JPH0426914A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To satisfy both of high electromagnetic conversion characteristics and the durability at and under a high temp. and high humidity by lowering the Co content in the ferromagnetic metallic thin film of the lowermost layer than the Co content of the ferromagnetic metallic thin film of the uppermost layer. CONSTITUTION:This recording medium has a magnetic layer constituted of at least two layers of the ferromagnetic metallic thin films on a nonmagnetic substrate. The ferromagnetic metallic thin films consist essentially of Co and Ni or consist essentially of Co, Ni and Cr. The lowermost layer of these ferromagnetic metallic thin films, i.e. the ferromagnetic metallic thin film nearest the nonmagnetic base is constituted to have the Co convent lower than the Co content of the ferromagnetic metallic thin film of the uppermost layer. The electromagnetic conversion characteristics of high-frequency range signals are, therefore, assured by the ferromagnetic metallic thin film of the uppermost layer. Corrosion is prevented by the ferromagnetic metallic thin film of the lowermost layer. Since the coercive force of the lowermost layer is low, the electromagnetic conversion characteristics of low-frequency range signals are improved. The high corrosion resistance and the high electromagnetic conversion characteristics in a wide frequency range are obtd. in this way.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a magnetic recording medium, and more particularly, the present invention relates to a magnetic recording medium containing Co and Ni as main components, or containing Co, Ni and C as main components.
The present invention relates to a horizontal recording type magnetic recording medium in which a ferromagnetic metal thin film containing r as a main component is supported on a nonmagnetic substrate by vapor deposition.

<Conventional technology> In recent years, magnetic recording media have become increasingly dense, and in particular, magnetic recording media that use ferromagnetic metal thin films mainly composed of Co and added with Ni, etc. have a large saturation magnetic flux density (and a low coercive force). Because of its high value, it is being actively researched.

This type of magnetic recording medium can be manufactured by various methods, but a particularly excellent method is proposed to be a multilayer structure in which two or more ferromagnetic metal thin films are laminated on a non-magnetic substrate using an oblique evaporation method. has been done. In the oblique evaporation method, each layer of ferromagnetic metal thin film is produced by directing ferromagnetic metal vapor onto the surface of a non-magnetic substrate at a specific angle using a vapor phase method such as evaporation, thereby separating columnar crystal grains of ferromagnetic metal from other layers. ferromagnetic metal thin film grown in a specific direction intersecting the growth direction of columnar crystal grains (Japanese Patent Publication No. 56-26891.56-42055.63-
21254 and 60-37528, JP-A-54-60
3.54-147010.56~94520°57-3
233.57-30228.57-13519.57-
141027.57-41028.57-141029
．． 57-143730.57-143731.57-1
47129.58-14324.58-50628.6
0-76025.61-110333.6118712
2, 63-10315, 63-10315, 63-
13117, 63-14317.63-14320
and 63-39127, etc.). Although this improves coercive force and other electromagnetic properties or mechanical properties, it is still insufficient.

The present inventors studied magnetic recording media for horizontal recording from various points of view, and found that the growth direction of columnar grains in each ferromagnetic metal thin film, their mutual relationships, the thickness, and their mutual relationships. It was found that the electromagnetic conversion characteristics and durability were insufficient due to insufficient investigation.

In order to solve these problems, the present applicant developed a magnetic recording medium having two layers of Co-Ni ferromagnetic metal thin films in which the growth directions of columnar grains intersect, by making the upper layer thinner and the lower layer thicker. Improved conversion characteristics and durability,
Furthermore, the running performance was improved (Japanese Unexamined Patent Publication No. 63-9015).

However, although this product improves running performance and durability,
Improving electromagnetic conversion characteristics is insufficient.

In addition, as another attempt, in a similar two-layer magnetic recording medium, the minimum incident angle (the angle between the incident direction of the metal particles in the final deposited part of each ferromagnetic metal thin film and the normal to the nonmagnetic substrate) was made. We proposed to improve the electromagnetic conversion characteristics and durability by doing so (Japanese Patent Application Laid-open No. 10314/1983).

On the other hand, the minimum angle of incidence of the upper layer is relatively large, and 2.
Due to the layered structure, the durability, especially under high temperature and high humidity conditions, was poor, and the electromagnetic conversion properties were insufficient.

