JP2003257001A - Magnetic recording medium, information recorder and signal measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of recording a control signal with a very high degree of accuracy and obtaining timing information with a high degree of accuracy. <P>SOLUTION: A disk magnetic recording medium having at least a magnetic layer is constituted in such a manner that a signal is pre-recorded by the combination of a first magnetized state area with a second magnetized state area on the magnetic layer, the sum of the peripheral direction lengths of the first and second magnetized state areas is increased from an inner periphery to an outer periphery roughly in proportion to a radial position, and the ratio of the peripheral direction length of the first magnetized state to the peripheral direction length of the second magnetized state area is uniformly changed in accordance with the radial direction. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk-shaped magnetic recording medium such as a magnetic disk used for a magnetic recording device, a signal measuring device and an information recording device which can be used for the same.

[0002]

2. Description of the Related Art A magnetic recording device represented by a hard disk drive is widely used as an external storage device of an information processing device such as a computer, and in recent years, it has also been used as a recording device for a moving image or a recording device for a set top box. It's starting. A magnetic recording device usually has one or more magnetic disks (hard disks) and a recording / reproducing head built-in. The recording / reproducing head is usually a flying head, and is provided so as to move on the magnetic disk with a constant flying height. In addition to the flying head, use of a contact head (contact head) has also been proposed in order to further reduce the distance to the medium.

A magnetic recording medium such as a magnetic disk is generally formed by sequentially laminating a NiP layer, a metal underlayer, a magnetic layer (recording layer), a protective layer and a lubricating layer on the surface of an aluminum alloy substrate or the like. Alternatively, a metal underlayer, a magnetic layer (recording layer), a protective layer, a lubricating layer and the like are sequentially laminated on the surface of a glass substrate or the like. The magnetic recording medium includes an in-plane magnetic recording medium and a perpendicular magnetic recording medium. Longitudinal recording is usually performed on the longitudinal magnetic recording medium.

A disk-shaped magnetic recording medium typified by a magnetic disk is usually provided with recording tracks concentrically,
A control signal for performing position control (positioning) and synchronization control of the recording / reproducing magnetic head is recorded in advance for each recording track. For example, it is a control signal such as a servo signal for positioning the magnetic head. Conventionally, this control signal is recorded by alternately providing regions of the first magnetization state and regions of the second magnetization state at specific positions on the medium. Normal,
The first magnetization state and the second magnetization state are opposite to each other in the direction of magnetization. In the case of an in-plane magnetic recording medium, one direction in the longitudinal direction and its opposite direction, and in the case of a perpendicular magnetic recording medium, the medium is It corresponds to one direction in the vertical direction and the opposite direction.

These are generally recorded by using a magnetic head. Scan the magnetic head while rotating the medium,
The magnetization state is recorded by passing a current through the head, but the recording of the first magnetization state and the recording of the second magnetization state are switched by reversing the direction of the flowing current each time. The part where the direction of the current is reversed corresponds to the magnetization reversal part of the medium. In this recording method, usually, the respective magnetization reversals are recorded with the same accuracy. That is, the region widths of the first magnetization state and the second magnetization state are usually formed to be almost equal. One reason is that the structure of the head is generally symmetric with respect to the direction of current flow.

[0006]

By the way, since the control signals such as servo signals usually need to generate the same frequency on the inner and outer circumferences of the disk-shaped magnetic recording medium, the regions of the first and second magnetization states are generated. It was necessary to make the width narrow at the inner circumference and wide at the outer circumference. In recent years, a magnetic transfer system has come to be used for recording these signals. In this technique, the magnetic recording medium, which has been magnetized to a second magnetization state (first magnetization direction) almost uniformly in advance, inverts only a specific region defined by a master mold such as a mask or a master disk. This is a technique for recording a signal by performing an operation to form a magnetized region having a first magnetized state (second magnetized direction) at a specific position.

The magnetic transfer method has an advantage that various fine magnetization patterns can be formed accurately and collectively in a batch. However, unlike the recording method using the magnetic head, the region widths of the first magnetization state and the second magnetization state tend to be different. If the two region widths are different, the timing asymmetry value is deteriorated, and there is a possibility that a highly accurate signal cannot be obtained.

Further, in the magnetic transfer system, the most accurate transfer condition differs depending on the width of the magnetized area. Therefore, as described above, at the same frequency on the inner and outer circumferences, the first,
When a signal is formed in which the region width of the second magnetization state is greatly different between the inner and outer circumferences, there is a problem in that it is difficult to obtain a highly accurate signal over the entire surface. Therefore, there has been a demand for a magnetic recording medium that can obtain a highly accurate control signal over the entire surface, regardless of the recording method.

It is an object of the present invention to provide a magnetic recording medium from which a control signal can be obtained with extremely high accuracy, and a signal measuring device and an information recording device which can be preferably applied to the magnetic recording medium.

