selected from the group consisting of scandium atom (Sc), yttrium atom (Y), and lanthanide atom. Lanthanoid atoms include lanthanum atom (La), cerium atom (Ce), praseodymium atom (Pr), neodymium atom (Nd), promethium atom (Pm), samarium atom (Sm), europium atom (Eu), and gadolinium atom (Gd). ), terbium atom (Tb), dysprosium atom (Dy), holmium atom (Ho), erbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu). Ru.

Below, hexagonal strontium ferrite powder, which is one embodiment of hexagonal ferrite powder, will be explained in more detail.

The activation volume of the hexagonal strontium ferrite powder is preferably in the range of 800 to 1600 nm ³ . Finely divided hexagonal strontium ferrite powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm ³ or more, and can also be, for example, 850 nm ³ or more. In addition, from the viewpoint of further improving electromagnetic conversion characteristics, the activated volume of the hexagonal strontium ferrite powder is more preferably 1500 nm ³ or less, even more preferably 1400 nm ³ or less, and 1300 nm ³ or less. is more preferable, it is even more preferable that it is 1200 nm ³ or less, and even more preferably that it is 1100 nm ³ or less. The same applies to the activation volume of hexagonal barium ferrite powder.

"Activation volume" is a unit of magnetization reversal and is an index indicating the magnetic size of a particle. The activation volume described in the present invention and this specification and the anisotropy constant Ku described later are measured using a vibrating sample magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercive force Hc measuring section (measurement Temperature: 23° C.±1° C.), a value determined from the following relational expression between Hc and activation volume V. Note that the unit of the anisotropy constant Ku is 1erg/cc=1.0×10 ⁻¹ J/m ³ .
Hc=2Ku/Ms {1-[(kT/KuV)ln(At/0.693)] ^1/2 }
[In the above formula, Ku: anisotropy constant (unit: J/m ³ ), Ms: saturation magnetization (unit: kA/m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activity volume (unit: cm ³ ), A: spin precession frequency (unit: s ⁻¹ ), t: magnetic field reversal time (unit: s)]

The anisotropy constant Ku can be cited as an index of reduction in thermal fluctuation, in other words, improvement in thermal stability. The hexagonal strontium ferrite powder can preferably have a Ku of 1.8×10 ⁵ J/m ³ or more, more preferably 2.0×10 ⁵ J/m ³ or more. Moreover, Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 ⁵ J/m ³ or less. However, since a higher Ku means higher thermal stability and is preferable, it is not limited to the values exemplified above.

The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are contained at a content (bulk content) of 0.5 to 5.0 at % based on 100 at % iron atoms. In one embodiment, the hexagonal strontium ferrite powder containing rare earth atoms can have rare earth atoms unevenly distributed in the surface layer. In the present invention and this specification, "rare earth atom uneven distribution in the surface layer" refers to the rare earth atom content (hereinafter, "Rare earth atom surface content" or simply "surface layer content" for rare earth atoms) is 100 at.% of iron atoms in the solution obtained by completely dissolving hexagonal strontium ferrite powder with acid. Rare earth atom content (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms),
Rare earth atom surface layer content/rare earth atom bulk content>1.0
This means that the ratio of The rare earth atom content of the hexagonal ferrite powder described below is synonymous with the rare earth atom bulk content. On the other hand, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so the rare earth atom content in the solution obtained by partial dissolution is This is the rare earth atom content in the surface layer of the particles. The fact that the rare earth atom content in the surface layer satisfies the ratio of "rare earth atom surface layer content/rare earth atom bulk content >1.0" means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are present in the surface layer. It means that it is omnipresent (that is, it is present more than inside). In the present invention and this specification, the surface layer portion refers to a partial region from the surface of the particle constituting the hexagonal strontium ferrite powder toward the inside.

When the hexagonal ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atom % based on 100 atom % of iron atoms. It is believed that the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder, which contains rare earth atoms at a bulk content in the above range, contributes to suppressing the reduction in reproduction output during repeated reproduction. Conceivable. This is due to the fact that the hexagonal strontium ferrite powder contains rare earth atoms in the bulk content within the above range, and that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder. It is presumed that this is because it can increase the The higher the value of the anisotropy constant Ku, the more the phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuations, it is possible to suppress a decrease in reproduction output during repeated reproduction. The uneven distribution of rare earth atoms in the particle surface of hexagonal strontium ferrite powder contributes to stabilizing the spin of iron (Fe) sites in the crystal lattice in the surface layer, which increases the anisotropy constant Ku. It is speculated that this will increase.
In addition, it is assumed that using hexagonal strontium ferrite powder, which has rare earth atoms unevenly distributed in the surface layer, as the ferromagnetic powder for the magnetic layer also contributes to suppressing the surface of the magnetic layer from being scraped by sliding with the magnetic head. Ru. That is, it is surmised that the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer may also contribute to improving the running durability of the magnetic tape. This is due to the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder, which improves the interaction between the particle surface and the organic substances (e.g. binders and/or additives) contained in the magnetic layer. It is presumed that this is because the magnetic layer contributes to the strength of the magnetic layer, and as a result, the strength of the magnetic layer is improved.
From the viewpoint of further suppressing the decline in reproduction output during repeated reproduction and/or further improving running durability, the rare earth atom content (bulk content) is in the range of 0.5 to 4.5 at%. It is more preferably in the range of 1.0 to 4.5 atom %, even more preferably in the range of 1.5 to 4.5 atom %.

The above bulk content is the content determined by completely melting the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the atomic content refers to the bulk content determined by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one kind of rare earth atoms, or may contain two or more kinds of rare earth atoms. The above-mentioned bulk content when two or more types of rare earth atoms are included is calculated for the total of two or more types of rare earth atoms. This point also applies to other components in the present invention and this specification. That is, unless otherwise specified, one kind of a certain component may be used, or two or more kinds thereof may be used. When two or more types are used, the content or content rate refers to the total of the two or more types.

When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms contained may be at least one kind of rare earth atoms. Preferred rare earth atoms from the viewpoint of further suppressing a decrease in reproduction output during repeated reproduction include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, with neodymium atoms, samarium atoms, and yttrium atoms being more preferred; Atom is more preferred.

In the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, it is sufficient that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for a hexagonal strontium ferrite powder that has rare earth atoms unevenly distributed in the surface layer, the surface layer content of rare earth atoms determined by partial melting under the melting conditions described below and the rare earth content determined by completely melting under the melting conditions described below. The ratio of atoms to the bulk content, "surface layer content/bulk content" is more than 1.0, and can be 1.5 or more. When the "surface layer content ratio/bulk content ratio" is larger than 1.0, it means that rare earth atoms are unevenly distributed in the surface layer (that is, more present than in the interior) in the particles that make up the hexagonal strontium ferrite powder. do. In addition, the ratio of the surface layer content of rare earth atoms determined by partial dissolution under the dissolution conditions described below and the bulk content of rare earth atoms determined by total dissolution under the dissolution conditions described below, ``surface layer content/ Bulk content" can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, it is sufficient that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above "surface layer content/bulk content" is sufficient. The "rate" is not limited to the illustrated upper or lower limits.

Partial and total dissolution of hexagonal strontium ferrite powder will be explained below. For hexagonal strontium ferrite powders that are present as powders, the partially dissolved and fully dissolved sample powders are taken from the same lot of powder. On the other hand, regarding the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic tape, part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial melting, and the other part is subjected to total melting. The hexagonal strontium ferrite powder can be taken out from the magnetic layer by, for example, the method described in paragraph 0032 of JP-A-2015-91747.
The above-mentioned partial dissolution means that the hexagonal strontium ferrite powder is dissolved to such an extent that residual hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, by partial dissolution, it is possible to dissolve a region of 10 to 20 mass % of the particles constituting the hexagonal strontium ferrite powder, assuming that the entire particle is 100 mass %. On the other hand, the above-mentioned complete dissolution means that the hexagonal strontium ferrite powder is dissolved to a state where no residual hexagonal strontium ferrite powder is visually confirmed in the liquid upon completion of dissolution.
The above-mentioned partial dissolution and measurement of the surface layer content are performed, for example, by the following method. However, the dissolution conditions such as the amount of sample powder described below are merely examples, and any dissolution conditions that allow partial dissolution and complete dissolution can be adopted as desired.
A container (for example, a beaker) containing 12 mg of sample powder and 10 ml of 1 mol/L hydrochloric acid is held on a hot plate at a set temperature of 70° C. for 1 hour. The obtained solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained is performed using an inductively coupled plasma (ICP) analyzer. In this way, the content of rare earth atoms in the surface layer relative to 100 atom % of iron atoms can be determined. When multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. This point also applies to the measurement of bulk content.
On the other hand, the measurement of the total dissolution and bulk content is performed, for example, by the following method.
A container (for example, a beaker) containing 12 mg of sample powder and 10 ml of 4 mol/L hydrochloric acid is held on a hot plate at a set temperature of 80° C. for 3 hours. Thereafter, it is possible to determine the bulk content relative to 100 atom % of iron atoms by performing the same steps as the above-described partial dissolution and measurement of the surface layer content.

