JPH0321967B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application] The present invention is an improvement of a magnetic recording medium having a low coercive force layer made of a magnetic thin film on a nonmagnetic substrate and a magnetic recording layer made of a perpendicular magnetic layer having an axis of easy magnetization perpendicular to the film surface. and an improved method for manufacturing magnetic recording media. [Prior Art] The above-mentioned two-layer magnetic recording medium consisting of a low coercive force layer and a perpendicular magnetization layer was developed as a perpendicular magnetic recording medium that can be efficiently recorded by a unipolar head in the perpendicular magnetic recording system. −91 Publication, Special Publication 1987
-Proposed in Publication No. 10764, etc. This proposed magnetic recording medium with a two-layer film structure (hereinafter referred to as a "dual-layer film medium") is specifically created by the RF bipolar sputtering method, with the low coercive force layer made of permalloy and the perpendicular magnetization layer made of Co (copal). )-Cr (chromium) alloy film, and is excellent in that it can obtain high recording sensitivity and large playback output, but further improvements are desired in terms of recording sensitivity, playback output, etc. There is. [Object of the invention] The present invention aims to improve the characteristics of the above-mentioned two-layer film medium, and is made of a low coercive force layer, particularly a permalloy thin film containing Ni (nickel) and Fe (iron) as main components. To provide a magnetic recording medium having further improved high recording sensitivity, large reproduction output, and uniform characteristics over a wide area by combining the characteristics of a low coercive force layer and a perpendicular magnetization layer, and a method for manufacturing the same. It is. [Structure, operation and effect of the invention] The magnetic recording medium of the present invention includes the above-mentioned two-layer film medium,
That is, in a magnetic recording medium having a low coercive force layer made of a magnetic thin film of a soft magnetic material such as permalloy on a nonmagnetic substrate, and a magnetic recording layer having an axis of easy magnetization perpendicular to the film surface, the low coercive force layer is It consists of a plurality of laminated magnetic thin films, and each magnetic thin film is laminated so that the directions of its hard magnetization axes are different from each other so that the overall in-plane recording/reproducing characteristics are uniform. This is a characteristic feature. The above-mentioned present invention was made as follows. It is thought that the smaller the coercive force of the low coercive force layer of a two-layer film medium, the more advantageous it is in terms of recording sensitivity, etc.
When we created and evaluated a disk using a magnetic recording medium made of permalloy thin film with a small coercive force of 5 Oe (Oersted) or less, the envelope of its playback output changed, and in terms of stable playback, it ended up reaching its lowest point. After various studies, it was discovered that the cause of the problem was the in-plane magnetic anisotropy of the permalloy thin film constituting the low coercive force layer. In other words, the above-mentioned magnetic recording medium with a permalloy thin film as a low coercive force layer has a higher reproduction output when recording and reproducing by running the permalloy thin film in the direction of the axis of hard magnetization than when running in the direction of the axis of easy magnetization. It was discovered that this structure has a large value and exhibits good characteristics, especially in the high frequency range of high-density recording. Therefore, with the above structure, the in-plane magnetic anisotropy of the low coercive force layer as a whole is reduced, so the reproduction output is The lowest point of increases and the envelope becomes uniform within the plane and becomes stable. As a result, a magnetic recording medium suitable for a disk system with high recording density and uniform recording and reproducing characteristics in the plane can be obtained. Note that in-plane magnetic anisotropy refers to magnetic anisotropy in a plane parallel to the film surface. In view of the above, the present invention provides that the thin film constituting the low coercive force layer is made of permalloy (which may contain a third component such as Mo (molybdenum), Cu (copper), etc.) having a low coercive force of 5 Oe or less. This is particularly effective in the case of soft magnetic materials that exhibit in-plane magnetic anisotropy in a region of low coercive force. Further, a thin film whose coercive force in the direction of the hard axis of magnetization is smaller than the coercive force in the direction of the easy axis is effective. Furthermore, a thin film with a high magnetic permeability is preferably used from the viewpoint of recording sensitivity and reproduction output. Although it is preferable from the manufacturing point of view that each thin film be made of the same soft magnetic material, it is clear from the above points that thin films made of different soft magnetic materials may be combined to form a low coercive force layer. In addition, as a magnetic recording layer, of course the perpendicular magnetic layer made of the Co-Cr alloy film of the embodiment, but also the perpendicular magnetization layer made of W (tungsten).
