JPH0315246B2 - - Google Patents

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. 2. Prior Art Conventionally, this type of magnetic recording medium has been widely used for recording in various telecommunication systems such as video, audio, and digital. These have been developed as a system that uses magnetization in the in-plane longitudinal direction of a magnetic layer (magnetic recording layer) formed on a substrate. However, in recent years, with the increasing density of magnetic recording, recording methods that use magnetization in the in-plane longitudinal direction have the problem of attenuation and rotation of the residual magnetization due to the increase in the demagnetizing field within the medium as the recording signal becomes shorter in wavelength. This causes a significant decrease in playback output. For this reason, it is extremely difficult to reduce the recording wavelength to submicron or less. On the other hand, a perpendicular magnetization recording method that uses magnetization in the thickness direction of the magnetic layer of a magnetic recording medium (so-called perpendicular magnetization) has recently been proposed (for example, "Nikkei Electronics" August 7, 1978, No. .192).
According to this recording method, as the recording wavelength becomes shorter, the demagnetizing field that acts on the residual magnetization in the medium decreases, so it has favorable characteristics for increasing density, and is essentially suitable for high-density recording. This method is considered to be suitable for By the way, in order to perform such perpendicular recording efficiently, the recording layer of a magnetic recording medium must have an axis of easy magnetization in the perpendicular direction (thickness direction of the magnetic layer). Such a magnetic recording medium is a coated type in which a magnetic coating mainly composed of magnetic powder and a binder is coated on a substrate (support), and the axis of easy magnetization is oriented in the perpendicular direction of the magnetic layer. The medium is known. This coated medium contains Co,
Fe ₃ O ₄ , γ-Fe ₂ O ₃ , Co-added Fe ₃ O ₄ , Co-added γ-
Fe ₂ O ₃ , hexagonal ferrite (e.g. barium ferrite), MnBi, etc. are used as magnetic powders (Japanese Patent Application Laid-open Nos. 52-46803, 53-67406, 52
-78403, 55-86103, 52-78403, same
54-87202). However, in these coated media, there is a limit to increasing the packing density of magnetic powder due to the presence of a non-magnetic binder in the magnetic layer, and therefore it is difficult to increase the S/N ratio sufficiently. I can't. Moreover, the magnitude of the recorded signal is limited by the size of the magnetic particles, and thus a medium having a magnetic layer made of a magnetic coating is unsuitable for perpendicular magnetization recording. Therefore, continuous thin film magnetic recording media, in which a perpendicularly magnetized magnetic layer is formed by continuously depositing a magnetic material on a support without using a binder, are attracting attention as suitable for high-density recording. ing. This continuous thin film type perpendicular magnetization recording medium is
For example, as disclosed in Japanese Patent Publication No. 57-17282, it has a magnetic recording layer made of an alloy film of cobalt and chromium, and in particular, a Co-Cr alloy film with a chromium content of 5 to 25% by weight is used. It is said to be excellent.