From the viewpoint of increasing reproduction output when reproducing information recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, a hexagonal strontium ferrite powder that contains rare earth atoms but does not have rare earth atoms unevenly distributed in the surface layer tends to have a significantly lower σs than a hexagonal strontium ferrite powder that does not contain rare earth atoms. On the other hand, a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer is considered to be preferable in order to suppress such a large decrease in σs. In one aspect, σs of the hexagonal strontium ferrite powder can be 45 A·m ² /kg or more, and can also be 47 A·m ² /kg or more. On the other hand, from the viewpoint of noise reduction, σs is preferably 80 A·m ² /kg or less, more preferably 60 A·m ² /kg or less. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, mass magnetization σs is a value measured at a magnetic field strength of 1194 kA/m (15 kOe).

Regarding the content of the constituent atoms (bulk content) of the hexagonal ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atom % based on 100 atom % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder may contain only strontium atoms as divalent metal atoms. In another aspect, the hexagonal strontium ferrite powder can also contain one or more other divalent metal atoms in addition to strontium atoms. For example, it can contain barium atoms and/or calcium atoms. When divalent metal atoms other than strontium atoms are included, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder are, for example, 0.05 to 5, respectively, relative to 100 at% of iron atoms. It can be in the range of .0 at.%.

As the crystal structure of hexagonal ferrite, magnetoplumbite type (also called "M type"), W type, Y type, and Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. Crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder may have a single crystal structure or two or more types of crystal structures detected by X-ray diffraction analysis. For example, in one embodiment, the hexagonal strontium ferrite powder can have only an M-type crystal structure detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by the composition formula AFe ₁₂ O ₁₉ . Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is M type, A is only a strontium atom (Sr), or if A contains multiple divalent metal atoms, As mentioned above, strontium atoms (Sr) account for the largest amount on an atomic percent basis. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite, and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms, and oxygen atoms, and may also contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % with respect to 100 atomic % of iron atoms. From the viewpoint of further suppressing the reduction in playback output during repeated playback, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is 100 iron atoms. %, it is preferably 10.0 atom % or less, more preferably in the range of 0 to 5.0 atom %, and may be 0 atom %. That is, in one embodiment, the hexagonal strontium ferrite powder may not contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed in atomic % above is the content of each atom (unit: mass %) obtained by completely melting the hexagonal strontium ferrite powder, and is converted to the value expressed in atomic % using the atomic weight of each atom. It can be calculated by converting. Furthermore, in the present invention and this specification, "not containing" an atom means that the content thereof as measured by an ICP analyzer after being completely dissolved is 0% by mass. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above-mentioned "does not contain" is used to mean that it is contained in an amount below the detection limit of the ICP analyzer. In one embodiment, the hexagonal strontium ferrite powder can be free of bismuth atoms (Bi).

-Metal powder-
A preferable specific example of the ferromagnetic powder is a ferromagnetic metal powder. For details of the ferromagnetic metal powder, reference can be made to, for example, paragraphs 0137 to 0141 of JP-A No. 2011-216149 and paragraphs 0009 to 0023 of JP-A No. 2005-251351.

-ε-Iron oxide powder-
A preferred example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as the main phase by X-ray diffraction analysis. For example, if the most intense diffraction peak in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the ε-iron oxide type crystal structure, it is assumed that the ε-iron oxide type crystal structure has been detected as the main phase. shall judge. Known methods for producing ε-iron oxide powder include a method for producing it from goethite, a reverse micelle method, and the like. All of the above manufacturing methods are publicly known. Further, regarding a method for producing ε-iron oxide powder in which a part of Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, Rh, etc., see, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206 etc. can be referred to. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the method mentioned above.

The activated volume of the ε-iron oxide powder is preferably in the range of 300 to 1500 nm ³ . Finely divided ε-iron oxide powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activated volume of the ε-iron oxide powder is preferably 300 nm ³ or more, and can also be, for example, 500 nm ³ or more. Further, from the viewpoint of further improving electromagnetic conversion characteristics, the activated volume of the ε-iron oxide powder is more preferably 1400 nm ³ or less, even more preferably 1300 nm ³ or less, and 1200 nm ³ or less. is more preferable, and even more preferably 1100 nm ³ or less.

The anisotropy constant Ku can be cited as an index of reduction in thermal fluctuation, in other words, improvement in thermal stability. The ε-iron oxide powder can preferably have a Ku of 3.0×10 ⁴ J/m ³ or more, more preferably 8.0×10 ⁴ J/m ³ or more. Further, Ku of the ε-iron oxide powder can be, for example, 3.0×10 ⁵ J/m ³ or less. However, since a higher Ku means higher thermal stability, which is preferable, it is not limited to the values exemplified above.

From the viewpoint of increasing reproduction output when reproducing information recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, in one aspect, the σs of the ε-iron oxide powder can be 8 A·m ² /kg or more, and can also be 12 A·m ² /kg or more. On the other hand, from the viewpoint of noise reduction, σs of the ε-iron oxide powder is preferably 40 A·m ² /kg or less, more preferably 35 A·m ² /kg or less.

In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powder is a value measured by the following method using a transmission electron microscope.
The powder is photographed using a transmission electron microscope at a magnification of 100,000 times and printed on photographic paper at a total magnification of 500,000 times to obtain a photograph of the particles constituting the powder. Select the target particle from the obtained particle photo, trace the outline of the particle with a digitizer, and measure the size of the particle (primary particle). Primary particles refer to independent particles without agglomeration.
The above measurements are performed on 500 randomly extracted particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is defined as the average particle size of the powder. As the transmission electron microscope, for example, a transmission electron microscope model H-9000 manufactured by Hitachi may be used. Furthermore, the particle size can be measured using known image analysis software, such as Carl Zeiss image analysis software KS-400. Unless otherwise specified, the average particle size shown in the examples below was measured using a transmission electron microscope H-9000 model manufactured by Hitachi as a transmission electron microscope and image analysis software KS-400 manufactured by Carl Zeiss as image analysis software. It is a value. In the present invention and herein, powder refers to a collection of particles. For example, ferromagnetic powder means a collection of multiple ferromagnetic particles. Furthermore, an aggregate of multiple particles is not limited to an embodiment in which the particles constituting the aggregate are in direct contact with each other, but also includes an embodiment in which a binder, an additive, etc., which will be described later, are interposed between the particles. Ru. The term particle is sometimes used to refer to powder.

As a method for collecting sample powder from a magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of JP-A No. 2011-048878 can be adopted.

In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is as follows:
(1) If the particle is needle-shaped, spindle-shaped, columnar (however, the height is larger than the maximum major axis of the bottom surface), etc., it is expressed by the length of the major axis that makes up the particle, that is, the major axis length,
(2) If it is plate-shaped or columnar (however, the thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is expressed by the maximum major axis of the plate surface or bottom surface,
(3) If the particle is spherical, polyhedral, unspecified, etc., and the long axis constituting the particle cannot be identified from the shape, it is expressed by an equivalent circle diameter. The equivalent circle diameter refers to what is determined by the circular projection method.