[0010]

SUMMARY OF THE INVENTION The gist of the present invention is a disk-shaped magnetic recording medium having at least a magnetic layer,
A signal in which a region of the first magnetization state and a region of the second magnetization state are recorded in advance on the magnetic layer, and the circumferential direction of the regions of the first and second magnetization states which are adjacent to each other. The sum of the lengths increases from the inner circumference to the outer circumference approximately in proportion to the radial position, and the circumferential length of the region in the first magnetization state and the circumferential direction of the region in the second magnetization state. The present invention resides in a magnetic recording medium characterized in that the length ratio changes uniformly according to the radial position. Another aspect of the present invention is to provide a recording medium having a plurality of recording tracks on which servo signals are recorded, a drive unit for driving the recording medium in the recording direction, and a recording / reproducing head movable in the transverse direction of the recording tracks. And wherein the servo signal has alternating positive and negative pulses, a first time interval from the positive pulse to the negative pulse, and
The second time interval from the negative pulse to the positive pulse is different, and the ratio of the first time interval to the second time interval varies uniformly across the recording track. , Of the zero-cross points associated with the transition from the positive pulse to the negative pulse and the zero-cross points associated with the transition from the negative pulse to the positive pulse, whichever one has a greater slope and crosses the zero point. An information recording apparatus is characterized in that the timing at a zero-cross point is measured, and the position of a recording / reproducing head is controlled based on the result of the measurement to perform recording / reproducing. Yet another gist of the present invention is that positive and negative pulses alternate.
A device for measuring the timing of a signal having a different first time interval from the positive pulse to the negative pulse and a second time interval from the negative pulse to the positive pulse, the device comprising: Of the zero-cross points associated with the transition from the pulse to the negative pulse and the zero-cross points associated with the transition from the negative pulse to the positive pulse, at the zero-cross point where the signal crosses the zero point with a large slope. The signal measuring apparatus is characterized by measuring timing.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION That is, according to the present invention, in a disk-shaped magnetic recording medium, a signal due to a combination of a region having a first magnetization state and a region having a second magnetization state is previously recorded in a magnetic layer, The sum of the circumferential lengths of the regions of the first and second magnetized states, which are adjacent to each other, is from the inner circumference to the outer circumference,
By increasing in proportion to the radial position, the signal having the same frequency is obtained at any radial position. Then, the ratio of the circumferential length of the first magnetized state region to the circumferential length of the second magnetized state region changes uniformly according to the radial position. In the present invention, the uniform change means a uniform increase or a uniform decrease. A uniform increase means an increase without a decrease, and a uniform decrease means a decrease without an increase. The change may be uniform, may be changed linearly, may be changed curvilinearly such as a quadratic function, and may be changed stepwise. It preferably changes continuously and linearly in the radial direction. That is, it increases continuously and linearly in the radial direction, or decreases continuously and linearly in the radial direction. Particularly preferably, the circumferential length of the first magnetized state region is substantially constant regardless of the radial position. In the present invention, “generally constant” does not have to be exactly constant, and for example, a fluctuation of about ± 10% is allowed. Similarly, being roughly proportional to the radial position does not have to be exactly proportional to the radial position, and allows a fluctuation of, for example, about ± 10%. That is, in the disk-shaped magnetic recording medium,
By maintaining the sum of the area width of the adjacent first magnetization state and the area width of the second magnetization state to a value approximately proportional to the radial position, with a signal of the same frequency at any radial position, It is characterized in that the circumferential length of the first magnetized state, that is, the region width of the first magnetized state in the recording track direction is made substantially constant regardless of the radius.

In the conventional signal in which the first magnetized state region and the second magnetized state region are arranged at equal intervals, the peak positions of the positive and negative signals in the signal waveform reproduced from the magnetization reversal portion between the two regions. Was used to control the position of the magnetic head. On the other hand, in the present invention, the peak position itself of the positive and negative signals differs depending on the radial position. However, highly accurate control is possible by using the center positions of adjacent positive and negative signals.

That is, a positive pulse is detected at the transition point from the second magnetization state to the first magnetization state, and a negative pulse is detected at the transition point from the first magnetization state to the second magnetization state. Then, the center position of both pulses indicates the center point of the first magnetization state region. The center point of the first magnetization state region is the center position of the signal pattern provided on the master block used for transfer. Even if the width of the transferred pattern changes due to changes in the transfer conditions, the center position does not change and transfer is performed with high accuracy. Therefore, if the center point of the first magnetization state region is used, a control signal with high accuracy can be obtained. Is obtained.