Further, a magnetic recording medium having a magnetic layer formed by adding 30% by weight or less of rhodium to a Co-Cr alloy film is disclosed in JP-A-55-111110, and furthermore, a cobalt-vanadium alloy film (for example, Communication Society: Abbreviation: An academic journal published by IEEE, “Transaction on
Magnetism" 1982 Vol. 18 No. 6, p. 1116) and cobalt-ruthenium alloy films (for example, the 18th Tohoku University Research Symposium "Perpendicular Magnetic Recording" Paper Collection held in March 1982). Are known. On the other hand, for example, JP-A-54-51804 discloses that a Fe-Ni soft magnetic (low coercive force) underlayer is provided between the Co-Cr perpendicular magnetization film and the substrate. . In this case, the presence of the soft magnetic underlayer allows the magnetic flux from the auxiliary magnetic pole to be concentrated on the opposing main magnetic pole, and is expected to have the effect of reducing the demagnetization effect in the residual magnetization state after recording. can. However, as a result of studies conducted by the present inventor, it was found that the magnetic recording medium having the above structure is insufficient for practical use because the Co-Cr-based perpendicularly magnetized film has the following drawbacks. I discovered something. (1) In order to orient the axis of easy magnetization perpendicular to the plane of the magnetic layer, it is necessary to create the magnetic layer in a high vacuum of 10 ^-7 Torr or higher, and the substrate must be cleaned with advanced cleaning treatment and low sputtering speed. etc., and the control factors for vertical alignment become extremely complicated. (2) When recording and reproducing signals, the magnetic recording medium and the perpendicular recording/reproducing head slide relative to each other, so the interface between the head and the medium is poor and scratches may occur on the medium. This can easily cause damage to the head. (3) Since the magnetic layer is hard, cracks tend to occur when the magnetic layer is provided on a flexible substrate. (4) Corrosion resistance as a magnetic recording medium is insufficient;
Therefore, it is necessary to provide a protective film on the surface. (5) Cobalt, a raw material, is difficult to obtain stably and is expensive. 3. Purpose of the Invention In view of the above-mentioned circumstances, the present inventor has made extensive studies and has developed a magnetic material that is suitable for high-density perpendicular magnetic recording, has excellent mechanical strength and chemical stability, and has excellent recording/reproducing characteristics. We succeeded in obtaining a recording medium. 4 Structure of the Invention and its Effects That is, the present invention provides a magnetic recording medium in which a magnetic layer is provided on a substrate, in which the substrate itself is formed of a high magnetic permeability material and is in direct contact with the high magnetic permeability substrate. The magnetic layer is formed by: (a) aluminum, cobalt, cobalt-manganese, zinc, cobalt-zinc, lithium, chromium, titanium, lithium-chromium, magnesium, magnesium-nickel, manganese-zinc, Formed by the opposed target sputtering method using iron as a target material containing an additive selected from the group consisting of nickel, nickel-aluminum, nickel-zinc, copper, copper-manganese, copper-zinc and vanadium. (b) The ratio (M _V /M _H ) of the residual magnetization in the in-plane direction (M _H ) to the residual magnetization (M _V ) in the direction perpendicular to the plane is 0.5 or more, and ( c) A magnetic recording medium comprising a continuous magnetic thin film containing the additive substance and having iron oxide as a main component. According to the present invention, since the magnetic layer contains iron oxide as a main component, excellent characteristics unique to oxides (i.e., mechanical strength, chemical stability, etc.) can be obtained,
The surface protective film required for conventional alloy thin films is no longer required. As a result, the distance between the magnetic head and the medium can be reduced, making it possible to perform high-density recording, and also to reduce costs in terms of materials. Moreover, the residual magnetization ratio (M _V /M _H ) in the in-plane direction and in the perpendicular direction of the magnetic layer whose main component is iron oxide is
Since the value is 0.5 or more, the magnetic moment of the iron oxide magnetic material rises in the perpendicular direction by 30 degrees or more with respect to the in-plane direction, and the structure is such that perpendicular magnetization can be sufficiently realized. The magnetization amounts M _V and M _H can be measured, for example, with a sample vibrating magnetometer (manufactured by Toei Kogyo Co., Ltd.). That is, if M _V /M _H is less than 0.5, it is difficult to obtain a magnetic moment suitable for perpendicular magnetization. In addition, the magnetic recording medium of the present invention has the base itself made of a high magnetic permeability material in addition to the above-mentioned iron oxide-based magnetic layer, so that it concentrates magnetic flux during recording compared to a magnetic layer alone. , and the demagnetization effect after recording can be reduced to improve recording retention. In other words, since the high magnetic permeability substrate has the property of allowing magnetic flux to easily pass through, it is effective in concentrating the magnetic flux from the magnetic pole in the magnetic layer and retaining residual magnetization sufficiently through the magnetic reflux effect described below. Therefore, recording/reproducing sensitivity can be improved without impairing recording density. In this case, since the substrate itself is made of a material with high magnetic permeability, the substrate is made in advance from a material with a predetermined magnetic permeability, and then a film is formed on the substrate in one film forming process (opposing target sputtering). A perpendicularly magnetized film can be formed. Therefore, there is no need to attach a high magnetic permeability film, and all that is needed is a high magnetic permeability substrate, which simplifies the production of magnetic recording media, and also ensures the magnetic concentration and reflux effects due to the high magnetic permeability. be able to. Each layer of the magnetic recording medium of the present invention is constructed as follows. First, the magnetic layer is fundamentally different from conventional coated magnetic layers in that it is made of non-stoichiometric amounts of iron oxide (e.g. Fe ₃ O ₄ , γ-Fe ₂ O ₃ , or intermediate compositions) without the use of a binder. The bertolide compound (having a theoretical composition) itself consists of a continuous thin film (with a large saturation magnetization and a coercive force (H _c ) of 100 to 5000 Oe). In this magnetic layer, the sum of both elements iron and oxygen is preferably at least 50% by weight of the magnetic layer, and more preferably at least 70% by weight. In addition, the ratio of iron to oxygen is preferably 1 to 3 (number of oxygen atoms/number of iron atoms), and even more preferably 4/3 to 2, and the iron oxides listed above are suitable. be.