Furthermore, in obliquely deposited magnetic recording media that have three or more layers of ferromagnetic metal thin films, the thickness of each ferromagnetic metal thin film has not been studied (also, since the incident angle of the metal particles is too large, sufficient electromagnetic conversion characteristics cannot be achieved). There is a problem that it is not possible to obtain a
The thickness of each layer is approximately the same, 500 to 700 mm, and the incident angle of the ferromagnetic metal is 22 to 72 mm in each layer.
There is a problem of inferior corrosion resistance due to the large angle (Japanese Patent Application Laid-Open No. 53-60205). There are problems such as deterioration of electromagnetic conversion characteristics (JP-A-63-39127, JP-A-63-103).
Publication No. 15).

In addition, oxidation causes cupping (warpage in the tape width direction) in the magnetic tape, which tends to cause output fluctuations due to changes in spacing with the magnetic head.

<Problems to be Solved by the Invention> The present invention has been made in view of the above circumstances, and is an obliquely deposited magnetic recording medium having a multilayered ferromagnetic metal thin film, which has high electromagnetic conversion characteristics and is suitable for use under high temperature and high humidity conditions. The purpose of the present invention is to provide a magnetic recording medium that satisfies both durability and durability.

Means for Solving the Problems> The above objects are achieved by the following inventions (1) to (7).

(1) It has a magnetic layer formed by oblique vapor deposition on a nonmagnetic substrate, and this magnetic layer is composed of at least two ferromagnetic metal thin films, and this ferromagnetic metal thin film is composed of Co13 and N
A magnetic recording medium containing i as a main component or containing Co, Ni, and Cr as main components, in which the Co content of the ferromagnetic metal thin film in the bottom layer is the Co content in the ferromagnetic metal thin film in the top layer. A magnetic recording medium characterized by lower than .

(2) Co content of the ferromagnetic metal thin film in the bottom layer is 70 to 8
The magnetic recording medium according to (1) above, which has a content of 5 at%.

(3) Co content of the top layer ferromagnetic metal thin film is 75 to 9
The magnetic recording medium according to (1) or (2) above, wherein the magnetic recording medium is 0 at%.

(4) If the angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is the incident angle, the maximum value of the incident angle is θmax, and the minimum value of the incident angle is θmin, then the bottom layer The magnetic recording medium according to any one of (1) to 3) above, wherein the ferromagnetic metal thin film is deposited at θmax smaller than θmax during deposition of the uppermost ferromagnetic metal thin film.

(5) If the angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is the incident angle, the maximum value of the incident angle is θll1aX, and the minimum value of the incident angle is θmin, then the top layer The magnetic recording medium according to any one of (1) to 4) above, wherein the ferromagnetic metal thin film is deposited at θmin which is larger than θmin when the ferromagnetic metal thin film of the bottom layer is deposited.

(6) θmax and θm when depositing the top layer of ferromagnetic metal thin film
The sum of in and θm at the time of depositing the ferromagnetic metal thin film of the bottom
The magnetic recording medium according to (4) or (5) above, which is larger than the sum of ax and θmin.

(7) According to any one of (1) to 6) above, comprising two ferromagnetic metal thin films deposited such that the direction in which the ferromagnetic metal is incident intersects with the normal line of the nonmagnetic substrate interposed therebetween. magnetic recording media.

Effect> The magnetic recording medium of the present invention has a magnetic layer composed of at least two ferromagnetic metal thin films on a nonmagnetic substrate. This ferromagnetic metal thin film has Co and Ni as its main components, or Co, Ni, and Cr as its main components.

In the present invention, among these ferromagnetic metal thin films, the lowest layer,
That is, the Co content of the ferromagnetic metal thin film closest to the nonmagnetic substrate is configured to be lower than the Co content of the uppermost ferromagnetic metal thin film.

The reason for this is as follows.

Nonmagnetic substrates usually contain oxygen and moisture, which penetrate into the ferromagnetic metal thin film from the substrate surface. For this reason, corrosion of the ferromagnetic metal thin film tends to progress from the non-magnetic substrate side.

Furthermore, in general, low frequency signals are recorded deep in the magnetic layer, and high frequency signals are recorded in a shallow region. For example, Hi
-8 standard video distribution, low frequency signal (0.75MH)
When a high frequency signal (chrominance signal of 7.0 MHz) and a high frequency signal (luminance signal of 7.0 MHz) are recorded in a superimposed manner, normally, the low frequency signal is mainly recorded on the bottom layer.