The center position can be determined by measuring the position of each pulse and arithmetically averaging the positions. Also, if the pattern is designed so that positive and negative pulses are generated relatively close to each other, the center position of both pulses has a large slope and the signal crosses the zero point,
The position can be determined relatively easily by the processing using the electronic circuit. In this way, when position measurement is performed by detecting a point where the signal crosses the zero point with a large slope,
Positioning can be performed with higher accuracy than before. That is, in the present invention, positive and negative pulses appear alternately, and the first time interval from the positive pulse to the negative pulse and the second time interval from the negative pulse to the positive pulse are different. Is a device for measuring the timing of various signals, and a signal with a large slope is selected from the zero-cross point associated with the transition from a positive pulse to a negative pulse and the zero-cross point associated with the transition from a negative pulse to a positive pulse. Is characterized by a signal measuring device that measures the timing at the zero-cross point that crosses the zero point. According to this, since the so-called center position of the pulse can be determined with high accuracy, a more accurate timing signal can be obtained, and positioning can be performed with higher accuracy than in the past. It is also possible to provide an information recording device to which such a signal measuring device is applied. That is, an information recording apparatus including a recording medium having a plurality of recording tracks on which servo signals are recorded, a drive unit for driving the recording medium in the recording direction, and a recording / reproducing head movable in the transverse direction of the recording tracks. This is combined with this signal measuring device. The servo signal recorded on the medium has alternating positive and negative pulses, a first time interval from the positive pulse to the negative pulse, and a second time interval from the negative pulse to the positive pulse. And the ratio of the first time interval to the second time interval varies uniformly in the transverse direction of the recording track.
Then, of the zero-cross points accompanying the transition from the positive pulse to the negative pulse and the zero-cross points accompanying the transition from the negative pulse to the positive pulse, at the zero-cross point where the signal crosses the zero point with a large slope. The timing is measured, and the position of the recording / reproducing head is controlled based on the measurement result to perform recording / reproduction. According to this, the density of the recording tracks can be increased, and more accurate positioning can be performed in the recording tracks, so that it is possible to provide an information recording apparatus capable of recording and reproducing information at a higher density. Preferably, the medium is a magnetic recording medium such as a hard disk, and the information recording device is a hard disk drive.

The present invention will be described in detail with reference to the drawings. Figure 1
FIG. 3 is a schematic view showing an example of a magnetic recording medium of the present invention.
A large number of servo signal recording sections 2 are formed on a disk-shaped magnetic recording medium 1.
The (spokes) are provided radially in a curved shape. In the servo signal recording unit 2, various control signals such as servo signals and synchronization signals (clock signals, timing signals) are collected and recorded.

FIG. 2 is an enlarged view of the servo signal recording section 2 of FIG. 1, and schematically shows a clock signal provided therein. The circumferential length of the first magnetized state region 3 is constant at all radial positions, whereas the circumferential length of the second magnetized state region 4 is indicated by the inner peripheral portion (A in the figure). ) Is narrow, and the outer circumference (indicated by B in the figure) is wide.

Moreover, since the total value of the circumferential lengths of the first magnetized state region 3 and the second magnetized state region 4 adjacent to each other is set to be a value proportional to the radial position, The frequency of the clock signal reproduced from the disk-shaped magnetic recording medium rotating at a constant speed has a constant value regardless of the radius. FIG. 3 is a schematic diagram showing a signal waveform reproduced from the clock signal shown in FIG. The signal waveform reproduced at the inner peripheral portion A is shown by a solid line, and the signal waveform reproduced at the outer peripheral portion B is shown by a dotted line. The zero cross point indicated by the arrow indicates the center position of the first magnetization state region 3 shown in FIG. As can be seen from the figure, the zero cross points are the same at the inner peripheral portion and the outer peripheral portion, and it can be seen that the zero cross points do not change depending on the radial position. This point is used as a signal for control. This point can be detected very easily by a simple electronic circuit by detecting the point where zero is crossed after the output signal exceeds a certain positive value.
And it can be detected with high accuracy.

The present invention is suitable for forming a control signal for controlling the recording / reproducing magnetic head. For example, it is a pattern for generating a signal corresponding to the position of the head. The control signal controls recording / reproducing means such as a magnetic head using the signal. For example, the control signal indicates a servo signal for positioning the magnetic head on a data track, or the position of the magnetic head on the medium. An address signal, a sync signal for controlling the recording / reproducing speed by the magnetic head, and the like are included. Alternatively, a reference signal for later writing the servo signal is also included.

Such a signal can be easily formed by a so-called magnetic transfer system in which a signal pattern provided on a mother die is transferred to the magnetic recording medium. In particular, after applying a first external magnetic field to the magnetic recording medium to uniformly magnetize the magnetic layer to a first magnetization state, the magnetic layer is passed through a mask provided with a transmissive portion and a non-transmissive portion for energy rays. Of the magnetic layer to locally heat the irradiated portion of the magnetic layer and at the same time to apply a second external magnetic field to magnetize the heated portion in the direction opposite to the desired direction and thereby the second magnetized state region. It is possible to easily record by forming the.

