JPS59157832A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a vertical magnetic recording medium having high sensitivity and high durability by providing a protecting layer having wear resistance and high sliding performance on a continuous magnetic layer containing mainly iron oxide with a specific ratio between the intra-surface residual magnetization and the vertical residual magnetization of a magnetic layer. CONSTITUTION:A continuous magnetic layer 10 containing mainly iron oxide which is easily magnetized vertically with >=0.5 MV/MH between the intra-surface residual magnetization and the vertical residual magnetization of a magnetic layer is deposited at a high speed on a substrate 6 by a counter target sputtering device, etc. without exposing the substrate 6 directly to plasma and at a low temperature of the substrate 6. Then a protective layer 11 made of an inorganic material such as Al2O3, SiC, etc. or silicone oil, carbon black graft polymer, fluorine polymer, etc. having high wear resistance and high sliding performance is formed on the layer 10. Thus it is possible to obtain a magnetic recording medium having high durability and small aging of the reproduction output owing to the combination with the layer 10 having high corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Industrial Application Field 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 used for video, audio,
It is widely used for recording various electrical signals such as digital ones. 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 increase in the density of magnetic recording, recording methods that use magnetization in the longitudinal direction in the plane have a tendency to increase the demagnetizing field within the medium as the recording signal becomes shorter in wavelength, resulting in attenuation and rotation of the residual magnetization. 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 Electric pnics J
August 7, 1978 issue Nn192).

According to this recording method, as the recording wavelength becomes shorter, the demagnetizing field that acts on the residual magnetization in the medium decreases.
It has favorable characteristics and is considered to be an inherently suitable method for high-density recording.

By the way, K, which efficiently performs such perpendicular recording,
The recording layer of the magnetic recording medium is perpendicular (thickness direction of the magnetic layer)
It must have an axis of easy magnetization. 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 media includes Co
, Fe304, γFQ203, Co-added Fe3
04- Co-doped γ-Fe, 03, hexagonal ferrite (
For example, barium ferrite)-MnBt, etc. are used as magnetic powders (JP-A-52-46803, No. 5
No. 3-67406, No. 52-78403, No. 55-8
No. 6103, No. 52-78403, No. 54-8720
2 publications). However, in these coated media, since a non-magnetic binder is present in the magnetic layer, there is a limit to increasing the density of the packed layer of magnetic powder, 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 applying a magnetic material onto 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.

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 PM, and in particular, the PM content is 5□ to 25% by weight of C.
It is said that the o-Cr alloy film is superior.

In addition, a magnetic recording medium having a magnetic layer formed by adding 30% by weight or less of p-dium to a Co-Cr alloy film was disclosed in Japanese Patent Laid-Open No. 55
-111110, and further includes a cobalt-vanadium alloy film (e.g., Institute of Electrical and Electronics Communication Engineers: abbreviated as IE).
Transactionon M, an academic journal published by EE
agnetism” 1982 Vol. 18 Yang 6.1116
Magnetic recording media using a cobalt-ruthenium alloy film (for example, the 18th Tohoku University Research Symposium ``Perpendicular Magnetic Recording'' held in March 1982) are known.

However, as a result of studies conducted by the present inventors, it has been found that the magnetic recording medium having the structure described above is insufficient for practical use because the Co'-Cr-based perpendicularly magnetized film has the following drawbacks. I found that.

(11. 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"-' Torr or higher, and the substrate must be subjected to advanced cleaning treatment and low spatter. Conditions such as speed are required, and the control factors for vertical alignment become very complicated.

(2) During signal recording and reproduction, since the magnetic recording medium and the perpendicular recording/reproducing head slide relative to each other, the interface between the head and the medium is poor and scratches occur on the medium. This can easily cause damage to the head.

(3) Because the magnetic layer is hard, cracks tend to occur when it is provided on a flexible substrate; (4) Corrosion resistance as a magnetic recording medium is not sufficient; It is necessary to provide a protective film on the surface.

(5) The raw material cobalt 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 recording medium that is suitable for high-density perpendicular magnetic recording, has excellent mechanical strength and chemical stability, and has good magnetic properties. We succeeded in obtaining a medium.