In a ferromagnetic metal thin film containing CO as a main component, the lower the Co content, the better the C oxidation property, but the lower the coercive force He.

Therefore, in the magnetic recording medium of the present invention, the electromagnetic conversion characteristics of high frequency signals are ensured by the top layer ferromagnetic metal thin film with high Hc due to the high Co content, and the top layer with high corrosion resistance is ensured due to the low Co content. Corrosion is prevented by the ferromagnetic metal thin film in the lower layer, and the coercive force of the lowermost layer is low, resulting in good electromagnetic conversion characteristics for low-frequency signals.

Therefore, the magnetic recording medium of the present invention has high corrosion resistance (and high electromagnetic conversion characteristics in a wide band).

By the way, in forming a ferromagnetic metal thin film on an obliquely deposited magnetic recording medium such as the magnetic recording medium of the present invention, a nonmagnetic substrate is placed on the surface of a rotating cylindrical cooling drum while being conveyed. Vapor deposition is performed by irradiating a ferromagnetic metal source with an electron beam or the like.

At this time, the angle between the direction in which the ferromagnetic metal is incident and the normal to the surface of the non-magnetic substrate is called the angle of incidence, and the deposition is normally performed so that the angle of incidence gradually decreases from the start to the end of the deposition. Therefore, the columnar crystal grains in the ferromagnetic metal thin film formed on the non-magnetic substrate are approximately parallel to the non-magnetic substrate surface on the non-magnetic substrate side, and grow in an arc shape as they move away from the non-magnetic substrate surface.

The maximum value and minimum value of the incident angle during vapor deposition are referred to as maximum incident angle θmax and minimum incident angle θmin, respectively.
Note that θmax is 90 degrees or less, and the vapor deposition efficiency is θmax
It increases from x to θmin.

In a horizontal recording type magnetic recording medium in which the magnetic layer is magnetized in the in-plane direction, θmax is set to 90 degrees. This is θ
This is because the larger max is, the smaller the average inclination of the columnar crystal grains with respect to the surface of the nonmagnetic substrate is, and the Hc in the in-plane direction of the ferromagnetic metal thin film is improved.

In the present invention, if the ferromagnetic metal thin film of the bottom layer is deposited at θmax smaller than θwax when depositing the top layer,
That is, if the bottom layer is deposited at θmax of less than 90 degrees, the corrosion resistance is further improved.

The reason for this is as follows.

As a result of repeated experiments, the inventors found that θmax around 90 degrees,
In other words, they discovered that the deposition efficiency is low in areas where the ferromagnetic metal is incident parallel to the surface of the non-magnetic substrate, so the diameter of the columnar crystal grains becomes smaller and voids are created between each grain.
It was discovered that oxygen and moisture in the nonmagnetic substrate penetrated through these gaps, causing corrosion to progress.

Therefore, by depositing the bottom layer at θmax as described above, the generation of the voids can be suppressed and a magnetic recording medium with extremely good corrosion resistance can be obtained. Furthermore, since the voids are reduced, the filling rate of the ferromagnetic metal in the thin film is improved, and high saturation magnetization can be obtained.

Moreover, even if the bottom layer is deposited at a small θmax and Hc becomes low, the electromagnetic conversion characteristics regarding the low-frequency signal mainly recorded in the bottom layer will be improved.

Furthermore, θmax when depositing the top layer is equal to θm when depositing the bottom layer.
Since it is larger than ax, Hc of the uppermost layer is improved, and electromagnetic conversion characteristics of high frequency signals are improved. Therefore, the effects of the present invention in that high electromagnetic conversion characteristics can be obtained in a wide band and high corrosion resistance can be realized are further improved.

Further, even when the uppermost layer of the ferromagnetic metal thin film is deposited at θmin which is larger than the θmin when the lowermost layer of the ferromagnetic metal thin film is deposited, the effects of the present invention are further improved.

θmin is also involved in the inclination of the columnar crystal grains, and when θmin is large, the average inclination of the columnar crystal grains becomes small, so that He is improved. On the other hand, when θ+nin is small, the average slope becomes large, and since most of the columnar crystal particles are vapor-deposited with high efficiency, the diameters of the columnar crystal particles become nearly uniform, making it difficult for voids to form between each columnar crystal particle. As a result, a dense film can be obtained.