In addition, the average acicular ratio of the powder can be determined by measuring the short axis length of the particles in the above measurement, determining the value of (major axis length / short axis length) of each particle, and calculating the average acicular ratio of the 500 particles. Refers to the arithmetic mean of the values obtained for the particles. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the case of (1) in the above particle size definition, and the thickness or height in the case of (2). In the case of (3), there is no distinction between the major axis and the minor axis, so (major axis length/minor axis length) is regarded as 1 for convenience.
Unless otherwise specified, when the particle shape is specific, for example, in the case of the above definition (1) of particle size, the average particle size is the average major axis length, and in the case of the same definition (2), the average particle size is This is the average plate diameter. In the case of the same definition (3), the average particle size is the average diameter (also referred to as average particle diameter or average particle diameter).

In one embodiment, the ferromagnetic particles constituting the ferromagnetic powder included in the magnetic layer can have a plate shape. In the following, a ferromagnetic powder composed of plate-shaped ferromagnetic particles will be referred to as a plate-shaped ferromagnetic powder. The average platelet ratio of the plate-like ferromagnetic powder can preferably range from 2.5 to 5.0. The average plate ratio is the arithmetic mean of (maximum major axis/thickness or height) in the case of definition (2) above. As the average plate ratio increases, the uniformity of the orientation state of the ferromagnetic particles constituting the plate-shaped ferromagnetic powder tends to increase through orientation treatment, and the value of ΔN tends to increase.

The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass. Components other than the ferromagnetic powder of the magnetic layer are at least a binder, and optionally one or more additional additives may be included. It is preferable that the filling rate of ferromagnetic powder in the magnetic layer is high from the viewpoint of improving recording density.

(Binder, hardening agent)
The above magnetic tape is a coated magnetic tape and contains a binder in the magnetic layer. A binder is one or more resins. The resin may be a homopolymer or a copolymer. Binders contained in the magnetic layer include polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, One selected from polyvinyl alkyl resins such as polyvinyl acetal and polyvinyl butyral can be used alone, or a plurality of resins can be used in combination. Among these, preferred are polyurethane resins, acrylic resins, cellulose resins and vinyl chloride resins. These resins can also be used as a binder in the nonmagnetic layer and/or back coat layer described below. Regarding the above binders, reference can be made to paragraphs 0029 to 0031 of JP-A No. 2010-24113. Further, the binder may be a radiation curable resin such as an electron beam curable resin. Regarding the radiation-curable resin, paragraphs 0044 to 0045 of JP-A No. 2011-048878 can be referred to.
The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as a weight average molecular weight. The weight average molecular weight in the present invention and this specification is a value determined by converting a value measured by gel permeation chromatography (GPC) into polystyrene. As measurement conditions, the following conditions can be mentioned. The weight average molecular weight shown in the Examples below is a value determined by converting the value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh Corporation)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm ID (Inner Diameter) x 30.0cm)
Eluent: Tetrahydrofuran (THF)

In one aspect, a binder containing an acidic group can be used as the binder. In the present invention and the present specification, the term "acidic group" shall be used to include a group capable of dissociating into an anion by releasing H ⁺ in water or a water-containing solvent (aqueous solvent), and a salt form thereof. . Specific examples of acidic groups include sulfonic acid groups, sulfuric acid groups, carboxy groups, phosphoric acid groups, and salt forms thereof. For example, the salt form of a sulfonic acid group (-SO ₃ H) is a group represented by -SO ₃ M, where M represents an atom that can become a cation (for example, an alkali metal atom, etc.) in water or an aqueous solvent. means. This point also applies to the salt forms of the various groups mentioned above. An example of a binder containing an acidic group includes, for example, a resin containing at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof (eg, polyurethane resin, vinyl chloride resin, etc.). However, the resin contained in the magnetic layer is not limited to these resins. Further, in the binder containing acidic groups, the acidic group content can be in the range of, for example, 20 to 500 eq/ton. The content of various functional groups such as acidic groups contained in the resin can be determined by known methods depending on the type of functional group. The value of ΔN tends to increase as a binder with a higher content of acidic groups is used. The binder can be used in the composition for forming a magnetic layer in an amount of, for example, 1.0 to 30.0 parts by mass, preferably 1.0 to 30.0 parts by mass, based on 100.0 parts by mass of ferromagnetic powder. It can be used in an amount of 20.0 parts by weight. The value of ΔN tends to increase as the amount of binder used in the ferromagnetic powder increases.

A curing agent can also be used in conjunction with a resin that can be used as a binder. In one embodiment, the curing agent can be a thermosetting compound, which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating, and in another embodiment, a photocuring compound, in which a curing reaction (crosslinking reaction) proceeds by light irradiation. It can be a chemical compound. As a curing reaction progresses during the magnetic layer forming process, at least a portion of the curing agent may be contained in the magnetic layer in a reacted (crosslinked) state with other components such as a binder. This point also applies to layers formed using the composition when the composition used to form the other layer contains a curing agent. Preferred curing agents are thermosetting compounds, with polyisocyanates being preferred. For details of the polyisocyanate, paragraphs 0124 to 0125 of JP-A No. 2011-216149 can be referred to. The curing agent is contained in the magnetic layer forming composition in an amount of, for example, 0 to 80.0 parts by mass based on 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of the magnetic layer. It can be used in amounts of parts by weight.

(Additive)
The magnetic layer contains a ferromagnetic powder and a binder, and may contain one or more additives as necessary. Examples of the additives include the above-mentioned curing agents. In addition, examples of additives included in the magnetic layer include non-magnetic powder (for example, inorganic powder, carbon black, etc.), lubricant, dispersant, dispersion aid, fungicide, antistatic agent, antioxidant, etc. I can do it. Examples of the non-magnetic powder include non-magnetic powder that can function as an abrasive, and non-magnetic powder that can function as a protrusion-forming agent that forms protrusions that protrude moderately on the surface of the magnetic layer (for example, non-magnetic colloidal particles). etc.) etc. Note that the average particle size of colloidal silica (silica colloidal particles) shown in the Examples below is a value determined by the method described in paragraph 0015 of JP 2011-048878A as the method for measuring the average particle size. . The additives can be used in any amount by appropriately selecting commercially available products or by manufacturing them by known methods, depending on the desired properties. Examples of additives that can be used in the magnetic layer containing an abrasive include the dispersants described in paragraphs 0012 to 0022 of JP-A No. 2013-131285 as dispersants for improving the dispersibility of the abrasive. be able to. Further, for example, regarding lubricants, paragraphs 0030 to 0033, 0035, and 0036 of JP 2016-126817A can be referred to. The nonmagnetic layer may contain a lubricant. Regarding the lubricant that can be included in the nonmagnetic layer, paragraphs 0030, 0031, 0034, 0035, and 0036 of JP 2016-126817A can be referred to. Regarding the dispersant, paragraphs 0061 and 0071 of JP 2012-133837A can be referred to. The dispersant may be included in the nonmagnetic layer. Regarding the dispersant that can be included in the nonmagnetic layer, paragraph 0061 of JP 2012-133837A can be referred to.

The magnetic layer described above can be provided directly on the surface of the nonmagnetic support or indirectly via the nonmagnetic layer.

<Nonmagnetic layer>
Next, the nonmagnetic layer will be explained. The magnetic tape may have a magnetic layer directly on the non-magnetic support, or may have a non-magnetic layer containing non-magnetic powder and a binder between the non-magnetic support and the magnetic layer. good. The nonmagnetic powder used in the nonmagnetic layer may be an inorganic powder or an organic powder. Further, carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are available as commercial products, and can also be produced by known methods. For details thereof, paragraphs 0146 to 0150 of JP-A No. 2011-216149 can be referred to. Regarding carbon black that can be used in the nonmagnetic layer, paragraphs 0040 to 0041 of JP-A No. 2010-24113 can also be referred to. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass.

For other details such as the binder and additives of the nonmagnetic layer, known techniques regarding nonmagnetic layers can be applied. Further, for example, regarding the type and content of the binder, the type and content of the additive, and the like, known techniques regarding the magnetic layer can also be applied.