This signal recording method (magnetization pattern forming method)
Will be described in more detail. In the present magnetization pattern forming method, a first external magnetic field is applied to uniformly magnetize the magnetic layer in advance to a first magnetization state (a state having a desired magnetization direction), and then the magnetic layer is locally heated at the same time. A second external magnetic field is applied to magnetize the heating portion in a direction opposite to the desired direction (second magnetization state) to form a magnetization pattern. As a result, magnetic domains in opposite directions are clearly formed, so that a magnetic pattern having a high signal strength and a good C / N and S / N can be obtained.

First, a strong first external magnetic field is applied to the magnetic recording medium to uniformly magnetize the entire magnetic layer in a desired magnetization direction. A magnetic head may be used as the means for applying the first external magnetic field, or an electromagnet or a permanent magnet may be arranged so as to generate a magnetic field in a desired magnetization direction. Further, these means may be used in combination. In the case of a medium having an easy axis of magnetization in the in-plane direction, the desired magnetization direction is the same as or opposite to the running direction of the data recording / reproducing head (the relative movement direction of the medium and the head), When the easy axis of magnetization is perpendicular to the in-plane direction, it is either in the vertical direction (upward or downward). Therefore, the first external magnetic field is applied so as to be magnetized as such. When the medium has a disk shape, the application direction of the first external magnetic field is preferably the circumferential direction, the radial direction, or the direction perpendicular to the plate surface.

Further, to uniformly magnetize the entire magnetic layer in a desired direction means to magnetize all of the magnetic layer in substantially the same direction, but not strictly all, and at least a region where a magnetization pattern is to be formed. It only has to be magnetized in the same direction. The strength of the first external magnetic field may be set according to the coercive force of the magnetic layer, but it is preferable to magnetize the magnetic layer with a magnetic field that is at least twice the coercive force (static coercive force) of the magnetic layer at room temperature. If it is weaker than this, the magnetization may be insufficient.
However, it is usually about 5 times or less the coercive force of the magnetic layer at room temperature due to the capability of the magnetizing device used for applying the magnetic field. Room temperature is, for example, 25 ° C. The coercive force of the magnetic recording medium is almost the same as the coercive force of the magnetic layer (recording layer).

The magnetic layer generally has a static coercive force (sometimes simply referred to as a coercive force) and a dynamic coercive force. For local heating, at least up to a temperature at which the dynamic coercive force of the magnetic layer decreases to some extent. It only needs to be heated. Of course, you may heat to the temperature which static coercive force falls. Preferably 10
Heat to above 0 ° C. A magnetic layer that is affected by an external magnetic field at a heating temperature of less than 100 ° C. tends to have low magnetic domain stability at room temperature.

However, it is desirable that the heating temperature is as low as possible in a range where a desired decrease in coercive force can be obtained. For example, up to near the magnetization disappearance temperature or the Curie temperature of the magnetic layer. If the heating temperature is too high, heat diffusion easily occurs in areas other than the area to be heated, and the pattern may be blurred. In addition, the magnetic layer may be deformed. Furthermore, a lubricating layer made of a lubricant is usually formed on the surface of the magnetic recording medium, and the lower heating temperature is more preferable in order to prevent adverse effects such as deterioration of the lubricant due to heating. The heating may cause deterioration such as decomposition of the lubricant, or may be vaporized and reduced, and particularly in the case of proximity exposure, the vaporized lubricant may adhere to a mask or the like. Therefore, it is desirable that the heating temperature is as low as possible in order to industrially apply the present magnetization pattern forming method to a magnetic recording medium provided with a lubricating layer.

Therefore, it is preferable that the heating temperature is not higher than the Curie temperature of the magnetic layer. For example, the temperature is preferably 300 ° C or lower, more preferably 250 ° C or lower, and further preferably 200 ° C or lower. Then, the direction of the second external magnetic field applied simultaneously with the heating is generally opposite to the direction of the first external magnetic field. When the medium has a disk shape, it is preferable that the second external magnetic field is applied in the circumferential direction, the radial direction, or the direction perpendicular to the plate surface.

When the pulsed energy beam is used for heating, the second external magnetic field may be applied continuously or in a pulsed manner. When the second external magnetic field is a pulsed magnetic field, it may be only the pulsed magnetic field component or a combination of the pulsed magnetic field component and the static magnetic field component. At this time, the sum of the pulsed magnetic field component and the static magnetic field component is the strength of the second external magnetic field.

The higher the maximum intensity of the second external magnetic field, the easier the formation of the magnetization pattern. The optimum strength varies depending on the characteristics of the magnetic layer of the magnetic recording medium, but when the second external magnetic field is a static magnetic field, it is preferably 1/8 or more of the coercive force (static coercive force) at room temperature. If it is weaker than this, the heating part may be magnetized again in the same direction as the surroundings under the influence of the magnetic field from the surrounding magnetic domains during cooling. However, the coercive force of the magnetic layer at room temperature is preferably 2/3 or less.
It is more preferable to set it to / 2 times or less. If it is larger than this, the magnetic domains around the heating portion may be affected.