The above iron oxide has a spinel-type crystal structure (especially, for example, the (111) plane in Fe ₃ O ₄ or the (100) plane in γ-Fe ₂ O ₃ is oriented perpendicular to the in-plane direction). ), the amount of saturation magnetization is large, the residual magnetic flux density is large during reproduction of recorded signals, and the reproduction sensitivity is extremely good. In general, magnetic iron oxides include α-Fe ₂ O ₃ which has parasitic ferromagnetism in a rhombohedral crystal structure; exhibits ferrimagnetism in a spinel structure.
Fe ₃ O ₄ , γ-Fe ₂ O ₃ or their bertholide compounds; hexagonal oxides such as Ba-based ferrite, Sr ferrite, Pb ferrite or derivatives thereof; and rare earth garnet-type ferrites with a garnet structure. Among these iron oxides, the saturation magnetization, which is one of the important magnetic properties, is α-Fe ₂ O ₃
So 2.0 Gauss, Ba ferrite, Sr ferrite,
For Pb ferrite, the maximum is about 380 Gauss, and for garnet type ferrite, the maximum is 140 Gauss.
It is. On the other hand, the saturation magnetization of the spinel ferrite preferably used in the present invention is 480 Gauss.
It is the largest of all iron oxides. Such a large amount of saturation magnetization is extremely effective when reproducing a recorded signal because it ensures a sufficient residual magnetic flux density and improves reproduction sensitivity.
On the other hand, Ba ferrite and Sr ferrite exhibit saturation magnetic flux densities similar to spinel ferrite, but in order to form continuous thin film magnetic layers of these, it is necessary to raise the temperature of the substrate to 500°C using a sputtering device, which will be described later. This poses problems in the production conditions, such as the need to maintain the temperature at a high temperature, which limits the type of substrate (for example, plastic substrates with poor heat resistance cannot be used), making them inappropriate.
The spinel type iron oxide preferably used in the present invention can be formed into a film at a low temperature of room temperature to 300° C., and is not subject to limitations of the substrate material. However, metals other than iron and oxygen or their oxides, nonmetals, semimetals, or compounds thereof are added to the magnetic layer, thereby improving the magnetic properties of the magnetic layer (e.g. coercive force, saturation magnetization, etc.). It is possible to improve the amount of residual magnetization), its crystallinity, and the orientation of the crystal in a specific axis direction. These additive elements or compounds include Al,
Co, Co−Mn, Zn, Co−Zn, Li, Cr, Ti, Li−
Cr, Mg, Mg-Ni, Mn-Zn, Ni, Ni-Al, Ni
-Zn, Cu, Cu-Mn, Cu-Zn, V, etc. Further, the high magnetic permeability material layer is generally provided between the magnetic layer and the base, but the present invention is characterized in that the base itself is made of a high magnetic permeability material. This high magnetic permeability substrate has the property of easily passing flux (in particular, the magnetic permeability μi is 10 ² or more, preferably
2000 or more, Hc is particularly 10 Oe or less, for example 1 Oe), and the axis of easy magnetization is preferably mainly in the inner surface direction of the magnetic layer. Such high magnetic permeability materials may be soft magnetic materials, such as pure iron, silicon steel, permalloy, supermalloy,
Cu−Zn ferrite, Ni−Zn ferrite, Mn−
Crystals made of Zn ferrite, sendust, miu metal, etc.; Fe-Co, Co-Zr, Co and Ti, Y,
Examples include alloys with Hf, Nb, Ta, or W, and amorphous alloys of transition metals such as Fe, Co, Ni, and semimetals such as Si, B, P, and C. In addition, the thickness of the high magnetic permeability material layer is preferably 0.05 to 5 μm, and 0.1
~3μm is more desirable. That is, below 0.05μm,
This is because if the thickness is too thin, the effect will be poor, and if it exceeds 5 μm, the effect will reach a saturated state and the reproduction output will not improve much. Further, the shape of the substrate that can be used in the magnetic recording medium of the present invention may be a sheet, a card, a disk, a drum, or a long tape. To produce this magnetic recording medium, the substrate can be closely supported on a fixed plate, or a predetermined material can be applied while the substrate is traveling. For this purpose, targets of magnetic material are sputtered using a facing target method in a processing chamber connected to an evacuation system such as a vacuum pump. 5 Examples The magnetic recording medium of the present invention will be explained in more detail below with reference to the drawings. First, in order to understand the present invention, a reference example thereof will be explained. FIG. 1 shows an example of a magnetic recording medium according to the same reference example, which shows a magnetic recording medium with a thickness of approximately