The nonmagnetic layer of the magnetic tape includes, along with nonmagnetic powder, a substantially nonmagnetic layer containing a small amount of ferromagnetic powder, for example as an impurity or intentionally. Here, a substantially non-magnetic layer means that this layer has a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA/m (100 Oe) or less, or a residual magnetic flux density of 10 mT or less. A layer having a coercive force of 7.96 kA/m (100 Oe) or less. Preferably, the nonmagnetic layer has no residual magnetic flux density and no coercive force.

<Nonmagnetic support>
Next, the nonmagnetic support will be explained. Examples of the nonmagnetic support (hereinafter also simply referred to as "support") include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be subjected to corona discharge, plasma treatment, adhesive treatment, heat treatment, etc. in advance.

<Back coat layer>
The above magnetic tape may or may not have a back coat layer containing nonmagnetic powder and a binder on the surface side of the nonmagnetic support opposite to the surface side having the magnetic layer. The back coat layer preferably contains one or both of carbon black and inorganic powder. Regarding the binder contained in the back coat layer and various additives that may be optionally included, known techniques related to the back coat layer can be applied, and known techniques related to the formulation of the magnetic layer and/or nonmagnetic layer can be applied. You can also do it. For example, the descriptions in paragraphs 0018 to 0020 of JP-A No. 2006-331625 and in column 4, line 65 to column 5, line 38 of U.S. Patent No. 7,029,774 can be referred to regarding the back coat layer. .

<Various thicknesses>
The thickness of the nonmagnetic support is, for example, 3.0 to 80.0 μm, preferably 3.0 to 50.0 μm, and more preferably 3.0 to 10.0 μm.

The thickness of the magnetic layer can be optimized depending on the saturation magnetization, head gap length, recording signal band, etc. of the magnetic head used. The thickness of the magnetic layer is generally 10 nm to 100 nm, preferably 20 to 90 nm, more preferably 30 to 70 nm from the viewpoint of high density recording. It is sufficient that there is at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic properties, and a structure related to a known multilayer magnetic layer can be applied. The thickness of the magnetic layer when it is separated into two or more layers is the total thickness of these layers.

The thickness of the nonmagnetic layer is, for example, 0.1 to 1.5 μm, preferably 0.1 to 1.0 μm.

The thickness of the back coat layer is preferably 0.9 μm or less, more preferably 0.1 to 0.7 μm.

The thickness of each layer and the nonmagnetic support is determined by exposing a cross section in the thickness direction of the magnetic tape using a known method such as an ion beam or a microtome, and then using a scanning transmission electron microscope (STEM) on the exposed cross section. ) shall be used to perform cross-sectional observation. For a specific example of the thickness measurement method, reference can be made to the description regarding the thickness measurement method in Examples described later.

<Method for manufacturing magnetic tape>
<<Preparation of magnetic tape on which servo patterns are formed>>
(Preparation of composition for forming each layer)
The process of preparing a composition for forming a magnetic layer, a nonmagnetic layer, or a backcoat layer usually includes at least a kneading process, a dispersion process, and a mixing process provided before and after these processes as necessary. Each individual process may be divided into two or more stages. The components used to prepare each layer-forming composition may be added at the beginning or middle of any step. As the solvent, one or more of various solvents commonly used in manufacturing coated magnetic recording media can be used. Regarding the solvent, reference can be made to, for example, paragraph 0153 of JP-A No. 2011-216149. Further, the individual components may be added in divided portions in two or more steps. For example, the binder may be added in portions during the kneading step, the dispersion step, and the mixing step for adjusting the viscosity after dispersion. In order to manufacture the above magnetic tape, conventional and well-known manufacturing techniques can be used in various steps. In the kneading step, it is preferable to use an open kneader, continuous kneader, pressure kneader, extruder, or other device with strong kneading power. For details of these kneading treatments, refer to JP-A-1-106338 and JP-A-1-79274. A known disperser can be used. Further, the ferromagnetic powder and the abrasive can also be separately dispersed. More specifically, separate dispersion refers to the process of mixing an abrasive liquid containing an abrasive and a solvent (but substantially free of ferromagnetic powder) with a magnetic liquid containing ferromagnetic powder, a solvent, and a binder. This is a method for preparing a composition for forming a magnetic layer. The above phrase "substantially free of ferromagnetic powder" means that ferromagnetic powder is not added as a component of the polishing solution, and only a trace amount of ferromagnetic powder is added as an unintentionally mixed impurity. shall be allowed to exist. Regarding ΔN, the value of ΔN tends to increase as the conditions for dispersing the magnetic liquid are strengthened. For example, the value of ΔN tends to increase as the dispersion time of the magnetic liquid increases. This is because the longer the dispersion time of the magnetic liquid, the higher the dispersibility of the ferromagnetic powder in the coating layer of the magnetic layer forming composition, and the more uniform the orientation state of the ferromagnetic particles constituting the ferromagnetic powder is by the orientation treatment. This is thought to be because there is a tendency for the amount to increase. Furthermore, the longer the dispersion time when mixing and dispersing the various components of the composition for forming a nonmagnetic layer, the greater the value of ΔN tends to be. The dispersion time of the magnetic liquid and the dispersion time of the composition for forming a nonmagnetic layer may be set so as to realize ΔN of 0.25 or more and 0.40 or less.
At any stage of preparing each layer-forming composition, filtration may be performed by a known method. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter with a pore size of 0.01 to 3 μm (eg, a glass fiber filter, a polypropylene filter, etc.) can be used.

(Coating process)
The magnetic layer can be formed by, for example, directly applying the composition for forming a magnetic layer onto a non-magnetic support, or by applying the composition in a multilayer manner sequentially or simultaneously with the composition for forming a non-magnetic layer. The back coat layer can be formed by applying a back coat layer forming composition to the side of the nonmagnetic support opposite to the side having the magnetic layer (or where the magnetic layer will be provided later). Furthermore, the coating process for forming each layer can be performed in two or more stages. For example, in one embodiment, the magnetic layer forming composition can be applied in two or more steps. In this case, drying treatment may or may not be performed between the two stages of the coating process. Furthermore, an orientation treatment may or may not be performed between the two stages of coating steps. For details of coating for forming each layer, reference can also be made to paragraph 0066 of JP-A No. 2010-231843. Furthermore, known techniques can be applied to the drying process after applying each layer-forming composition. Regarding the composition for forming a magnetic layer, a coating layer formed by applying the composition for forming a magnetic layer (hereinafter also referred to as a "coating layer of the composition for forming a magnetic layer" or simply "coating layer") The value of ΔN tends to increase as the drying temperature decreases. The drying temperature can be, for example, the ambient temperature at which the drying process is performed, and may be set so that ΔN of 0.25 or more and 0.40 or less can be achieved.

(Other processes)
Regarding various other processes for manufacturing magnetic tape, reference can be made to paragraphs 0067 to 0070 of JP-A No. 2010-231843.
For example, it is preferable to perform orientation treatment on the coating layer of the composition for forming a magnetic layer while the coating layer is in a wet state. From the viewpoint of ease of achieving ΔN of 0.25 or more and 0.40 or less, the orientation treatment is performed by arranging the magnet so that the magnetic field is applied perpendicularly to the surface of the coating layer of the magnetic layer forming composition. (ie, vertical alignment treatment) is preferable. The strength of the magnetic field during the orientation process may be set so that ΔN of 0.25 or more and 0.40 or less can be achieved. Further, when the coating process of the magnetic layer forming composition is performed in two or more coating steps, it is preferable to carry out an alignment treatment after at least the last coating process, and more preferably to carry out a vertical alignment treatment. For example, when forming a magnetic layer by a two-step coating process, a drying process is performed without performing an orientation treatment after the first coating process, and then the coating layer formed in the second coating process is Orientation treatment can be performed using the following methods. Regarding the alignment treatment, various known techniques such as the one described in paragraph 0052 of JP-A No. 2010-24113 can be applied. For example, the vertical alignment process can be performed by a known method such as a method using magnets with different polarities facing each other. In the orientation zone, the drying speed of the coating layer can be controlled by the temperature and air volume of the drying air and/or the transport speed of the magnetic tape in the orientation zone. Furthermore, the coating layer may be pre-dried before being transported to the orientation zone.
Furthermore, calendering can be carried out at any stage after drying the coating layer of the composition for forming a magnetic layer. For the conditions of calendar processing, for example, paragraph 0026 of Japanese Patent Laid-Open No. 2010-231843 can be referred to. The value of ΔN tends to increase as the calender temperature (surface temperature of the calender roll) increases. The calendar temperature may be set so that ΔN of 0.25 or more and 0.40 or less can be achieved.