When the second external magnetic field is a pulsed magnetic field, it is preferably 2/3 or more of the coercive force (static coercive force) at room temperature. If it is too weak, the heated region may not be magnetized well. More preferably, it is 3/4 or more of the static coercive force at room temperature. A magnetic field stronger than the static coercive force at room temperature may be applied. However, the magnetic field is smaller than the dynamic coercive force of the magnetic layer at room temperature. This is because if the second external magnetic field is larger than this, it will affect the magnetization of the non-heated region.

In this method, the magnetic field strength value H (O
The value e) can be directly substituted by the value B (Gauss) of the magnetic flux density. Generally, there is a relationship of B = μH (where μ represents magnetic permeability), but since the magnetization pattern is usually formed in air, the magnetic permeability is 1, and the relationship of B = H is established. is there. As the means for applying the second external magnetic field, a magnetic head may be used, or a plurality of electromagnets or permanent magnets may be arranged and used so that a magnetic field is generated in a desired magnetization direction. You may use it in combination. Permanent magnets such as ferrite magnets, neodymium-based rare earth magnets, and samarium-cobalt-based rare earth magnets are suitable for efficiently magnetizing a high-coercivity medium suitable for high-density recording.

When the second external magnetic field is a pulsed magnetic field, only the pulsed magnetic field applying means may be used, or a combination of the pulsed magnetic field applying means and the static magnetic field applying means may be used. For example, in the former case, only a pulsed magnetic field is generated by an electromagnet or the like. For example, in the latter case, a static magnetic field of a certain magnitude is given by a permanent magnet or an electromagnet, and a magnetic field higher than that is applied in a pulse form by the electromagnet. It is preferable to use an air-core coil having a small inductance because the pulse width can be narrowed and the magnetic field application time can be shortened. Also, instead of the permanent magnet, another yoke-type electromagnet or the like may be used.

When the static magnetic field and the pulsed magnetic field are combined,
The magnetic field applied in pulses can be reduced. Generally, it becomes more difficult for the electromagnet to shorten the pulse width as the magnetic field increases, so that the pulse width is likely to be shortened accordingly. Alternatively, the pulsed magnetic field can be applied by a method in which a magnet that constantly generates a magnetic field is brought close to the magnetic recording medium for a short time. For example, the medium may be rotated at a speed higher than a predetermined speed while applying a magnetic field to a part of the magnetic recording medium with a permanent magnet. When the second external magnetic field is a combination of a static magnetic field and a pulsed magnetic field, the magnetic field strength of the static magnetic field is made smaller than the static coercive force of the magnetic layer at room temperature. It is preferably 2/3 or less of the static coercive force, and more preferably 1/2.
Double or less. If it is too large, it affects the formed magnetization pattern, which not only reduces the output but also deteriorates the modulation. There is no particular lower limit, but if it is too weak, the meaning of using a static magnetic field becomes small. Therefore, for example, it is set to 1/8 or more of the static coercive force of the magnetic layer at room temperature. Then the second
The pulse width when the external magnetic field is a pulsed magnetic field will be described. In this method, the pulse width of the pulsed magnetic field component of the second external magnetic field is simply referred to as the pulse width of the second external magnetic field.
Here, the pulse width of the magnetic field refers to the half width.

The pulse width of the second external magnetic field is usually 100 ms.
ec or less. It is preferably 10 msec or less.
The shorter the pulse width of the second external magnetic field, the larger the upper limit of the magnetic field that can be applied. This is because the value of the dynamic coercive force changes depending on the application time of the magnetic field, and the shorter the pulse width of the second external magnetic field, the greater the dynamic coercive force of the magnetic layer at room temperature. It is more preferably 1 msec or less. However, it is preferably 10 nsec or more. If it is too short, the dynamic coercive force will increase, and the second external magnetic field required to magnetize the heating region will increase. Further, although it depends on the magnitude of the magnetic field, it takes time for the magnetic field to rise and fall due to the characteristics of the electromagnet, so there is a limit to shortening the pulse width. More preferably, it is 100 nsec or more. Here, the pulse width of the magnetic field refers to the full width at half maximum.

When a pulsed energy ray is used for local heating, the pulse width of the second external magnetic field is set to be larger than the pulse width of the pulsed energy ray. This is because if it is less than this value, the magnetic field will change during local heating, and the magnetization pattern will not be formed well. Further, it is preferable that the pulsed energy ray and the pulsed second external magnetic field are synchronized and applied simultaneously. Normally, the pulse width of the magnetic field is considered to be longer than the pulse width of the energy beam, but in this case, the second
It is preferable to apply a pulse of an external magnetic field and control so that the pulse of the energy ray is applied where the magnetic field becomes maximum.