A soft magnetic layer 11 made of permalloy with a thickness of 1 μm is formed, and a perpendicular magnetization film 10 made of iron oxide with a thickness of about 1 μm is laminated thereon. Since the soft magnetic layer 11 is formed by a well-known sputtering method, the method for forming it will not be particularly explained here. In the magnetic recording medium according to this embodiment, the soft magnetic layer 11 is not provided in FIG. 1, and the base body 6 is made of permalloy. In order to form the perpendicular magnetization film (magnetic layer) 10,
A facing target sputtering method is used as a means for depositing the magnetic material onto the substrate. FIG. 2 shows a facing target sputtering device. In the drawing, 1 is a vacuum chamber, 2 is an evacuation system consisting of a vacuum pump etc. for evacuating the vacuum chamber 1, and 3 is an exhaust system that introduces a predetermined gas into the vacuum chamber 1 to raise the gas pressure to 10 ^-1 ~
This is a gas introduction system set at approximately 10 ^-4 Torr. The target electrodes are constructed as opposed target electrodes in which a pair of targets T ₁ and T ₂ are separated from each other by a target holder 4 and are placed facing each other in parallel. A magnetic field is generated between these targets by magnetic field generating means (not shown). On the other hand, the substrate 6 on which the magnetic thin film is to be formed is placed by the substrate holder 5 perpendicularly to the side between the opposing targets. In the sputtering device configured in this way,
A magnetic field is formed in a direction perpendicular to the surfaces of both targets T ₁ and T ₂ facing each other in parallel, and this magnetic field creates a gap between the plasma atmosphere generated between the targets T 1 and T 2 and the cathode fall area (i.e., the plasma atmosphere generated between the targets T ₁ and T _{2 )} . The γ electrons emitted by the impact of sputtering gas ions accelerated by the electric field on the target surface in the region between _T1 and _T2 ) are trapped in the space between the targets and moved toward the other opposing target . The γ electrons that have moved to the other target surface are reflected by the cathode fall section nearby. In this way, the γ electrons repeatedly move back and forth between the targets T ₁ and T ₂ while being constrained by the magnetic field. During this reciprocating motion, the γ electrons collide with the neutral atmospheric gas to generate ions and electrons of the atmospheric gas, and these products promote the release of γ electrons from the target and the ionization of the atmospheric gas. . Therefore, the target
A high-density plasma is formed in the space between T ₁ and _{T 2} , and the target material is sufficiently sputtered and deposited as a magnetic material on the lateral substrate 6 . Compared to other flying methods, this facing target sputtering device enables film formation at a high deposition rate using high-speed sputtering, and the substrate is not directly exposed to plasma, allowing film formation at low substrate temperatures. This method is advantageous for forming a perpendicularly magnetized film. Furthermore, the incident energy of the magnetic film material sputtered onto the substrate by the facing target sputtering device is smaller than that of a normal sputtering device, so that the material is easily deposited directionally in the desired direction, resulting in perpendicular magnetization. It becomes easier to obtain a film with a structure suitable for recording. Next, a specific example of producing a magnetic recording medium using the above sputtering apparatus will be described. The preparation conditions were as follows. Target material Iron (contains 1 atomic % Co) Substrate Glass spacing between opposing targets 100 mm Magnetic field in sputtering space 100 Oe Target shape 100 mm diameter disk (5 mm thickness) Distance between substrate and target end 30 mm Back pressure in vacuum chamber 10 ^-6 Torr Introduced gas Ar + O ₂ Introduced gas pressure 4×10 ^-3 Torr Sputter input power 420W In this way, as shown in FIG.