For this reason, θmin during the top layer deposition and the bottom layer deposition
If the above relationship is established, the Hc of the top layer can be made high (and the Hc of the bottom layer can be made relatively low), so the electromagnetic conversion characteristics can be improved over a wide band, and the corrosion resistance of the bottom layer can be improved. can be improved.

Furthermore, in this case, if the relationship between θwax at the time of depositing the bottom layer and θmax at the time of depositing the top layer is as described above, the electromagnetic conversion characteristics and corrosion resistance will be even higher.

In each of the above cases, if the sum of θmax and θmin during the deposition of the ferromagnetic metal thin film of the top layer is greater than the sum of θmax and θmin during the deposition of the bottom layer, higher electromagnetic conversion characteristics and corrosion resistance are achieved. do.

<Specific configuration> Hereinafter, the specific configuration of the present invention will be explained in detail.

[Nonmagnetic Substrate] There is no particular restriction on the material of the nonmagnetic substrate used in the present invention, and various films that can withstand the heat during deposition of a ferromagnetic metal thin film, such as polyethylene terephthalate, can be used.

Further, various materials described in Japanese Patent Application Laid-Open No. 10315/1988 can be used.

[Magnetic Layer] The magnetic layer formed on the nonmagnetic substrate is composed of two or more ferromagnetic metal thin films formed by an oblique evaporation method.

This ferromagnetic metal thin film has CO and Ni as its main components, or Co, Ni, and Cr as its main components.

In the present invention, C of the ferromagnetic metal thin film of the bottom layer.

The Co content is set to be lower than the Co content of the uppermost ferromagnetic metal thin film.

In this case, the Co content of the ferromagnetic metal thin film in the bottom layer is 7
It is preferably 0 to 85 at%, particularly 74 to 80 at%. When the Co content is less than the above range, it is difficult to obtain the coercive force required for the bottom layer, and when it exceeds the above range, it is difficult to obtain the corrosion resistance required for the bottom layer.

The Co content of the top layer ferromagnetic metal thin film is 75 to 90a.
t%, particularly preferably 79 to 85 at%.
When the Co content is less than the above range, it is difficult to obtain the coercive force required for the top layer, and when it exceeds the above range, it is difficult to obtain the corrosion resistance required for the top layer.

The main constituent elements other than CO of the ferromagnetic metal thin film are Ni, or Ni and Cr.
Various metals and other metal components described in Publication No. 315 and the like may be contained as necessary, and Ar and the like contained in the film forming atmosphere may be contained.

The content of these elements is 5 at% of the ferromagnetic metal thin film.
It is preferable that it is below.

The content ratio of Ni and Cr is not particularly limited and may be set appropriately depending on the purpose, but it is preferable that the Cr content in the ferromagnetic metal thin film is 10 at % or less.

Furthermore, if necessary, a small amount of oxygen may be included in the surface layer,
Corrosion resistance can also be improved.

In such a magnetic layer, it is preferable that the lowermost ferromagnetic metal thin film is deposited at θWaX smaller than θmax when the uppermost ferromagnetic metal thin film is deposited. This improves both corrosion resistance and electromagnetic conversion characteristics.

In this case, θmax when depositing the top layer is preferably 80 to 90 degrees, particularly preferably 85 to 90 degrees, and θmax when depositing the bottom layer is preferably 31 to 89 degrees, particularly 60 to 84 degrees.

Further, it is preferable that the ferromagnetic metal thin film of the uppermost layer is deposited at θmin which is larger than θmin when the ferromagnetic metal thin film of the lowermost layer is deposited.

Such a configuration also improves both corrosion resistance and electromagnetic conversion characteristics.

In this case, θmin during deposition of the top layer is preferably 20 to 60 degrees, particularly preferably 31 to 60 degrees, and θll1in during deposition of the bottom layer is preferably 10 to 50 degrees, particularly 10 to 30 degrees.

Furthermore, in each of the above cases, it is preferable that the sum of θwax and θwin during the deposition of the ferromagnetic metal thin film of the uppermost layer is larger than the sum of θmax and θl1lin during the deposition of the lowermost layer.

In this case, the sum of θmax and θmin of the lowest layer is 10
It is preferably 0 to 150 degrees, particularly 116 to 150 degrees, and the sum of θmax and θmin of the lowest layer is 4
It is preferably 1 to 139 degrees, particularly 70 to 114 degrees.