Co-Cr added with a third element such as Ta (tantalum)
It is clear from the spirit of the present invention that the present invention can be applied to alloys and other known perpendicular magnetization layers. It is also obvious that the present invention can also be applied to a structure in which an adhesive layer or the like is formed between each layer. By the way, the low coercive force layer of the above-mentioned magnetic recording medium can be manufactured by simply regulating the substrate transport direction when forming each thin film of the low coercive force layer according to the second aspect of the present invention described below. That is, the second invention is characterized in that each of the thin films is formed by a facing target sputtering method while the substrate is being transferred in a direction that is perpendicular to the direction of the difficult magnetization axis of the thin film to be formed. It is. The second invention is based on the discovery that when a film is formed by facing target sputtering, an axis of difficult magnetization is formed in a direction perpendicular to the facing direction of the targets. In addition, the above-mentioned facing target sputtering method is
According to the sputtering method known in Japanese Patent Application Laid-open No. 57-158380, etc., a substrate is placed on the side of a pair of targets arranged facing each other, and a magnetic field for plasma trapping is applied vertically between the targets to perform sputtering. , refers to the sputtering method for forming a film on a substrate. Hereinafter, the details of the above-mentioned present invention will be explained based on examples. FIG. 1 is a structural diagram of a facing target sputtering apparatus used in the practice of the present invention. As is clear from the figure, this device was developed in the above-mentioned JP
It has basically the same structure as the opposed target sputtering device known in Japanese Patent No. 158380. That is, in the figure, 10 is a vacuum chamber, 20 is an evacuation system consisting of a vacuum pump etc. for evacuating the vacuum chamber 10, and 30 is a system for introducing a predetermined gas into the vacuum chamber 10 to raise the pressure inside the vacuum chamber 10 to 10 ^-1 ~ This is a gas introduction system that is set to a predetermined gas pressure of approximately 10 ^-4 Torr. In the vacuum chamber 10, a pair of targets T ₁ and T ₂ are held by target holders 15 and 16 fixed to the side plates 11 and 12 of the vacuum chamber 10 via insulating members 13 and 14 as shown in the figure. The surfaces T _1S and T _2S to be sputtered are arranged so as to face each other in parallel with a space in between. And target T ₁ ,
T ₂ and its corresponding target holder 15,
16, targets T ₁ , T ₂ , permanent magnets 152 ,
162 is cooled. The magnets 152 and 162 are disposed so that their north and south poles face each other with the targets T ₁ and T ₂ in between, so that the magnetic field is directed towards the targets T 1 and T ₂ .
Formed only in the direction perpendicular to T ₂ and between targets. Note that 17 and 18 are insulating members 13 and 1
4 and target holders 15 and 16 from plasma particles during sputtering, and to prevent abnormal discharge in areas other than the target surface. Further, a substrate holding means 41 for holding a substrate 40 on which a magnetic thin film is formed is provided in the vacuum chamber 10 on the side of the targets T ₁ and T ₂ . Substrate holding means 4
Reference numeral 1 denotes a feed roll 41a, a support roll 41b, and a take-up roll 41, which are supported rotatably and parallel to each other by support brackets (not shown).
It consists of three rolls of c, and the sputtering surface is placed so that the substrate 40 faces the space between targets _T1 and _T2 .