4. Structure of the invention and its effects, that is, the present invention provides a magnetic recording medium having a magnetic layer, wherein the magnetic layer (a) consists of a continuous magnetic layer containing iron oxide as a main component.

(b), residual magnetization (MH) in the in-plane direction of the magnetic layer;

The ratio (My/MH) of the surface pressure of the magnetic layer to the residual magnetization (Mv) in the perpendicular direction is 0.5 or more.

The present invention relates to a magnetic recording medium characterized in that the magnetic recording medium has the following configurations, and a protective layer having good wear resistance and slipperiness is provided on the magnetic layer.

According to the present invention, since the magnetic layer is mainly composed of iron oxide, excellent characteristics unique to oxides (i.e. mechanical strength, chemical stability, etc.) can be obtained, and compared to conventional alloy thin films. The necessary surface peritoneal membrane is no longer necessary. As a result, the distance between the magnetic head and the medium can be reduced, making it possible to perform high-density recording.In addition, it is possible to reduce costs in terms of materials. Since the residual magnetization ratio (MY/Ml) in the in-plane direction and the perpendicular direction is set to 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. The structure is such that magnetization can be achieved with sufficient pressure. The magnetization amount MV=MH can be measured, for example, with a sample vibrating magnetometer (manufactured by Toei Kogyo Co., Ltd.). That is, MY/MH is 05
If it is less than that, it is difficult to obtain a magnetic moment suitable for perpendicular magnetization.

Furthermore, in addition to the above-mentioned iron oxide-based magnetic layer, the magnetic recording medium of the present invention is provided with a layer with good wear resistance and slipperiness as a protective layer for this magnetic layer, so that magnetic This effectively prevents the magnetic layer surface from being abraded during high-speed sliding with the head and reducing the S/N ratio of the reproduced output.

In other words, if the above-mentioned protective layer is not provided, both the magnetic head and the medium side are likely to be damaged, but the presence of the protective layer prevents damage to the medium side due to its good wear resistance. , and its good slipperiness prevents damage to the head side and improves running performance.

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 iron oxide (e.g. Fe, 0
4. γ-Fed O, or a beltlide compound consisting of a non-stoichiometric composition intermediate between these) itself is a continuous thin film (with a large saturation magnetization and a low coercive force (HC)).
consists of too to 5oooooe). In this magnetic layer, the sum of both elements iron and oxygen is 5
It is preferable that the amount is on a 0 weight plate, and more preferably 70% by weight or more.

Further, the ratio of iron and oxygen is preferably 'number of oxygen atoms/number of iron atoms = 1 to 3, more preferably 473 to 2, and the iron oxides exemplified above are suitable. .

When the above iron oxide has a spinel crystal structure (for example, it is preferable that the surface is oriented perpendicular to the in-plane direction), the amount of saturation magnetization is large, and the reproduction of recorded signals is possible. Sometimes, the residual magnetic flux density is large and the reproduction sensitivity is extremely good. In general, iron oxides that exhibit magnetism include α-Fe203, which has parasitic ferromagnetism in a rhombohedral crystal structure, Fe3O4, γ-Fe2O3, and their berthride compounds, which exhibit ferrimagnetism in a spinel structure, and hexagonal oxides. There are rare earth garnet type ferrites having a Ba-based ferrite, Sr ferrite, pb ferrite, or its derivative nigernet structure. Among these iron oxides, the saturation magnetization, which is one of the important magnetic properties, is 2.0 GauOs for α-Fe203, and 380 Gaus at maximum for Ba ferrite, Sr7 elite, and PB ferrite.
about s, and even more so for garnet type ferrites, at most l
40 Gauss. On the other hand, the saturation magnetization of the spinel type ferrite preferably used in the present invention is 48
0 Gauss and is the largest among iron oxides. Such a large amount of saturation magnetization is extremely effective when reproducing a recorded signal because it provides a sufficient residual magnetic flux density and improves reproduction sensitivity. On the other hand, there are Ba ferrite and Sr7 elite that exhibit saturation magnetic flux densities similar to spinel type ferrite (K), but in order to form these continuous thin film magnetic layers, 1. It is unsuitable because it has to be kept at a high temperature of 500° C., which limits the type of substrate (for example, plastic substrates with poor heat resistance cannot be used). 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, or compounds of non-metals and semimetals are added to the magnetic layer, which improves the magnetic properties of the magnetic layer (e.g. coercive force, saturation magnetization, residual magnetization, etc.). It is possible to improve the amount of magnetization), its crystallinity, and the orientation of the crystal in a specific axis direction.