Further, it is preferable to have two ferromagnetic metal thin films deposited such that the direction in which the ferromagnetic metal is incident crosses the normal line of the nonmagnetic substrate. In this case, in these two layers, the growth directions of the columnar crystal grains of the ferromagnetic metal intersect with the normal line to the surface of the nonmagnetic substrate interposed therebetween.

Such a structure can be obtained by obliquely depositing the nonmagnetic substrate with its running direction reversed.

In this case, the two layers are preferably the top layer and a layer adjacent thereto, or the top layer and a layer adjacent to the top layer with IN sandwiched therebetween.

With such a configuration, the top layer and other
The layers can each be made of Hc suitable for high frequency signal recording and low frequency signal recording, and electromagnetic conversion characteristics are improved over the entire region.

There is no particular limit to the number of laminated ferromagnetic metal thin films, and a configuration of two, three, or four or more layers may be selected depending on the purpose.

In the case of a multilayer structure with three or more layers, the intermediate layer between the top layer and the bottom layer should be designed to have optimal He and corrosion resistance, taking into account various conditions such as the frequency band of the recording signal and the thickness of each layer. The θmax, θmin, thickness, growth direction of columnar crystal grains, etc. during vapor deposition may be appropriately designed so as to obtain the desired results.

For example, when a low frequency signal and a high frequency signal are recorded in a superimposed manner as in the Hi-8 standard, each of the above conditions may be determined in consideration of the frequency band of the signal mainly recorded in each layer.

Preferably, the thickness of each ferromagnetic metal thin film is about 400 to 1000 thick. If the thickness of the top layer becomes thinner than 400, high-frequency signals of, for example, about 7.0 MHz cannot be recorded sufficiently, resulting in a decrease in output. On the other hand, if it becomes thicker than 1000 people, noise increases and the signal-to-noise ratio decreases.

Note that the thickness of the entire magnetic layer is preferably 2000 Å or more. As a result, the output in the low frequency range of about 0.75 MHz can be made sufficiently thick.

Further, in order to obtain high output in both the low and high ranges, it is preferable that the thickness increases from the top layer to the bottom layer.

Each ferromagnetic metal thin film is formed by an oblique vapor deposition method. Since the oblique vapor deposition apparatus and method are described in the various documents mentioned above, any one may be adopted from among them.

In the oblique deposition method, for example, a long film-like nonmagnetic substrate is unwound from a supply roll and fed along the surface of a rotating cooling drum, while diagonal deposition is performed from one or more stationary metal sources, and It is something that is rolled up. In this case, the incident angle is from θmax at the initial stage of deposition to θmin at the final stage.
Columnar crystal grains of a ferromagnetic metal whose main component is Co are grown in an arc shape on the surface of a nonmagnetic substrate and aligned.

If the magnetic layer has a multilayer structure, this step is repeated.

When forming a two-layer ferromagnetic metal thin film in which the direction of incidence of the ferromagnetic metal crosses the normal line of the nonmagnetic substrate, it is possible to perform oblique deposition with the running direction of the nonmagnetic substrate reversed. good.

Various known top coat layers are preferably provided on the magnetic layer of the magnetic recording medium of the present invention in order to protect the magnetic layer and improve corrosion resistance. Furthermore, in order to ensure runnability when formed into a tape, it is preferable that various known back coat layers be provided on the side of the nonmagnetic substrate opposite to the magnetic layer.

The magnetic recording medium of the present invention is suitable for various types of magnetic recording that require high-density recording, but is suitable for recording in which high-frequency signals and low-frequency signals are superimposed, such as in Hi-8 standard video recording. Particularly effective.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Example 1] In an Ar atmosphere of 10-'Torr, a polyethylene terephthalate (PET) film with a thickness of 7p was fed out from a supply roll and moved along the circumferential surface of a rotating cylindrical cooling drum. A ferromagnetic metal thin film was formed by diagonally depositing metal and wound onto a take-up roll.

Next, this winding roll is used as a supply roll, and PET
A magnetic recording medium having a two-layered magnetic layer was obtained by obliquely depositing a ferromagnetic metal in an incident direction intersecting the incident direction in the above-mentioned oblique deposition with the normal direction of the film surface interposed therebetween.

Samples shown in Table 1 below were obtained by changing the composition of the ferromagnetic metal used to form the upper layer and the lower layer. Note that the upper layer and the lower layer were made of a Co-Ni alloy, and Table 1 shows only the CO content.