It is arranged so as to be held in a direction substantially perpendicular to T _1S and T _2S . Therefore, the substrate 40 is the winding roll 4
1c, it is movable in a direction perpendicular to the sputtering surfaces T _1S and T _2S . Note that the surface temperature of the support roll 41b can be adjusted. On the other hand, a power supply means 50 consisting of a DC power source for supplying sputtering power has its positive side connected to the ground and its negative side connected to the targets T ₁ and T ₂ , respectively. Therefore, the sputter power from the power supply means 50 is supplied between the anode and the cathode, with the ground as the anode and the targets T ₁ and T ₂ as the cathodes. In order to protect the substrate 40 during press sputtering, a shutter (not shown) is provided between the substrate 40 and the targets T ₁ and T ₂ to move in and out. As mentioned above, the structure is basically the same as that of the above-mentioned Japanese Patent Application Laid-open No. 57-158380, and as is known, high-speed low-temperature sputtering is possible. That is, in the space between the targets T ₁ and T ₂ , sputter gas ions, γ electrons emitted by the sputter, etc. are bound by the action of the magnetic field, and a high-density plasma is formed. Therefore, sputtering of the targets T ₁ and T ₂ is promoted, the amount of deposition increases from the space, the deposition rate on the substrate 40 increases, high sputtering occurs, and the substrate 40
0 is on the side of the targets T ₁ and T ₂ , low-temperature sputtering is also possible. Note that the opposed target sputtering method of the present invention is not limited to the above-mentioned apparatus;
As mentioned above, this is a sputtering method in which a substrate is placed on the sides of a pair of targets facing each other, and a perpendicular magnetic field is applied between the targets to perform sputtering to form a film on the substrate. Therefore, the magnetic field generating means may also be an electromagnet instead of a permanent magnet. Further, the magnetic field may be of any type as long as it confines γ electrons etc. in the space between the targets, and therefore it also includes the case where it is generated not over the entire surface of the target but only around the target. In FIG. 1, the traveling direction (MD) of the substrate 40 is the direction in which the targets T ₁ and T ₂ face each other, that is, the direction in which the permanent magnets 152 and
The magnetic flux φ generated by the magnetic field generator consisting of 162
It will be in almost the same direction as . The embodiment shown in FIG. 2 is different from that shown in FIG. 1 only in the substrate holding means 41, and the direction of the magnetic flux φ, that is, the opposing direction of the targets T ₁ and T ₂ and the traveling direction (MD) of the substrate 40 are almost perpendicular to each other. The substrate holding means 41 is configured as follows. Therefore, if the width direction of the substrate 40 is referred to as TD, the magnetic flux φ and the width direction TD are approximately parallel to each other. Next, an embodiment of a perpendicular magnetic recording medium according to the present invention implemented using the above-mentioned facing target type spartan device will be described. The crystal structure of the obtained alloy film was identified using a counting X-ray diffraction device manufactured by Rigaku Corporation, and the vertical orientation was determined by the hexagonal close-packed structure and the rocking curve of the (002) plane peak using the X-ray diffraction method described above. Obtained using the device, its half width △
Evaluation was performed at θ ₅₀ . The film thickness and composition were determined from a curve calibrated in advance using a fluorescent X-ray device manufactured by Rigaku Denki. The magnetic properties of the medium are measured using a vibrating sample magnetometer (Toei Kogyo).