0 was obtained. Regarding this medium, the characteristics of the magnetic layer were evaluated by identifying the composition using an X-ray microanalyzer (XMA), the state of iron oxide using an X-ray diffraction method, and the magnetic properties using a sample vibrating magnetometer. The characteristics of the obtained magnetic recording medium were as follows. First, the ratio of the residual magnetization in both inward directions (M _H ) and the residual magnetization in the direction perpendicular to the plane (M _V ) is M _V /
M _H ≧0.5. That is, as illustrated in FIG. 3, a hysteresis curve during magnetization in the in-plane direction shown by the broken line and a hysteresis curve during magnetization in the perpendicular direction shown by the solid line were obtained, but when the applied magnetic field is zero The amount of magnetization at that time was defined as M _H and M _V. According to this, it is clear that the former hysteresis curve is smaller than the latter hysteresis curve, and M _V ≧0.5M _H , indicating that a magnetic layer suitable for perpendicular magnetization is formed. I understand. The coercive force was 920 oersted in the vertical direction and 750 oersted in the in-plane direction. This is a surprising fact for iron oxide-based magnetic layers. In addition, the composition of this magnetic recording medium was measured using an XMA (X-ray microanalyzer: "X-556" manufactured by Hitachi, Ltd.).
When measured with KEVEX-7000 model), it was found that Fe was the main peak and a small amount of Co was included. Furthermore, in order to investigate the state of iron oxide, measurements were taken using an X-ray diffraction device (JDX-10RA manufactured by JEOL Ltd., using a CuKα tube), and as shown in the table below, the magnetic layer did not contain iron oxide. Furthermore, it was observed using an electron microscope that this magnetic layer had an ordered structure in the direction perpendicular to the in-plane direction.

[Table] Before forming a film using the sputtering method described above, the surface of the substrate may be cleaned by bombarding it with Ar ⁺ in the same sputtering device, baking, or surface treatment using high frequency. It is desirable to keep it. In order to compare with the experiment described above, the target material was pure iron (without Co) under the above production conditions.
As a result of sputtering _in a similar _manner as
It was 500 oersted in the in-plane direction. In the magnetic recording medium obtained as described above, the axis of easy magnetization of the magnetic layer 10 can be made almost perpendicular to the in-plane direction thereof, and a soft magnetic layer base with high magnetic permeability is provided under the magnetic layer 10. It is important to be present. The following description will be made using the medium according to the reference example shown in FIG. 1 as an example, but the same applies to the medium according to this embodiment. FIG. 4a shows the state during magnetic recording, in which the 12 auxiliary magnetic poles in the figure are excited by a recording signal, and a magnetic field 13 is generated from there toward the medium side. In the soft magnetic layer 11, flux 15 is concentrated in the in-plane direction toward the main magnetic pole 14, and magnetic recording corresponding to the main magnetic pole 14 is performed in the magnetic layer 10. That is, the concentration of magnetic flux from the auxiliary magnetic pole to the main magnetic pole is strengthened, and magnetization by vertical magnetic flux can be performed with high sensitivity. Further, FIG. 4b shows the residual magnetization state after magnetic recording, and due to the existence of the soft magnetic layer 11, the soft magnetic layer 1
A flux 18 flows through the magnet 1, and this magnetic reflux effect (horseshoe magnetization mode) can maintain magnetization and reduce the demagnetization effect. For this reason, it is possible to stably obtain a high-level reproduction output based on perpendicular magnetic recording. In FIG. 5, curve a represents the reproduction output of a magnetic recording medium with a soft magnetic layer, and curve b represents the reproduction output of a magnetic recording medium in which a magnetized film is directly provided on the base without the soft magnetic layer. This is the experimental data shown. As is clear from these results, media with a soft magnetic layer can perform recording at high density, high output, and with good frequency characteristics, whereas when the soft magnetic layer is not provided, the characteristics deteriorate. . For recording and playback, the effective head gap is 0.3 μm and the track width is
A 100 μm ring head was used. It has also been confirmed that the magnetic recording medium according to the present invention exhibits significantly less change in output over time. Curve a in FIG. 6 shows a magnetic recording medium with a soft magnetic layer, and it can be seen that high output can be stably obtained even in a deterioration test. However, when the soft magnetic layer is not provided (curve b), the output decreases. However, this forced deterioration test was conducted on media with a recording density of 30 kilobits/inch (the thickness of the magnetic layer was 5000 kbit/inch).