Such additive elements or compounds include ACCO-C0-
Mn, Zn, Co-Zn%Ll, Cr, Ti,
Lt-Cr, Mg, Mg-Ni, Mn-Zn,
Ni, N1-AA, N1-Zn, Cu, Cu-Mn,
Examples include Cu-Zn and V, but other elements and compounds may also be used.

In addition, the constituent materials of the protective layer include Lj, Be
.

C, Na, Mg, ACSt, P, Ca, Sc,
TI, V, Cr, Mn.

Fe-Co, Ni, Cu, Zn%Ga, Ge,
Ss%Rh, Y, Zr, Nb.

Mo, Ru, Rh-Pd, Ag, Cd, In,
Sn, Te, Ba, Cs.

Hf + Ta, W, Re, Os, Ir-Pt%
Inorganic elements such as Au, compounds thereof, oxides, nitrides, and combinations thereof can be used. Among these, Al,
0. , S[C1TIC, etc. are preferred, and oxide-based materials are preferred because of their good stability. However, materials that exhibit magnetism are undesirable because they have an adverse effect on magnetic properties.

The protective layer may also be composed of an organic compound such as silicone oil, carbon black graft polymer, monobasic fatty acid having 12 to 16 carbon atoms, or monobasic fatty acid having 12 to 1 carbon atoms.
6 fatty acid esters of monohydric alcohols. Or, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylic CX
2) IJ copolymer, acrylic ester-acrylic nitrile copolymer, phenol resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, high molecular weight polyester resin and Mixtures of cyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate polymers, fluorine-based polymers such as Teflon, electron beam irradiation-curable unsaturated prepolymers, such as mannic anhydride type, urethane acrylic type, polyester acrylic type Polymer compounds such as polyether acrylic type, polyurethane acrylic type, poly7mide acrylic type, and pun polymer can be used.

The thickness of the protective layer is 100X to 5μm (preferably 200X
~3 μm) K is preferably selected, because if it exceeds 5 μm, the output will tend to decrease and the electromagnetic conversion characteristics will deteriorate, while if it is less than 100×, it will be too thin and the effect will be poor. In the case of an inorganic protective layer, vacuum evaporation or sputtering is used.

It can be formed by plating, etc., and in the case of organic materials, it can be formed using the dipping method, reverse rule coating method, curtain coating method, gravure coating method, nozzle coating method, and dung-soaking method.

It can be formed by electron beam polymerization, plasma polymerization, etc. The organic protective layer can be formed to a desired thickness by dissolving an organic compound in a suitable solvent, coating it to a thickness of 1 to 10 μm, and drying with hot air to evaporate the solvent.

Furthermore, in the present invention, various materials can be used for the base material that can be used to provide the magnetic layer.

For example, as a substrate exhibiting desirable surface smoothness, it is possible to use a substrate made of plastics such as polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycafubonate, polyimide, polymethyl methacrylate, ceramics such as glass, and the like. Alternatively, metal substrates may also be used. The shape of the substrate 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 the magnetic material can be deposited while the substrate is running; therefore, K is.

Sputtering methods, vapor deposition methods, etc. are applied in which a magnetic material target is sputtered in a processing chamber connected to an evacuation system such as a vacuum pump, or the material is evaporated from a magnetic material evaporation source and deposited on the substrate. It is possible. In either case,
The elements constituting the magnetic layer may be flown to form a continuous thin film on the substrate.

5. Examples Hereinafter, the magnetic recording medium of the present invention will be explained in more detail with reference to the drawings. Approximately 1 μm iron oxide (Fes
A perpendicularly magnetized film 10 is formed, and a perpendicularly magnetized film 10 is formed.
A protective layer 11 of CCR (or Mo, W, A40H, S jot) is formed to a thickness of 400K.