A magnetic recording medium or AFC with enhanced dynamic coercive force
Applying a pulsed magnetic field as the second external magnetic field to the medium is particularly effective. For example, a magnetic recording medium having two magnetic layers, which has a magnetic layer for recording and a stabilizing magnetic layer for maintaining thermal stability, may be mentioned. Since the stabilizing magnetic layer acts to suppress the instantaneous magnetization reversal of the recording magnetic layer, the dynamic coercive force is high and it is difficult to form a magnetization pattern by the conventional method. An excellent magnetic pattern can be formed by applying an external magnetic field in the vicinity of a static coercive force or higher to such a medium in pulses.

The second external magnetic field can also form a plurality of magnetization patterns at once by applying the external magnetic field over the heated wide area. When local heating can be performed on the entire surface of the magnetic recording medium at one time, it is desirable to apply a second external magnetic field to the entire surface of the medium at the same time as heating to form a magnetization pattern. Thereby, the magnetization pattern can be formed in a shorter time, and the cost can be greatly reduced. Further, in order to apply the magnetic field to only a part of the medium, it is often the case that the magnet arrangement is devised or specific measures are taken so that the magnetic field does not reach the other areas, but it is necessary to apply it to the entire surface. Absent. Moreover, since the rotating mechanism or the moving mechanism is not necessary, the device configuration is simple and the magnetic recording medium can be obtained at a low cost.

For example, when the medium is a small disk-shaped magnetic recording medium having a diameter of 2.5 inches or less, it is preferable that energy rays can be irradiated and a magnetic field can be applied to the entire surface of the disk by a simple arrangement or means. More preferably, the diameter is 1 inch or less. Further, when it is desired to apply a magnetic field to the disk-shaped magnetic recording medium in the circumferential direction, a large vertical pulse current can be passed through the center of the medium to easily generate a magnetic field in the circumferential direction. This is especially the diameter 1
It is preferably applied to a disk-shaped magnetic recording medium having a small diameter of not more than inch.

In the local heating means of the magnetic layer in the present method, an energy ray such as a laser, which is easy to control the power and the size of the heated portion, is used in consideration of prevention of thermal diffusion to an unnecessary portion and controllability. To use. When the mask is used together, a plurality of magnetization patterns can be formed at one time by irradiating the energy rays through the mask, so that the magnetization pattern forming step is short and simple.

It is preferable that the energy beam is pulsed rather than continuous irradiation to control the heating site and control the heating temperature. The use of a pulsed laser light source is particularly preferable. A pulsed laser light source oscillates a laser in a pulsed manner intermittently, and compared with a continuous laser that is intermittently pulsed by an optical component such as an acousto-optic device (AO) or an electro-optic device (EO), It is possible to irradiate a laser having a high power peak value in a very short time, and it is very preferable that heat is hardly accumulated.

It is preferable that the medium surface on which the magnetization pattern is formed has a large temperature difference between the irradiation of the pulsed energy beam and the non-irradiation of the medium in order to increase the contrast of the pattern or increase the recording density. Therefore, it is preferable that the temperature is about room temperature or lower when the pulsed energy beam is not irradiated. Room temperature is about 25 ° C. When using the pulsed energy beam, the external magnetic field may be continuously applied or pulsed.

The wavelength of the energy rays is preferably 1100 nm or less. If the wavelength is shorter than this, the diffraction effect is small and the resolution is increased, so that it is easy to form a fine magnetization pattern. More preferably, the wavelength is 600 nm or less. Not only the resolution is high, but also the diffraction is small, so that the spacing between the mask and the magnetic recording medium can be widely taken due to the gap, and the handling is easy, and the magnetization pattern forming device can be easily configured. The wavelength is 1
It is preferably 50 nm or more. If it is less than 150 nm, the absorption of synthetic quartz used for the mask becomes large, and heating tends to be insufficient. If the wavelength is 350 nm or more, the optical glass can be used as a mask.

Specifically, the excimer laser (157, 1
93, 248, 308, 351 nm), a YAG Q-switched laser (1064 nm) second harmonic (532 nm),
3rd harmonic (355nm) or 4th harmonic (266nm),
Examples thereof include Ar laser (488 nm, 514 nm) and ruby laser (694 nm). The power of energy rays is
The optimum value may be selected depending on the magnitude of the external magnetic field, but the power per pulse of the pulsed energy beam is 100.
It is preferably 0 mJ / cm ² or less. If a power larger than this is applied, the surface of the magnetic recording medium may be damaged and deformed by the pulsed energy rays. If the roughness Ra of the medium increases to 3 nm or more and the waviness Wa increases to 5 nm or more due to the deformation, the running of the flying / contact type head may be hindered. More preferably 5
00 mJ / cm ² or less, more preferably 200 m
J / cm ² or less. In this region, it is easy to form a magnetization pattern with high resolution even when a substrate having a relatively large thermal diffusion is used. The power is preferably 10 mJ / cm ² or more. If it is smaller than this, the temperature of the magnetic layer is hard to rise and magnetic transfer is hard to occur. In addition, since the influence of the diffraction of the energy beam changes depending on the pattern width, the optimum power also changes according to the pattern width. Also, the shorter the wavelength of the energy rays, the lower the upper limit of the power that can be applied tends to decrease. Also, if there is concern about damage to the magnetic layer, protective layer, or lubricating layer due to energy rays, reduce the power of pulsed energy rays,
It is also possible to take measures to increase the strength of the magnetic field applied at the same time as the pulsed energy rays. For example, the irradiation energy is lowered by applying a magnetic field as large as possible within the range of 25 to 75% of the coercive force of the magnetic recording medium at room temperature.