KK). The recording and playback characteristics of double-layer film media were
The evaluation was carried out using a vertical magnetic head similar to the one known in Japanese Patent Application No. 58-91. Example 1 After forming a low coercive force layer made of permalloy on a substrate under the following conditions, a perpendicular magnetization layer made of Co--Cr was sequentially formed to prepare a two-layer film medium. A Apparatus conditions A-1 Low coercive force layer a Target T ₁ and T ₂ materials: Both T ₁ and T ₂ are Mo-
Permalloy of 4Wt%, Ni-78Wt%, Fe-18Wt% b Substrate 40: 50 μm thick polyethylene terephthalate (PET) film c Target T ₁ , T ₂ spacing: 120 mm d Magnetic field on target surface: 100 to 200 Gauss e Target T ₁ , _T2 shape: 100mmL×150
Rectangular shape of mmW×12mmt f Distance between substrate 40 and ends of targets _T1 and _T2 : 20mm A-2 Co-Cr perpendicular magnetization layer a Target material: Both _T1 and _T2 are Co-80Wt
%, Cr-20Wt% alloy target c Target T ₁ , T ₂ spacing: 160 mm d Target surface magnetic field: 100 to 200 Gauss e Target T ₁ , T ₂ shape: 100 mm L x 150
Rectangular shape f of mmW x 12 mmt Distance between substrate 40 and ends of targets T ₁ and T ₂ : 20 mm B Operation procedure The following operations were carried out under the conditions of A-1 and A-2. a After installing the substrate, evacuate the inside of the vacuum chamber 10 until the ultimate vacuum level is 1×10 ^-6 Torr or less. b Introduce Ar (argon) gas to a predetermined pressure, perform press sputtering for 3 to 5 minutes, open the shutter, and perform film formation while transferring the substrate 40 in the opposite direction of the targets T ₁ and T ₂ as shown in the figure. Summer. Note that the Ar gas pressure during sputtering was 4×10 ⁻³ Torr. c The power input during sputtering was 3KW for both A-1 and A-2. C. Results Figure 3 shows the characteristic magnetization characteristics of the low coercive force layer. The magnetization characteristics in the board running direction (MD direction) and the board width direction (TD direction) are different.
Magnetic anisotropy occurred in the plane, with the MD direction being the axis of easy magnetization and the TD direction being the axis of difficult magnetization. Further, Table 1 shows its representative characteristics. In addition, the third
In the figure, H indicates the strength of the applied magnetic field, and B indicates the magnetization of the low coercive force layer.

[Table] In Table 1, HCE and HCH are the coercive forces in the directions of the easy axis of magnetization and the axis of hard magnetization, respectively. A-2 on the low coercive force layer having the characteristics shown in Table-1.
Table 2 shows the characteristics of the perpendicular magnetization layer consisting of a Co-Cr layer formed under these conditions.

【table】

[Table] In Table 2, vertical coercive force refers to the coercive force perpendicular to the medium film surface, and horizontal refers to the coercive force parallel to the medium film surface. Note that the coercive force was measured by separating the low coercive force layer of the two-layer film medium. The half-width Δθ ₅₀ was measured as is in the double-layered film medium. D Electromagnetic Conversion Characteristics As shown in FIG. 4, rectangular samples were cut out in the MD direction and the TD direction for the two-layer film media having the characteristics shown in Tables 1 and 2, and the electromagnetic conversion characteristics of each were evaluated. The measurement results are shown in Table 3 and Figure 5. Fifth
In the figure, the horizontal axis shows the number of magnetic flux reversals per inch (FRPI) as the recording density D, and the vertical axis shows the reproduction output voltage Ep. The electromagnetic conversion characteristics were determined by running the tape at 4.75 cm/sec during recording and at 9.5 cm/sec during playback.

[Table] As shown in Table 3, by recording and reproducing in the direction of the hard axis of magnetization of the low coercive force layer, the reproduction output is 1.3 to 1.5 times larger than that in the direction of the easy axis of magnetization. It turned out that. In addition, FIG. 6 shows the cutting direction θ shown in FIG.
50KFRPI and 100KFRPI of samples that changed
The figure shows the reproduction output equivalent to that in the TD direction if the angle is approximately 60 degrees or more with respect to the MD direction. Example 2 A low coercive force layer was formed using the sputtering apparatus shown in FIG. 2 under conditions A-1 of Example 1. In the obtained low coercive force layer, the traveling direction (MD direction) of the substrate 40 was the axis of hard magnetization, and the width direction (TD direction) of the substrate 40 was the axis of easy magnetization. Next, after forming the low coercive force layer in the same manner as in Example 1, a Co--Cr layer was formed using the sputtering apparatus shown in FIG. 1 under the conditions A-2 of Example 1. When the electromagnetic conversion characteristics were evaluated in the same manner as in Example 1, it was found that the reproduction output Ep was better when recording and reproducing in the direction of the axis of hard magnetization than when recording and reproducing in the direction of the axis of easy magnetization.
was large, and as in Example 1, the improvement was remarkable. The characteristics of the low coercive force layer are shown in Table 4.