<<Formation of servo pattern>>
The magnetic tape has a timing-based servo pattern in the magnetic layer. An example of the arrangement of a region (servo band) in which a timing-based servo pattern is formed and a region sandwiched between two servo bands (data band) is shown in FIG. An example of the arrangement of timing-based servo patterns is shown in FIG. Specific examples of the shapes of timing-based servo patterns are shown in FIGS. 15 to 17 and 19 to 21. However, the arrangement examples and/or shapes shown in each drawing are illustrative, and the servo patterns, servo bands, and data bands may be formed and arranged in a shape and arrangement according to the system of the magnetic tape device (drive). Further, regarding the shape and arrangement of the timing base servo pattern, for example, FIG. 4.FIG. 5.FIG. 6. FIG. 9.FIG. 17, FIG. Known techniques such as the arrangement example illustrated in No. 20 can be applied without any restriction.

The servo pattern can be formed by magnetizing a specific region of the magnetic layer with a servo write head mounted on a servo writer. In a timing-based servo system, for example, a servo element reads a pair of mutually non-parallel servo patterns (also called "servo stripes") that are arranged continuously in the longitudinal direction of a magnetic tape, thereby generating a servo signal. is obtained.

In one aspect, as disclosed in Japanese Patent Application Laid-open No. 2004-318983, each servo band includes information indicating the number of the servo band (“servo band ID (identification)” or “UDIM (Unique Data Band Identification Method)”). (also called "information") is embedded. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo patterns in the servo band so that its position is relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the way in which a specific one of a plurality of pairs of servo patterns is shifted is changed for each servo band. As a result, the recorded servo band ID becomes unique for each servo band, and therefore, just by reading one servo band with a servo element, that servo band can be uniquely identified.

Note that as a method for uniquely specifying a servo band, there is also a method using a staggered method as shown in ECMA (European Computer Manufacturers Association)-319. In this staggered method, a plurality of groups of non-parallel servo patterns (servo stripes) arranged consecutively in the longitudinal direction of the magnetic tape are recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. do. This combination of shifting between adjacent servo bands is unique on the entire magnetic tape, making it possible to uniquely identify a servo band when reading a servo pattern using two servo elements. It has become.

Furthermore, as shown in ECMA-319, each servo band is usually embedded with information indicating the position in the longitudinal direction of the magnetic tape (also called "LPOS (Longitudinal Position) information"). Like the UDIM information, this LPOS information is also recorded by shifting the positions of a pair of servo patterns in the longitudinal direction of the magnetic tape. However, unlike the UDIM information, in this LPOS information, the same signal is recorded in each servo band.

It is also possible to embed other information different from the above-mentioned UDIM information and LPOS information into the servo band. In this case, the embedded information may be different for each servo band, such as UDIM information, or may be common to all servo bands, such as LPOS information.
Further, as a method of embedding information in the servo band, it is also possible to employ methods other than those described above. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of pairs of servo patterns.

The servo write head has a pair of gaps corresponding to the pair of servo patterns, equal to the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and by supplying current pulses to the coils, the magnetic field generated in the core can cause a leakage magnetic field in the pair of gaps. When forming a servo pattern, by inputting a current pulse while running the magnetic tape over the servo write head, a magnetic pattern corresponding to a pair of gaps is transferred onto the magnetic tape, thereby forming a servo pattern. I can do it. The width of each gap can be appropriately set depending on the density of the servo pattern to be formed. The width of each gap can be set to, for example, 1 μm or less, 1 to 10 μm, or 10 μm or more.

Before forming servo patterns on a magnetic tape, the magnetic tape is usually subjected to demagnetization (erase) processing. This erasing process can be performed by applying a uniform magnetic field to the magnetic tape using a DC magnet or an AC magnet. Erase processing includes DC (Direct Current) erase and AC (Alternating Current) erase. AC erase is performed by gradually lowering the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, DC erasing is performed by applying a unidirectional magnetic field to the magnetic tape. There are two more methods for DC erase. The first method is horizontal DC erase, which applies a unidirectional magnetic field along the length of the magnetic tape. The second method is vertical DC erase, which applies a unidirectional magnetic field along the thickness of the magnetic tape. The erase process may be performed on the entire magnetic tape, or may be performed on each servo band of the magnetic tape.

The direction of the magnetic field of the servo pattern to be formed is determined depending on the erase direction. For example, when a magnetic tape is subjected to horizontal DC erasing, the servo pattern is formed such that the direction of the magnetic field is opposite to the erasing direction. Thereby, the output of the servo signal obtained by reading the servo pattern can be increased. As shown in Japanese Patent Application Laid-open No. 2012-53940, when a pattern is transferred using the above-mentioned gap to a magnetic tape that has been vertically DC erased, the servo pattern obtained by reading the formed servo pattern is The signal will be in the form of a unipolar pulse. On the other hand, when a pattern is transferred onto a horizontally DC erased magnetic tape using the gap, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

The magnetic tape described above is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is mounted in a magnetic tape device.

[Magnetic tape cartridge]
One aspect of the present invention relates to a magnetic tape cartridge including the above magnetic tape.

The details of the magnetic tape included in the magnetic tape cartridge are as described above.

In a magnetic tape cartridge, a magnetic tape is generally housed inside a cartridge main body in a state where it is wound onto a reel. The reel is rotatably provided inside the cartridge body. As magnetic tape cartridges, single-reel type magnetic tape cartridges having one reel inside the cartridge body and twin-reel type magnetic tape cartridges having two reels inside the cartridge body are widely used. When a single-reel magnetic tape cartridge is inserted into a magnetic tape device (drive) for recording and/or reproducing information (magnetic signals) on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and inserted into the drive. It is wound onto the reel on the side. A magnetic head is arranged on the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed out and taken up between a reel on the magnetic tape cartridge side (supply reel) and a reel on the drive side (take-up reel). During this time, the magnetic head and the surface of the magnetic layer of the magnetic tape come into contact and slide, thereby recording and/or reproducing information. On the other hand, in a twin-reel type magnetic tape cartridge, both a supply reel and a take-up reel are provided inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single reel type or a twin reel type magnetic tape cartridge. The above-mentioned magnetic tape cartridge may be one that includes the magnetic tape according to one aspect of the present invention, and known techniques can be applied to the other components. Further, regarding one aspect of the magnetic tape cartridge, reference can be made to the previous description regarding the magnetic tape cartridge 12 in FIG. 1.

[Magnetic tape device]
One aspect of the present invention is
Including the magnetic tape, a reading element unit, and an extraction section,
The reading element unit has a plurality of reading elements each reading data from a specific track area including a track to be read out of track areas included in the magnetic tape,
The extraction section relates to a magnetic tape device that extracts data originating from the track to be read from the read results by performing waveform equalization processing on each of the read results for each of the read elements. Such a magnetic tape device is as described in detail above.

The present invention will be explained below based on examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, "parts" and "%" described below are based on mass. Further, the steps and evaluations described below were performed in an environment with an ambient temperature of 23° C.±1° C. unless otherwise specified. "eq" described below is equivalent and is a unit that cannot be converted into SI units.

The activation volumes in Table 1 are values determined for each ferromagnetic powder by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

[Preparation of magnetic tape]
<Example 1>
<<Preparation of abrasive liquid>>
3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Kasei Co., Ltd.) to 100.0 parts of alumina powder (HIT-80, manufactured by Sumitomo Chemical Co., Ltd.) with a pregelatinization rate of about 65% and a BET specific surface area of 20 m ² /g. , 31.3 parts of a 32% solution (solvent is a mixed solvent of methyl ethyl ketone and toluene) of SO ₃ Na group-containing polyester polyurethane resin (UR-4800 manufactured by Toyobo Co., Ltd. (SO ₃ Na group: 0.08 meq/g)), As a result, 570.0 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone (mass ratio) of 1:1 was mixed and dispersed for 5 hours using a paint shaker in the presence of zirconia beads. After dispersion, the dispersion liquid and beads were separated using a mesh to obtain an alumina dispersion.