The protective layer 11 can be formed by a vacuum evaporation method using electron beam heating.

In order to form a perpendicularly magnetized film (magnetic layer) 1O, a method for depositing a magnetic material on a substrate is a vacuum evaporation method (including electric field evaporation and ion blating method) in which the atoms constituting the magnetic layer are caused to fly. , sputtering method, etc. Among these methods, a method using a facing target sputtering device is preferable.

FIG. 2 shows a facing target sputtering apparatus.

In the drawing, 1 is a vacuum chamber, 2 is an exhaust 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 to 10-' Torr.
This is a gas introduction system that is set to a certain level.

The target electrodes are configured as opposed target electrodes in which a pair of targets (T1 and Tt) are arranged parallel to each other and are separated from each other by a target holder 4. A magnetic field is formed between these targets by a 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 buttons between the opposing targets.

In the sputtering apparatus configured in this way, a magnetic field is formed in a direction perpendicular to the surfaces of both targets T, , T, which face each other in parallel, and this magnetic field causes the cathode descending part (i.e., the target) T, -T2 to be The γ electrons emitted by the gR bombardment of the sputtering gas ions accelerated by the electric field in the region between the plasma atmosphere generated in between and the targets TI and T on the target surface are confined in the space between the targets, Move towards the other target.
The γ electrons that have moved to the other target surface are reflected at the cathode fall section nearby. In this way, the γ electrons repeat reciprocating motion while being constrained by magnetic field pressure between T and -T. During this reciprocating motion, the γ electrons collide with the neutral atmospheric gas to generate ions and electrons in the atmospheric gas, and these products are γ-electrons from the target.
Promote electron emission and ionization of atmospheric gas. Therefore, high-density plasma is formed in the space between the targets T and -T, and the target material is sputtered under sufficient pressure as a cleaning body, and is deposited as a magnetic material on the substrate 6 on the side. It turns out.

This facing target sputtering device is superior to other flying means and is capable of high deposition rate film formation by high speed sputtering, and the substrate is not directly exposed to plasma.
It is advantageous for forming a perpendicularly magnetized film because it is possible to form a film at a low substrate temperature. Moreover, since 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, the material is easily deposited directionally in the desired direction, making it possible to record perpendicular magnetization. It becomes easier to obtain a membrane with a structure suitable for

Next, a specific example of producing a magnetic recording medium using the above sputtering apparatus will be described.

The conditions for this preparation were as follows.

Target material Iron (contains 1m of Co) Substrate Glass Facing target spacing 100mm Magnetic field in sputtering space 1000e Target shape 100mm diameter disk (5mm
Thickness) Distance between substrate and target end 30mm Back pressure in vacuum chamber 10-' Torr Introduced gas
Ar+O.

Introduced gas pressure: 4 x 10"-' Torr Sputter input power: 420 W In this way, a magnetic recording medium having an iron oxide magnetic layer 10 on the base 6 was obtained as shown in FIG. 1. Regarding this medium, Characteristics of the magnetic layer were evaluated by identifying the composition using an X-ray microanalyzer (XMA) and determining the state of iron oxide using X-ray diffraction.

The magnetic properties were determined using a sample shaker IIJJ type magnetometer. The characteristics of the obtained magnetic recording medium were as follows.

First, the ratio of residual magnetization i (MH) in the in-plane direction to residual magnetization i (M”/) in the direction perpendicular to the plane is MY/MU≧0.5
Met. 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 the time was defined as Myo and MV. From this, it is clear that the former hysteresis curve is smaller than the latter hysteresis curve, and MV≧0.5MH, indicating that a magnetic layer suitable for perpendicular magnetization is formed. . This is a surprising fact for iron oxide-based magnetic layers.

In addition, the composition of this magnetic recording medium was determined using
As a result of measurement using an EX-7000 model, it was found that Fe was the main peak and a small amount of Co was contained.