HCE/HCV>1.

[Table] Example 3 As a low coercive force layer, the permalloy layer of Example 1 was first formed using the sputtering device shown in FIG. 1, and then the same permalloy layer was formed thereon using the sputtering device shown in FIG. A two-layer low coercive force layer was formed in accordance with Example 2, with the hard magnetization axes of each layer perpendicular to each other. Next, a perpendicular magnetization layer made of a Co--Cr layer was formed using the sputtering apparatus shown in FIG. 1 in accordance with Example 1. Thus, MD direction and TD for the obtained medium
After evaluating the electromagnetic conversion characteristics in each direction, we found that
Uniform playback output with almost no directionality of MD and TD Ep
I got it. In addition, the playback output Ep is as shown in Example 1.
It was the intermediate value of the reproduction output Ep in the MD and TD directions.
Therefore, it can be seen that by stacking thin films having magnetic anisotropy so that their hard axes of magnetization are in different appropriate directions, it is possible to reduce the anisotropy in recording and reproducing as a whole. In addition, since the playback output Ep when stacked is an intermediate value,
Each layer is considered to make an additive contribution. Afterwards,
When stacking, the direction of the hard axis of magnetization of each layer is determined by the sixth
Referring to the relationship between the cutting direction θ and the playback output in the figure,
It can be seen that the selection should be made so that recording and playback are uniform.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of the facing target sputtering device used in the implementation of the present invention, Figure 3 is an explanatory diagram of magnetic characteristics, Figure 4 is an explanatory diagram of sample cutting, and Figure 5 is an example of an embodiment. FIG. 6 is a graph showing the measurement results of the electromagnetic conversion characteristics of No. 1, and FIG. 6 is a graph showing the relationship between the sample cutting direction and the reproduction output. T ₁ , T ₂ : Target, 10: Vacuum chamber, 20:
Exhaust system, 30: Gas introduction system, 40: Substrate, 50:
Spatuta power supply.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium having a low coercive force layer made of a magnetic thin film on a nonmagnetic substrate and a magnetic recording layer having an axis of easy magnetization perpendicular to the film surface, wherein the low coercive force layer is laminated. It consists of a plurality of magnetic thin films, and each magnetic thin film is laminated so that the direction of its hard axis of magnetization is different from each other so that the in-plane recording/reproducing characteristics are uniform as a whole. magnetic recording media. 2. The magnetic recording medium according to claim 1, wherein the low coercive force layer is a two-layer film laminated such that the hard magnetization axes of the magnetic thin films are orthogonal to each other. 3. The magnetic recording medium according to claim 1 or 2, wherein the coercive force of each of the magnetic thin films in the direction of the hard axis of magnetization is smaller than the coercive force in the direction of the easy axis of magnetization. 4 A low coercive force layer consisting of multiple magnetic thin films laminated in different directions on a non-magnetic substrate so that the direction of the hard axis of magnetization reduces the in-plane anisotropy as a whole, and magnetization perpendicular to the film plane. In a method for manufacturing a magnetic recording medium having a magnetic recording layer having an easy axis,
A magnetism characterized in that each magnetic thin film of the low magnetic force layer is formed by a facing target sputtering method while moving the substrate in a direction perpendicular to a direction in which the opposing direction of the target and the axis of difficult magnetization of the magnetic thin film to be formed are perpendicular. Method of manufacturing recording media. 5. The low coercive force layer is composed of two layers stacked such that the hard magnetization axes of the magnetic thin films are orthogonal to each other, one layer of which is formed by transferring the substrate in the same direction as the target, and the other layer is formed by transferring the substrate in the same direction as the target. 5. The method of manufacturing a magnetic recording medium according to claim 4, wherein the layer is formed by transporting the substrate in a direction perpendicular to the direction in which the target faces.