<<Preparation of composition for forming magnetic layer>>
(Magnetic liquid)
Plate-shaped hexagonal barium ferrite powder 100.0 parts Activation volume: see Table 1, average plate ratio: 3.5
SO ₃ Na group-containing polyurethane resin See Table 1 Weight average molecular weight: 70,000, SO ₃ Na group content: See Table 1 Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (abrasive liquid)
6.0 parts of the alumina dispersion prepared above (silica sol (projection forming agent liquid))
Colloidal silica (average particle size: 100 nm) 2.0 parts Methyl ethyl ketone 1.4 parts (other ingredients)
Stearic acid 2.0 parts Butyl stearate 2.0 parts Polyisocyanate (Coronate (registered trademark) manufactured by Tosoh Corporation) 2.5 parts (finishing solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

(Preparation method)
A magnetic liquid was prepared by bead dispersing the various components of the above magnetic liquid in a batch type vertical sand mill using beads as a dispersion medium. Zirconia beads (bead diameter: see Table 1) were used as beads, and bead dispersion was performed for the time listed in Table 1 (magnetic liquid bead dispersion time).
The thus obtained magnetic liquid, the above-mentioned abrasive liquid, silica sol, other components, and finishing additive solvent were mixed and dispersed in beads for 5 minutes, and then treated with a batch-type ultrasonic device (20 kHz, 300 W) for 0.5 minutes (ultrasonic dispersion) was performed. Thereafter, filtration was performed using a filter having a pore size of 0.5 μm to prepare a composition for forming a magnetic layer.

<<Preparation of composition for forming non-magnetic layer>>
Among the various components of the composition for forming a nonmagnetic layer described below, the components excluding stearic acid, butyl stearate, cyclohexanone, and methyl ethyl ketone were dispersed in beads using a batch type vertical sand mill (dispersion media: zirconia beads (bead diameter : 0.1 mm) and dispersion time (see Table 1) to obtain a dispersion. Thereafter, the remaining components were added to the resulting dispersion and stirred using a dissolver stirrer. Next, the obtained dispersion liquid was filtered using a filter (pore size: 0.5 μm) to prepare a composition for forming a nonmagnetic layer.

Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15 μm
Average acicular ratio: 7
BET specific surface area: 52m ² /g
Carbon black 20.0 parts Average particle size: 20nm
Electron beam curable vinyl chloride copolymer 13.0 parts Electron beam curable polyurethane resin 6.0 parts
Stearic acid 1.0 parts Butyl stearate 1.0 parts Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

<<Preparation of composition for forming back coat layer>>
Among the various components of the composition for forming a backcoat layer described below, components excluding stearic acid, butyl stearate, polyisocyanate, and cyclohexanone were kneaded and diluted using an open kneader to obtain a mixed solution. Thereafter, the resulting mixed solution was processed using a horizontal bead mill using zirconia beads with a bead diameter of 1.0 mm at a bead filling rate of 80 volume % and a rotor tip circumferential speed of 10 m/sec for a residence time of 2 minutes per pass. 12 passes of distributed processing were performed. Thereafter, the remaining components were added to the resulting dispersion and stirred using a dissolver stirrer. Next, the obtained dispersion liquid was filtered using a filter (pore size: 1.0 μm) to prepare a composition for forming a back coat layer.

Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average acicular ratio: 7
BET specific surface area: 52m ² /g
Carbon black 20.0 parts Average particle size: 20nm
Vinyl chloride copolymer 13.0 parts Sulfonic acid group-containing polyurethane resin 6.0 parts Phenylphosphonic acid 3.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Polyisocyanate 5.0 parts Cyclohexanone 355.0 parts

<<Preparation of magnetic tape>>
A nonmagnetic layer forming composition was applied onto a biaxially oriented polyethylene naphthalate support and dried, and then irradiated with an electron beam at an accelerating voltage of 125 kV and an energy of 40 kGy to form a nonmagnetic layer. .
A magnetic layer forming composition was applied onto the surface of the formed nonmagnetic layer so that the thickness after drying was 50 nm to form a coating layer. While this coated layer is in a wet state, use magnets with different polarities in an atmosphere at the ambient temperature listed in Table 1 (magnetic layer drying temperature) to perform the process described in the "Formation and orientation of magnetic layer" column in Table 1. A strong magnetic field was applied perpendicularly to the surface of the coated layer to perform vertical alignment and drying to form a magnetic layer.
Thereafter, a composition for forming a back coat layer was applied onto the surface of the support opposite to the surface on which the nonmagnetic layer and the magnetic layer were formed and dried.
Thereafter, using a calender roll consisting only of metal rolls, the conditions of a calendering speed of 80 m/min, a linear pressure of 300 kg/cm (294 kN/m), and a calender temperature (surface temperature of the calender roll) listed in Table 1 are applied. Below, surface smoothing treatment (calendar treatment) was performed.
Thereafter, heat treatment was performed for 36 hours at an ambient temperature of 70°C. After heat treatment, the tape was slit to a width of 1/2 inch (1 inch is 0.0254 meters), and the tape was attached to a device equipped with a device for feeding and winding slit products so that the nonwoven fabric and razor blade were pressed against the surface of the magnetic layer. The surface of the magnetic layer was cleaned using a cleaning device. After that, with the magnetic layer of the obtained magnetic tape demagnetized, a servo write head (leakage magnetic field: 247 kA/m) mounted on a servo writer is used to write a servo pattern (timing-based servo pattern) with an arrangement and shape according to the LTO Ultrium format. pattern) was formed on the magnetic layer. As a result, the magnetic layer of Example 1 has a data band, a servo band, and a guide band arranged in accordance with the LTO Ultrium format in the magnetic layer, and has a servo pattern arranged and shaped in accordance with the LTO Ultrium format on the servo band. Got the tape.

<Example 3, Comparative Examples 1, 3, 5>
A magnetic tape was produced in the same manner as in Example 1 except that the various items shown in Table 1 were changed as shown in Table 1.
In Table 1, in the comparative examples in which "no orientation treatment" is described in the "Formation and Orientation of Magnetic Layer" column, magnetic tapes were produced without performing orientation treatment on the coated layer of the magnetic layer forming composition.

<Comparative example 2>
Hexagonal barium ferrite powder having the activation volume shown in Table 1 was used as the ferromagnetic powder, various conditions were changed as shown in Table 1, and a servo write head with a leakage magnetic field of 366 kA/m was used as the servo write head. A magnetic tape was produced in the same manner as in Example 1 except for the following points.

<Example 2>
After forming a nonmagnetic layer on a biaxially oriented polyethylene naphthalate support in the same manner as in Example 1, a composition for forming a magnetic layer was applied onto the surface of the nonmagnetic layer so that the thickness after drying was 25 nm. A first coating layer was formed. This first coated layer was passed through an atmosphere at the ambient temperature (magnetic layer drying temperature) listed in Table 1 without applying a magnetic field to form a first magnetic layer (no orientation treatment).
Thereafter, a second coating layer was formed by coating the magnetic layer forming composition on the surface of the first magnetic layer so that the thickness after drying was 25 nm. While this second coated layer is in a wet state, the "Formation and Orientation of Magnetic Layer" column of Table 1 is applied using magnets with opposite polarities in an atmosphere at the ambient temperature shown in Table 1 (magnetic layer drying temperature). A magnetic field of the strength described above was applied in a direction perpendicular to the surface of the second coated layer to perform a vertical alignment process and a drying process to form a second magnetic layer.
A magnetic tape was produced in the same manner as in Example 1 except that the multilayer magnetic layer was formed as described above.