When irradiating the pulsed energy beam through the protective layer and the lubricating layer, it may be necessary to re-apply after irradiation in consideration of damage (decomposition, polymerization) to the lubricant. . The pulse width of the pulsed energy beam is preferably 1 μsec or less. If the pulse width is wider than this, the heat generated by the energy applied to the magnetic recording medium is dispersed, and the resolution is likely to decrease. When the power per pulse is the same, when the pulse width is shortened and strong energy is applied at one time, thermal diffusion tends to be small and the resolution of the magnetization pattern tends to be high. More preferably 1
It is 00 nsec or less. In this region, it is easy to form a magnetization pattern with high resolution even when a substrate such as Al having a relatively large thermal diffusion is used. When forming a pattern having a minimum width of 2 μm or less, the pulse width is set to 25 nse.
It is preferably c or less. That is, if the resolution is important, the shorter the pulse width, the better. The pulse width is preferably 1 nsec or more. This is because it is preferable to keep heating for the time until the magnetization reversal of the magnetic layer is completed.

In the present application, the minimum width of the pattern means the narrowest length in the pattern. A square pattern has a short side, a circle has a diameter, and an ellipse has a short diameter. As a kind of pulsed laser, there is a laser capable of generating an ultrashort pulse of picosecond or femtosecond level at a high frequency like a mode-locked laser. During the period of irradiating the ultra-short pulse with a high frequency, the laser is not emitted for a very short time between the ultra-short pulses, but the heating portion is hardly cooled because it is a very short time. That is, the region once heated to the Curie temperature or higher is kept at the Curie temperature or higher. Therefore, in such a case, the continuous irradiation period (the continuous irradiation period including the time during which the laser is not irradiated during the ultrashort pulse) is set to one pulse. The integrated value of the irradiation energy amount during the continuous irradiation period is the power per pulse (mJ / cm ² ). The mask of the present invention is preferably a so-called photomask having an energy ray transmitting portion and an energy ray non-transmitting portion. The energy ray intensity distribution is changed in accordance with the magnetization pattern to be formed, and the energy ray concentration on the magnetic disk surface is changed. (Intensity distribution) is formed. This allows
Since a plurality of or large area magnetization patterns can be formed at one time, the magnetization pattern forming step becomes short and simple. Photomasks are preferable in that they can be produced easily and inexpensively.

The mask does not have to cover the entire surface of the magnetic disk. If there is a size including a repeating unit of the magnetization pattern, it can be moved and used. The mask is arranged between the light source of energy rays and the magnetic recording medium. If importance is placed on the accuracy of the magnetization pattern, it is preferable to bring all or part of the mask into contact with the medium. The influence of laser light diffraction can be minimized, and a magnetization pattern with high resolution can be formed. For example, when the mask is allowed to stand on the medium, undulations of several .mu.m on the surface of the medium may cause a portion that contacts the medium and a portion that does not contact the medium. However, the pressure applied to the mask and the medium is 100 g / cm ² or less so that the medium is not indented or damaged.

However, in order to reduce defects and scratches,
It is preferable to provide a gap between the mask and the medium at least in the region where the magnetization pattern of the medium is formed. It is possible to suppress scratches on the medium and the mask due to entrapment of dust and the like and generation of defects. Further, when the lubricating layer is provided before the formation of the magnetization pattern, it is particularly preferable to provide a gap between the mask and the medium. This is to minimize the adhesion of lubricant to the mask. Also, when a mask with a disk provided with a lubricating layer is contacted with a high-power energy beam, a rapid vaporization of the lubricant causes an explosive state, causing the lubricant to scatter or even damage the mask. This is because there is a risk of As a method for maintaining the gap between the magnetic pattern forming region of the magnetic recording medium and the mask, it is possible to keep the both at a constant distance. For example, the mask and the medium may be held by a specific device to keep a certain distance. Further, a spacer may be inserted between the two in a place other than the magnetic pattern forming region. A spacer may be integrally formed on the mask itself.