The thickness of the upper layer of each sample is 900 people, and the thickness of the lower layer is 11 people.
00 people, θmin was 30 degrees, and θmax was 90 degrees during the deposition of the upper and lower ferromagnetic metal thin films.

These samples were cut with a slitter and made into tape.
It was a Hi-8 standard video cassette.

The following evaluations were performed for each sample.

The results are shown in Table 1.

(1) Rust generation After storage for one week in an environment of 60° C. and 90% RH, the degree of discoloration on the magnetic layer side of the tape was visually determined. The evaluation criteria were as follows.

0: No change ○: Discoloration to pale yellow △; Discoloration to yellow ×: Discoloration to blue (2) Cupping After storing for one week at 60°C and 90% RH, place the tape on a flat surface and remove the tape in the tape width direction. The warp height h at the end was measured. The evaluation criteria were as follows.

Q:　h　　＝.

Q: O < h 50.2 mm △: 0.2 < h < 0.5 mm ×: h 20.5 mm Cupping is an indicator of the degree of deformation in the tape width direction, and if cupping is large, the tape and magnetic head will be damaged. The spacing cannot be kept constant, resulting in output fluctuations.

(3) Electromagnetic (electromagnetic conversion characteristics at 0.75 MHz and 7 MHz) Hi-8 standard VTR (7) 5ONY EV-S9
00, a single signal of 0.75 MHz and 7 MH
The RF ratio output of the RF ratio output reference tape when a single signal of z was recorded was compared, and judgment was made based on the following evaluation criteria.

Q: (RF specific output≧2.0dB ○:OdB≦(RF specific output<2.0dB△knee 1.0d
B≦(RF specific output<0dBX:(RF specific output<-1,0
dB Note that the relative moving direction of the magnetic head during the measurement was the direction in which the growth direction of the columnar crystal grains in the upper layer was projected onto the PET film surface.

Note that the sample No. shown in Table 1 above.

Samples 1-1.1-3 are reference samples for comparison, and the compositions of the upper and lower layers are set to be exactly the same.

In Table 1 above, the sample of the present invention in which the Co content of the ferromagnetic metal thin film in the bottom layer is lower than the Co content in the ferromagnetic metal thin film in the top layer achieves high corrosion resistance, and High electromagnetic conversion characteristics are obtained in all high frequencies.

On the other hand, comparative sample No. 1-1, in which both the upper layer and the lower layer have a low Co content, has good corrosion resistance but poor electromagnetic conversion characteristics, particularly extremely poor characteristics at 7 MHz.

In addition, in comparison sample No. 1-3, in which both the upper layer and the lower layer have a high Co content, the corrosion resistance is low, and the
．． 75M) Poor electromagnetic conversion characteristics at Iz.

[Example 2] Each sample shown in Table 2 below was obtained by changing θwin and θwax during vapor deposition of the upper and lower ferromagnetic metal thin films. Note that sample No. 2-1 is the same as sample No. 1-2 shown in Table 1, and the θm of other samples is
Configurations other than in and θwax are sample No. 2-
It is the same as 1.

For each of these samples, the same evaluation as in Example 1 and the following evaluation were performed. The results are shown in Table 2.

(4) ΔBm The maximum magnetization Bm after one week of storage at 60° C. and 90% RH was measured, and the increase relative to the initial Bm was determined.

(5) Do (dropout) aging change 50℃・80
Dropout after one week of storage was measured at %RH, and the increase rate relative to the initial dropout was determined.

In addition, a dropout was determined when the output decreased by 16 dB or more and the output decreased by 15 μsee D.

(6) Change in running friction over time The dynamic friction coefficient μ was measured after storage for one week at 50° C. and 80% RH, and the rate of increase with respect to the initial μ was determined.

In Table 2 above, samples No. 2-1, 2-5, and 2-8 are reference samples for comparison, and the formation conditions for the upper layer and the lower layer are set to be exactly the same.

Sample N where θmax of the lower layer is smaller than θmax of the upper layer
In No. 2-2, the corrosion resistance is significantly improved compared to sample No. 2-1, in which all incident angles other than θmax in the lower layer are the same. No.

The electromagnetic conversion characteristics are significantly improved compared to 2-8.

In addition, in sample No. 2-3, where θmin in the upper layer is larger than θmin in the lower layer, all incident angles other than θmin in the upper layer are the same.

Sample N has significantly improved electromagnetic conversion characteristics compared to 2-1, and all incident angles other than θmin in the lower layer are the same.
Corrosion resistance is significantly improved compared to No. 2-5.