This was done by measuring the output under conditions of 80°C and 85% RH. Recording/playback of media is
A ring-shaped head with an effective gap of 0.4 μm and a track width of 100 μm was used. Next, since the magnetic recording medium according to the present invention uses a magnetic layer containing iron oxide as the main component, it has significantly superior chemical and mechanical stability compared to conventional Co-Cr magnetic layers. ing. Figure 7 shows the results of a forced deterioration test similar to the one described above, as measured by a sample vibrating magnetometer (manufactured by Toei Kogyo Co., Ltd.) of a medium according to the present invention using an iron oxide magnetic layer. Fig. 3 shows a change over time a in the residual magnetic flux density Br, and a change over time c in the residual magnetic flux density Br of a medium using a Co--Cr magnetic layer (ΔBr is the amount of change in the residual magnetic flux density). According to this, in the iron oxide magnetic layer,
It can be seen that the deterioration of Br is significantly smaller than that of the Co-Cr magnetic layer. In addition, in the iron oxide magnetic layer, △Br/
The reason why Br decreases somewhat is due to the composition of the film.
This is considered to be because a part of Fe ₃ O ₄ was transferred to γ-Fe ₂ O ₃ . In addition, observation results after one month (30 days) showed that spots, cloudiness, rust, etc. had occurred on the surface of the Co-Cr magnetic layer, but no change was observed in the surface condition of the iron oxide magnetic layer. .

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and FIG. 1 is a sectional view of a magnetic recording medium, FIG. 2 is a schematic sectional view of a facing target sputtering device, and FIG. 3 is a hysteresis curve of the magnetic recording medium. Figure, Figure 4a
is a schematic diagram during magnetic recording, Figure 4b is a schematic diagram of the residual magnetization state, Figure 5 is a graph comparing the reproduction characteristics of the magnetic recording medium, and Figure 6 is the change over time in the reproduction characteristics of the magnetic recording medium. FIG. 7 is a graph showing a comparison of changes in residual magnetic flux density of magnetic recording media over time. In addition, in the symbols shown in the drawings, 1...vacuum chamber, 2...exhaust system, 3...gas introduction system, 4, 5
...Holder, 6...Base, 10...Magnetic layer, 1
1...Soft magnetic layer, 12...Auxiliary magnetic pole, 14...Main magnetic pole, _T1 , _T2 ...Target.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer is provided on a substrate, the substrate itself is formed of a high magnetic permeability material, and the magnetic layer is formed in direct contact with this high magnetic permeability substrate. , this magnetic layer contains (a) aluminum, cobalt, cobalt-manganese, zinc, cobalt-zinc, lithium, chromium, titanium, lithium-chromium, magnesium, magnesium-nickel, manganese-zinc, nickel, nickel-aluminum, nickel - formed by a facing target sputtering method using iron as a target material containing an additive selected from the group consisting of zinc, copper, copper-manganese, copper-zinc and vanadium; (b) inner surface; The ratio (M _V /M _H ) of the residual magnetization in the direction (M _H ) to the residual magnetization (M _V ) in the direction perpendicular to the surface is 0.5 or more, and (c) contains the additive substance, A magnetic recording medium characterized by being made of a continuous magnetic thin film whose main component is iron oxide.