The spacer is preferably made of a hard material. Further, since an external magnetic field is used for pattern formation, it is preferable that the pattern is not magnetized. Preferred are metals such as stainless steel and copper, and resins such as polyimide. The height is arbitrary, but is usually several μm to several hundreds μm. If a spacer is provided between the mask and the magnetic recording medium at the outer peripheral portion and / or the inner peripheral portion of the magnetic pattern forming region of the medium, the effect of correcting the waviness of the surface of the magnetic recording medium is created, and thus the accuracy of the magnetic pattern formation is improved. So good.

The material of the mask is not limited, but if the mask is made of a non-magnetic material in the present invention, a magnetized pattern can be formed with uniform clarity in any pattern shape, and a uniform and strong reproduction signal can be obtained. Photo mask
For example, a desired transparent portion and a non-transparent portion can be formed by forming a metal such as Cr by sputtering on a transparent master such as quartz glass or soda lime glass, applying a photoresist thereon, and etching. In this case, the portion having the Cr layer on the master is the energy ray non-transmissive portion, and the portion only on the master is the transparent portion.

The mask thus formed usually has unevenness, and the projections are opaque to the energy rays, and the projections are brought close to or in contact with the medium. Alternatively,
After forming such a mask, it is also possible to embed a material that is transparent to energy rays in the recesses and flatten the substantially contact surface with the medium for use.

[0049]

As described in detail above, the magnetic recording medium according to the present invention can record a control signal with extremely high accuracy, and can obtain timing information with high accuracy by a simple electronic circuit. It greatly contributes to higher recording density and cost reduction of magnetic recording devices such as hard disks. Further, by using the signal measuring device according to the present invention, the density of the recording tracks can be increased, and more accurate positioning can be performed in the recording tracks. Therefore, an information recording device capable of recording and reproducing information at a higher density can be provided. Can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a magnetic recording medium of the present invention.

FIG. 2 is a schematic diagram showing an example of a signal according to the present invention.

FIG. 3 is a schematic diagram showing a signal waveform reproduced from a magnetic recording medium according to the present invention.

[Explanation of symbols]

1 Magnetic recording medium 2 Servo signal recording section 3 First magnetization state region 4 Second magnetization state region

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 5/86 G11B 5/86 C 101 101B

Claims (8)

[Claims] 1. A disk-shaped magnetic recording medium having at least a magnetic layer, wherein a signal by a combination of a region of a first magnetization state and a region of a second magnetization state is previously recorded in the magnetic layer. The sum of the circumferential lengths of the regions of the first and second magnetized states that are adjacent to each other increases from the inner circumference to the outer circumference approximately in proportion to the radial position, and A magnetic recording medium, characterized in that a ratio of a circumferential length of a region in one magnetization state to a circumferential length of a region in the second magnetization state uniformly changes according to a radial position. 2. The magnetic recording medium according to claim 1, wherein the circumferential length of the region in the first magnetization state is substantially constant regardless of the radial position. 3. The signal is recorded by transferring a signal pattern provided on a matrix to the magnetic recording medium.
The magnetic recording medium according to claim 1. 4. A magnetic field is applied with a first external magnetic field to uniformly magnetize the magnetic layer to a first magnetization state, and then an energy ray transmitting portion and a non-transmitting portion are provided. Energy rays are radiated through the mask to locally heat the irradiated portion of the magnetic layer, and at the same time, a second external magnetic field is applied to magnetize the heated portion in a direction opposite to the desired direction to generate a second magnetization. The magnetic recording medium according to claim 1, wherein the signal is recorded by forming a state area. 5. The magnetic recording medium according to claim 1, wherein the signal is a control signal having information for controlling a recording / reproducing magnetic head. 6. The magnetic recording medium according to claim 5, wherein the control signal includes a servo signal for controlling the position of the recording / reproducing magnetic head or a reference signal for recording the servo signal. 7. A recording medium having a plurality of recording tracks on which servo signals are recorded, a drive unit for driving the recording medium in the recording direction, and a recording / reproducing head movable in the transverse direction of the recording tracks. The servo signal includes alternating positive and negative pulses, a first time interval from the positive pulse to the negative pulse, and a second time interval from the negative pulse to the positive pulse. The time interval is different, and the ratio of the first time interval to the second time interval varies uniformly in the transverse direction of the recording track, and the transition from the positive pulse to the negative pulse is made. Of the accompanying zero-cross points and the zero-cross points associated with the transition from the negative pulse to the positive pulse, the timing at the zero-cross point where the signal crosses the zero point with a large slope is measured, and the measurement result is also displayed. And the position of the recording / playback head An information recording device characterized by controlling and recording / reproducing. 8. Positive and negative pulses alternate, with a first time interval from the positive pulse to the negative pulse and a second time interval from the negative pulse to the positive pulse. Is a device for measuring the timing of different signals, and a larger one of the zero-cross points associated with the transition from the positive pulse to the negative pulse and the zero-cross points associated with the transition from the negative pulse to the positive pulse A signal measuring device characterized by measuring a timing at a zero cross point where a signal crosses a zero point with an inclination.