<Comparative example 4>
After forming a nonmagnetic layer on a biaxially oriented polyethylene naphthalate support in the same manner as in Example 1, a composition for forming a magnetic layer was applied onto the surface of the nonmagnetic layer so that the thickness after drying was 25 nm. A first coating layer was formed. While this first coated layer is in a wet state, use magnets with different polarities facing each other in an atmosphere at the ambient temperature listed in Table 1 (magnetic layer drying temperature). A magnetic field having the strength described in 1. was applied perpendicularly to the surface of the first coated layer to perform a vertical alignment treatment and a drying treatment to form a first magnetic layer.
Thereafter, a second coating layer was formed by coating the magnetic layer forming composition on the surface of the first magnetic layer so that the thickness after drying was 25 nm. This second coated layer was passed through an atmosphere at the ambient temperature (magnetic layer drying temperature) listed in Table 1 without applying a magnetic field to form a second magnetic layer (no orientation treatment).
A magnetic tape was produced in the same manner as in Example 1 except that the multilayer magnetic layer was formed as described above.

[Evaluation of the physical properties]
(1) Thickness of non-magnetic support and each layer The thickness of the magnetic layer, non-magnetic layer, non-magnetic support and back coat layer of each produced magnetic tape was measured by the following method. As a result of the measurements, the thickness of the magnetic layer was 50 nm, the thickness of the non-magnetic layer was 0.7 μm, the thickness of the non-magnetic support was 5.0 μm, and the thickness of the back coat layer was 0.5 μm for all magnetic tapes. Ta.
The thicknesses of the magnetic layer, nonmagnetic layer, and nonmagnetic support measured here were used for calculating the refractive index below.
(i) Preparation of a sample for cross-sectional observation In accordance with the method described in paragraphs 0193 to 0194 of JP 2016-177851A, the entire area in the thickness direction from the surface on the magnetic layer side to the surface on the back coat layer side of the magnetic tape is prepared. A sample for cross-sectional observation was prepared.
(ii) Thickness measurement The prepared sample was observed by STEM, and a STEM image was taken. This STEM image is a STEM-HAADF (High-Angle Annular Dark Field) image taken at an accelerating voltage of 300 kV and an imaging magnification of 450,000 times, and one image includes the area from the magnetic layer side surface of the magnetic tape to the back coat layer side surface. The image was taken so that the entire area in the thickness direction was included. In the STEM image thus obtained, a straight line connecting both ends of the line segment representing the magnetic layer surface was determined as a reference line representing the magnetic layer side surface of the magnetic tape. For example, when a STEM image is taken with the magnetic layer side of the sample for cross-sectional observation located above the image and the back coat layer side located below, the straight line connecting both ends of the above line segment means that the STEM image is This is a straight line connecting the intersection between the left side of the image (which has a rectangular or square shape) and the line segment, and the intersection between the right side of the STEM image and the line segment. Similarly, a reference line representing the interface between the magnetic layer and the non-magnetic layer, a reference line representing the interface between the non-magnetic layer and the non-magnetic support, a reference line representing the interface between the non-magnetic support and the back coat layer, and a magnetic tape. A reference line representing the surface of the back coat layer was determined.
The thickness of the magnetic layer was determined as the shortest distance from a randomly selected point on the reference line representing the magnetic layer side surface of the magnetic tape to the reference line representing the interface between the magnetic layer and the nonmagnetic layer. Similarly, the thicknesses of the nonmagnetic layer, nonmagnetic support, and back coat layer were determined.

(2) ΔN of magnetic layer
In the following, M-2000U manufactured by Woollam was used as an ellipsometer. Creation and fitting of the two-layer model or the one-layer model were performed using WVASE32 manufactured by Woollam Co., Ltd. as analysis software.
(i) Measurement of refractive index of non-magnetic support A sample for measurement was cut out from each magnetic tape. A fresh cloth is impregnated with fresh methyl ethyl ketone, and the cloth is used to wipe away the back coat layer of the measurement sample to expose the surface of the non-magnetic support. The surface was roughened with sandpaper so that it would not be detected during measurements with an ellipsometer.
After that, an unused cloth was impregnated with fresh methyl ethyl ketone, and the magnetic layer and non-magnetic layer of the measurement sample were wiped off using this cloth, and then the silicon wafer surface and the roughened surface were connected using static electricity. By pasting the measurement sample with the surface of the nonmagnetic support exposed by removing the magnetic layer and nonmagnetic layer (hereinafter referred to as "the surface of the nonmagnetic support on the magnetic layer side") facing upward. placed on a silicon wafer.
Using an ellipsometer, incident light was applied to the magnetic layer side surface of the nonmagnetic support of the measurement sample on the silicon wafer as described above, and Δ and Ψ were measured. Using the obtained measurement values and the thickness of the non-magnetic support determined in (2) above, the refractive index of the non-magnetic support (refractive index in the longitudinal direction, refractive index in the width direction, longitudinal The refractive index in the thickness direction measured by making incident light enter from the direction, and the refractive index in the thickness direction measured by making incident light enter from the width direction) were determined.
(ii) Measurement of refractive index of non-magnetic layer Measurement samples were cut out from each magnetic tape. A fresh cloth is impregnated with fresh methyl ethyl ketone, and the cloth is used to wipe away the back coat layer of the measurement sample to expose the surface of the non-magnetic support. The surface was roughened with sandpaper so that it would not be detected in measurements with a spectroscopic ellipsometer.
After that, soak an unused cloth in fresh methyl ethyl ketone, and use this cloth to lightly wipe the surface of the magnetic layer of the measurement sample to remove the magnetic layer and expose the surface of the non-magnetic layer. Similarly, a measurement sample was placed on a silicon wafer.
The surface of the nonmagnetic layer of the measurement sample on this silicon wafer was measured using an ellipsometer, and spectroscopic ellipsometry was used to determine the refractive index (refractive index in the longitudinal direction, The refractive index in the thickness direction measured by inputting incident light from the longitudinal direction, and the refractive index in the thickness direction measured by inputting incident light from the width direction) were determined.
(iii) Measurement of refractive index of magnetic layer Measurement samples were cut out from each magnetic tape. A fresh cloth is impregnated with fresh methyl ethyl ketone, and the cloth is used to wipe away the back coat layer of the measurement sample to expose the surface of the non-magnetic support. The surface was roughened with sandpaper so that it would not be detected in measurements with a spectroscopic ellipsometer.
Thereafter, a measurement sample was placed on a silicon wafer in the same manner as in (i) above.
The surface of the magnetic layer of the measurement sample on the silicon wafer was measured using an ellipsometer, and the refractive index (refractive index Nx in the longitudinal direction, Nx in the width direction, The refractive index Ny, the refractive index Nz ₁ in the thickness direction measured by entering incident light from the longitudinal direction, and the refractive index Nz ₂ in the thickness direction measured by entering incident light from the width direction were determined. From the obtained values, Nxy and Nz were obtained, and furthermore, the absolute value ΔN of the difference between them was obtained. For both the magnetic tapes of the example and the comparative example, the determined Nxy was a larger value than Nz (ie, Nxy>Nz).

(3) Vertical squareness ratio (SQ)
The vertical squareness ratio of the magnetic tape is the squareness ratio measured in the vertical direction of the magnetic tape. The "perpendicular direction" described in relation to the squareness ratio refers to a direction perpendicular to the surface of the magnetic layer. For each of the magnetic tapes of Examples and Comparative Examples, an external magnetic field was applied to the magnetic tape using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a measurement temperature of 23°C ± 1°C with a maximum external magnetic field of 1194 kA/m ( The vertical squareness ratio was determined by sweeping under the conditions of 15 kOe) and a scan speed of 4.8 kA/m/sec (60 Oe/sec). The measured value is a value after demagnetizing field correction, and is obtained by subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. In one embodiment, the vertical squareness ratio of the magnetic tape is preferably 0.60 or more and 1.00 or less. Also, in one aspect, the vertical squareness ratio of the magnetic tape can be, for example, 0.90 or less, 0.85 or less, or 0.80 or less, or can exceed these values.