Sample No. 2-4 that satisfies these same conditions
has extremely high corrosion resistance and electromagnetic conversion characteristics.

[Example 3] According to Example 1, a magnetic recording medium sample having a magnetic layer composed of three ferromagnetic metal thin films shown in Table 3 below was prepared.

However, the thickness of the upper layer, middle layer and lower layer is 7.
00 people, 700 people, and 700 people, and θ at the time of vapor deposition of each layer.
win and θmax were the same as in Example 1.

In addition, the deposition direction of each layer (growth direction of columnar crystal grains) shown in Table 3 is indicated as 10 if the direction when projected onto the tape surface is the same direction as the relative movement direction of the magnetic head with respect to the tape. , when in the opposite direction, - is displayed.

Each of these samples was evaluated in the same manner as in Example 1. The results are shown in Table 3.

From the results shown in Table 3, it is clear that the effects of the present invention are achieved even in a three-layered magnetic layer.

[Example 4] θ during vapor deposition of upper layer, intermediate layer, and lower layer ferromagnetic metal thin films
Each sample shown in Table 4 below was obtained by changing min and θmax. Note that sample No. 4-1 is the sample No. shown in Table 3.

Same as 3-2, θmin and θ of other samples
Configurations other than max are sample No.

Same as 4-1.

Each of these samples was evaluated in the same manner as in Example 2. The results are shown in Table 4.

From the results shown in Table 4, it is clear that the effects of the present invention are also achieved in a three-layered magnetic layer.

Although a Co-Ni alloy was used for the magnetic layer in each of the above embodiments, the CO content, θmin,
Effects equivalent to those of each of the above examples were observed depending on θmax.

<Effects of the Invention> The magnetic recording medium of the present invention has extremely good corrosion resistance.
Therefore, there is very little change in the magnetic properties over time, and since the occurrence of cupping is suppressed, there is very little change in the spacing between the medium and the magnetic head over time. Furthermore, there is very little dropout or change in runnability over time when it is made into a tape (it has excellent durability and reliability).

Moreover, the magnetic recording medium of the present invention has extremely good electromagnetic conversion characteristics over a wide band from low frequency signals to high frequency signals.

For this reason, frequency range Particularly suitable for wide recording.

Out wish Man TDC Co., Ltd. teenager Reason Man

Claims (7)

[Claims] (1) It has a magnetic layer formed by oblique vapor deposition on a nonmagnetic substrate, and this magnetic layer is composed of at least two ferromagnetic metal thin films, and this ferromagnetic metal thin film is made of Co and Ni.
or Co, Ni, and Cr as main components, wherein the Co content of the ferromagnetic metal thin film in the bottom layer is lower than the Co content in the ferromagnetic metal thin film in the top layer. A magnetic recording medium characterized by low magnetic flux. (2) Co content of the ferromagnetic metal thin film in the bottom layer is 70 to 8
The magnetic recording medium according to claim 1, wherein the content is 5 at%. (3) Co content of the top layer ferromagnetic metal thin film is 75 to 9
The magnetic recording medium according to claim 1 or 2, wherein the magnetic recording medium has a content of 0 at%. (4) If the angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is the incident angle, the maximum value of the incident angle is θmax, and the minimum value of the incident angle is θmin, then the bottom layer 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic metal thin film is deposited at θmax smaller than θmax when the uppermost ferromagnetic metal thin film is deposited. (5) If the angle between the direction in which the ferromagnetic metal is incident during vapor deposition and the normal to the surface of the non-magnetic substrate is the angle of incidence, the maximum value of the incident angle is θmax, and the minimum value of the incident angle is θmin, then the top layer 5. The magnetic recording medium according to claim 1, wherein the ferromagnetic metal thin film is deposited at θmin greater than θmin at the time of depositing the ferromagnetic metal thin film of the bottom layer. (6) θmax and θm when depositing the top layer of ferromagnetic metal thin film
The sum of in and θm at the time of depositing the ferromagnetic metal thin film of the bottom
Claim 4 or 5 larger than the sum of ax and θmin
The magnetic recording medium described in . (7) Magnetic recording according to any one of claims 1 to 6, comprising two ferromagnetic metal thin films deposited such that the direction of incidence of the ferromagnetic metal intersects with the normal line of the non-magnetic substrate. Medium.