Furthermore, in order to investigate the state of iron oxide, measurements were performed using an X-ray diffraction device (manufactured by JEOL Ltd. "JDX-10RAJ: CuKc<tube used)", as shown in the table below.
(It was found that the other layer in 1 is mainly composed of iron oxide. Furthermore, electron microscopy revealed that this magnetic layer has an ordered structure in the direction perpendicular to the in-plane direction. It was observed in

(The following margin continues on the next page) Note that before film formation by the above sputtering method, the surface of the substrate may be subjected to surface cleaning treatment by bombarding it with Ar in the same sputtering device, or may be subjected to baking. It is desirable to perform surface treatment by applying high frequency.

In the magnetic recording medium obtained as described above, it is important that the axis of easy magnetization of the magnetic layer 10 can be made almost perpendicular to the in-plane direction thereof, and that the protective layer 11 is provided on the surface thereof. .

That is, a magnetic recording medium according to the present invention in which various protective layers 11 are disposed on the magnetic layer 1O, and a magnetic recording medium in which there is no such protective layer and the magnetic layer 10 or Co-Cr perpendicular magnetization film protrudes 1 cjil from the surface side. In the meantime, we conducted a driving test and a durability test. In the running test, a disk-shaped magnetic recording medium was brought into contact with a magnetic head and run 500 times.
This was done by measuring the decrease in reproduction output. In the durability test, the head load was set to 1509, the medium was run 100 times, the surface condition of the medium was observed, and the peeling condition of the magnetized film was examined under a microscope. The results of these tests were as shown in the table below.

(The following margin continues on the next page) From these results, it can be seen that when a protective layer is provided on the magnetized film according to the present invention, the reproduction output and durability are significantly improved. It can be seen that in the case of no protective layer, an iron oxide magnetized film is better than a Co--Cr magnetized film, but in the present invention, the characteristics can be further improved by using a -11J film. In addition, among the above as a protective layer, Aj! 20g,
5if2. It is understood from the above results that ceramics such as SiC and TiC are good, but oxides are superior in terms of chemical stability and the like. Further, the protective layer containing carbon black has the effect of preventing the surface of the medium from being charged.

Next, because the magnetic recording medium according to the present invention uses a magnetic layer containing iron oxide as a main component, it
It has significantly superior chemical and mechanical stability compared to Cr-based magnetic layers. Figure 4 shows the forced deterioration test (80°C, 85°C).
%R) Residual magnetic flux density (Br) measured by a sample vibrating magnetometer (manufactured by Toei Kogyo Co., Ltd.) of the medium according to the present invention using an iron oxide-based magnetic layer, which has a reduced pressure when performing t) Fig. 3 shows the change over time (IL) of the magnetic layer and the change over time (b) 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, B
It can be seen that the deterioration of r is significantly reduced. Note that the reason why ΔB r /Br decreases somewhat in the iron oxide magnetic layer is that part of the film composition Fe5Q4 is γ-Fe, O
This is thought to be due to the transition to . In addition, the 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 changes were observed in the surface condition of the iron monoxide magnetic layer. I couldn't.

[Brief explanation of the drawing]

The drawings illustrate the present invention, and FIG. 1 is a cross-sectional view of a magnetic recording medium, FIG. 2 is a schematic cross-sectional view of a facing target sputtering apparatus, FIG. 3 is a hysteresis curve diagram of the magnetic recording medium, and FIG. The figure is a graph showing a comparison of changes over time in residual magnetic flux densities of magnetic recording media. In addition, in the symbols shown in 1 drawing, 1...... Vacuum chamber 2...
Self... Exhaust system 3... Gas introduction system 4.5...
・・・・・・・・・Holder 6・・・・・・・・・・・・
...Base 10...Magnetic layer 11...Protective layer T, , T,...Target be. Agent Patent attorney Hiroshi Aisaka (and 1 other person) Figure 1 Figure 3 Figure 4 Forced assault ΔShun (lllI)

Claims (1)

[Claims] l. A magnetic recording medium having a magnetic layer, wherein the magnetic layer comprises (lL) a continuous magnetic layer containing iron oxide as a main component. (b), residual magnetization (MH) in the in-plane direction of the magnetic layer; The ratio (MY/MH) to the residual magnetization (CMV) in the direction perpendicular to the plane of the magnetic layer is 0.5 or more. What is claimed is: 1. A magnetic recording medium comprising: a protective layer having good abrasion resistance and slipperiness provided on the magnetic layer.