(4) Difference (L _99.9 - L _0.1 )
For each magnetic tape of Examples and Comparative Examples, the difference (L _99.9 - L _0.1 ) was determined by the following method.
Using a Bruker Dimension 3100 in frequency modulation mode as a magnetic force microscope and a Nanoworld SSS-MFMR (nominal radius of curvature 15 nm) as a probe, a 90 μm x 90 μm sample of the magnetic layer surface of a magnetic tape with a servo pattern formed thereon was used. Rough measurements were performed at a pitch of 100 nm in the measurement range of , and servo patterns (magnetized regions) were extracted. The distance between the magnetic layer surface and the probe tip during magnetic force microscopy was 20 nm. Since the measurement range includes five servo patterns of A burst formed according to the LTO Ultrium format, these five servo patterns were extracted.
Using the above-mentioned magnetic force microscope and probe, the vicinity of the boundary between the magnetized region and the non-magnetized region was measured at a pitch of 5 nm on the downstream edge of each servo pattern in the running direction to obtain a magnetic profile. Since the obtained magnetic profile was tilted at an angle α=12°, rotational correction was performed using analysis software so that the angle α=0°.
The measurements were performed at three different locations on the surface of the magnetic layer. Each measurement range included five A-burst servo patterns.
Thereafter, the difference (L _99.9 -L _0.1 ) was determined by the method described above using analysis software. As analysis software, MATLAB manufactured by MathWorks was used. The difference (L _99.9 −L _0.1 ) thus determined is shown in Table 1.

[Performance evaluation]
(1) The magnetic layer of each magnetic tape of Examples and Comparative Examples was recorded using a recording/reproducing head mounted on an IBM TS1155 tape drive at a speed of 6 m/s and a linear recording density of 600 kbpi (255 bit PRBS). ) and track pitch: 2 μm recording conditions. The above unit kbpi is a unit of linear recording density (cannot be converted into SI unit system). The above PRBS is an abbreviation for Pseudo Random Bit Sequence.
With the above recording, a specific track area in which the track to be read is located between two adjacent tracks, that is, between the first noise source track and the second noise source track, is created in the magnetic layer of each magnetic tape. It is formed.
(2) As a model experiment in which data is read using a reading element unit having two reading elements arranged in close proximity, the following data reading was performed. In the following model experiment, data was read by sliding the surface of the magnetic layer and the reading element in contact with each other.
Reading is started with a magnetic head having a single reading element arranged so that the center of the track to be read in the tape width direction matches the center of the reading element in the track width direction, and the first data reading is performed. went. During this first data reading, the servo pattern was read by the servo element, and timing-based servo tracking was also performed. Further, a data reading operation was performed by the reading element in synchronization with the servo pattern reading operation.
Next, the same magnetic head was shifted by 500 nm in the tape width direction (toward one adjacent track), and a second data reading was performed in the same manner as the first data reading. The above two data readings were performed under the following conditions: read element width: 0.2 μm, speed: 4 m/s, sampling rate: 1.25 times the bit rate.
The read signal obtained in the first data read was input to an equalizer, and waveform equalization processing was performed according to the amount of positional deviation between the magnetic tape and the magnetic head (reading element) in the first data read. . This waveform equalization process is performed as follows. The ratio of the overlapping area between the reading element and the track to be read and the overlapping area between the reading element and the adjacent track is calculated from the amount of positional deviation obtained by reading the servo pattern formed at a constant period with the servo element. Identify. Waveform equalization processing is performed by convolving the read signal with a tap coefficient derived from the specified ratio using an arithmetic expression. The above calculation formula is a calculation formula using EPR4 (Extended Partial Response class 4) as a basic waveform (target). The read signal obtained in the second data reading was similarly subjected to waveform equalization processing.
By performing phase matching processing (two-dimensional signal processing) of the two read signals that have been subjected to the waveform equalization processing described above, a readout having two reading elements arranged in close proximity (reading element pitch = 500 nm) is achieved. A read signal that would be obtained by the element unit was obtained. For the read signal thus obtained, the SNR at the signal detection point was calculated.
(3) Regarding (2) above, the position of the reading element at the start of the first data reading is set at 0.1 μm intervals from the center of the track to be read in the tape width direction on the first noise source track side and on the second noise source track side. This was repeated while the tracks were offset to the noise source track side, respectively, to obtain the envelope of the SNR with respect to the track position.
For each of the Example and Comparative Example, the SNR envelope was also obtained for only the first data reading result (that is, the data reading result with only a single element).
(4) The SNR envelope obtained for the data read results with only a single element was used as a reference envelope, and the point where the SNR decreased by -3 dB from the SNR of the track center in the reference envelope was set as the SNR lower limit value. In each envelope, the maximum track offset amount that was equal to or greater than this lower limit was defined as the allowable track offset amount. For each of the examples and comparative examples, the rate of increase in the allowable track offset amount relative to the allowable track offset amount for only a single element was determined as the "permissible track offset amount increase rate."

The above results are shown in Table 1 (Table 1-1 to Table 1-3).

As shown in Table 1, according to the example, it was possible to achieve an allowable track offset amount increase rate of 20% or more.
A large allowable track offset amount determined by the above method is advantageous in enabling reproduction with good reproduction quality even with a small track margin. From this point of view, it is preferable that the allowable track offset amount increase rate is 20% or more.
Note that the squareness ratio is generally known as an index of the state of existence of ferromagnetic powder in the magnetic layer. However, as shown in Table 1, even if the magnetic tapes have the same vertical squareness ratio, ΔN is different (for example, Examples 3 and 4, and Comparative Example 4). This is considered to indicate that ΔN is a value that is influenced by other factors in addition to the state of the ferromagnetic powder in the magnetic layer.

One embodiment of the present invention is useful in magnetic recording applications where it is desired to reproduce data recorded at high density with good reproduction quality.

Claims (13)

A magnetic tape comprising a non-magnetic support and a magnetic layer containing ferromagnetic powder,
A non-magnetic layer containing non-magnetic powder is provided between the non-magnetic support and the magnetic layer,
The vertical squareness ratio of the magnetic tape is 0.60 or more and 1.00 or less,
the magnetic layer has a timing-based servo pattern;
The edge shape specified by magnetic force microscopy observation of the timing-based servo pattern is determined by the cumulative distribution function L _99.9 of 99.9% of the positional deviation width from the ideal shape in the longitudinal direction of the magnetic tape and the cumulative distribution function. The shape has a shape in which the difference from the value L _0.1 of 0.1%, L _99.9 −L _0.1 , is 180 nm or less, and the refractive index Nxy measured in the in-plane direction of the magnetic layer and the above A magnetic tape, wherein the absolute value ΔN of the difference between the magnetic layer and the refractive index Nz measured in the thickness direction is 0.25 or more and 0.40 or less. The magnetic tape according to claim 1, wherein a difference between the refractive index Nxy and the refractive index Nz, Nxy-Nz, is 0.25 or more and 0.40 or less. The timing base servo pattern is a linear servo pattern that extends continuously from one side to the other in the width direction of the magnetic tape and is inclined at an angle α with respect to the width direction, and the ideal shape is The magnetic tape according to claim 1 or 2, which has a linear shape extending in the direction of an angle α. The magnetic tape according to any one of claims 1 to 3, wherein the difference, L _99.9 −L _0.1 , is 100 nm or more and 180 nm or less. The magnetic tape according to claim 1, wherein the magnetic layer has a thickness of 10 to 100 nm. The magnetic tape according to claim 1, wherein the magnetic layer has a thickness of 10 to 90 nm. The magnetic tape according to claim 1, wherein the magnetic layer has a thickness of 10 to 70 nm. The magnetic tape according to claim 1, wherein the magnetic layer has a thickness of 10 to 50 nm. The magnetic tape according to any one of claims 1 to 8, wherein the nonmagnetic layer has a thickness of 0.1 to 0.7 μm. The magnetic tape according to any one of claims 1 to 9, wherein the ferromagnetic powder has an average particle size of 25 nm or less. The magnetic tape according to any one of claims 1 to 10, further comprising a back coat layer containing nonmagnetic powder on a surface side of the nonmagnetic support opposite to the surface side having the magnetic layer. A magnetic tape cartridge comprising the magnetic tape according to any one of claims 1 to 11. magnetic tape and
a reading element unit;
an extraction section;
including;
The magnetic tape is the magnetic tape according to any one of claims 1 to 11,
The reading element unit is
comprising a plurality of reading elements each reading data from a specific track area including a track to be read among track areas included in the magnetic tape;
In the magnetic tape device, the extraction unit extracts data originating from the read target track from the read results by performing waveform equalization processing on each of the read results for each of the read elements.