JPS59148125A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which is suitable for vertical magnetic recording at a high density and has excellent mechanical strength and chemical stability by forming a magnetic layer of a continuous magnetic layer consisting essentially of an iron oxide having a specific characteristic. CONSTITUTION:A magnetic field perpendicular to the surface of targets T1, T2 in a vacuum vessel 1 of a sputtering device is formed to form plasma of a high density between the targets T1 and T2, thus forming a continuous magnetic layer 10 on a substrate 6. Fe (contg. 1 atom% Co) is used for the target material and Ar+O2 for the gas to be introduced to form a magnetic layer having >=0.5% the ratio of the residual magnetization in the direction perpendicular to the plane of the layer 10 with respect to the residual magnetization in the direction within the plane of said layer and 100Angstrom -5mum layer thickness. The particles are oriented in the direction perpendicular to the surface of the magnetic layer and the magnetic recording medium which is suitable for vertical magnetic recording at a high density and has excellent mechanical strength and chemical stability, etc. is obtd.

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 of the plane,
As the recording signal becomes shorter in wavelength, the demagnetizing field within the medium increases, causing attenuation and rotation of the residual magnetization, resulting in a significant reduction in the reproduction 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 J.
August 7, 1978 issue 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 is considered to be a method.

By the way, in order to perform this kind of perpendicular recording efficiently,
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. medium is known. This coated media includes Co, F
ego, r-Fe205, Co-added Fe50. Co-added -F e205, hexagonal ferrite (e.g. barium ferrite), MnB1, etc. are used as magnetic powders (JP-A-52-46803, JP-A-53-67406).
No. 52-78403, No. 55-86103, No. 52-78403, and No. 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 from a sufficiently high coating film. A medium having such a magnetic layer 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. has been done.

This continuous thin film type perpendicular magnetization recording medium has a magnetic recording layer made of an alloy film of cobalt and chromium, as disclosed in Japanese Patent Publication No. 57-17282, and has a particularly high chromium content. states that a Co--Cr alloy film containing 5 to 25% by weight is superior. 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 IEEE, an academic journal published by
Transaction on Magnetism
1982 Vol. 18 No. 6.1116) and cobalt-ruthenium alloy films (for example,
Magnetic recording media using ``Perpendicular Magnetic Recording'' (3) Proceedings of the 8th Tohoku University Research Institute Symposium are known.

Among these, the co-Cr alloy film has been shown to be promising for perpendicular magnetization, but it has been found that it has the following drawbacks.

(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 1 Q Torr or more, and it is necessary to use advanced cleaning treatments for the substrate, low sputtering speed, etc. Such conditions are required, and the control factors for vertical alignment become extremely 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) Since the magnetic layer is hard, cracks are likely to occur when the magnetic layer is provided on a flexible substrate.

(4) The corrosion resistance as a magnetic recording medium is insufficient, and therefore a protective film must be provided on the surface.

(4) (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 determined to obtain a magnetic recording medium that is suitable for high-density perpendicular magnetic recording and has excellent mechanical strength, chemical stability, etc. It was a success.

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 magnetic layer (a) has a thickness of 100 mm and is mainly composed of iron oxide. It should be a continuous magnetic layer of ~5 μm.

(b), the ratio of the residual magnetization (MH) in the in-plane direction of the magnetic layer to the residual magnetization (Mv) in the perpendicular direction to the plane of the magnetic layer (
MV/MH) is 0.5 or more.

The present invention relates to a magnetic recording medium that is precisely equipped with the following configurations.

According to the present invention, since the magnetic layer has iron oxide as its main component, excellent properties unique to oxides (i.e. mechanical strength, chemical stability, etc.) can be obtained, which are necessary for conventional alloy thin films. The surface protective film that was previously used is no longer necessary. As a result, it becomes possible to perform high-density recording by creating a small spacing between the magnetic head and the medium, and it also becomes possible to reduce costs from the viewpoint of materials.

Furthermore, since the residual magnetization ratio (Mv/MH) in the in-plane direction and in the perpendicular direction of the magnetic layer containing iron oxide as the main component is set to 0°5 or more, the magnetic moment of the iron oxide magnetic material is relative to the in-plane direction. It rises in the vertical direction by more than 30 degrees, and has a structure that can fully realize perpendicular magnetization. The residual magnetization amounts Mv and M+-+ can be measured, for example, with a sample vibrating magnetic needle (manufactured by Toei Kogyo Co., Ltd.). That is, MV/MH is 0
．． If it is less than 5, it is difficult to obtain a magnetic moment suitable for perpendicular magnetization.

Furthermore, what is important in the present invention is that the thickness of the magnetic layer is 10
It is set within a specific range of 0 to 5 μm. In the conventional magnetized film, as in the present invention, iron oxide is the main component, and the residual magnetization ratio (Mv /M
In reality, a magnetized film having H) is not expected at all, and no consideration has been given to its thickness range. However, the present inventor discovered for the first time that the thickness of iron oxide-based perpendicularly magnetized films greatly affects the magnetization characteristics, and found that the thickness of iron oxide-based perpendicularly magnetized films greatly affects the magnetization characteristics.
Furthermore, it was confirmed that perpendicular magnetization can be sufficiently achieved when the diameter is 1,000 to 1 μm).

Note that the magnetic layer of the present invention is preferably made of iron oxide having a spinel crystal structure.

The magnetic layer according to the present invention is fundamentally different from conventional coated magnetic layers in that it does not use a binder and is made of iron oxide (e.g. Fe).
30Il, T-Fe205, or a bertolide compound having a non-stoichiometric composition intermediate thereto) itself consists of a continuous thin film. 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.

(7) Oxidized F that exhibits magnetism and is used as a magnetic recording medium
e504, γ-Fe20, these bertholed compounds and their derivatives; and B with a hexagonal crystal structure.
There are a-ferrite, Sr-ferrite, pb-ferrite and their derivatives; and rare earth garnet-type ferrite having a garnet structure. Among the oxides mentioned above, saturation magnetization, which is one of their magnetic properties, is αFeze.
2 Gauss for 5, 350 Gauss for Ba ferrite, Sr ferrite, and PB ferrite, and 140 Gauss for rare earth garnet ferrite. For example, FeO4, which is iron oxide with a spinel structure, has a large value of 480 Gauss. This greatly affects the magnitude of the residual magnetic flux density, that is, the reproduction output when reproducing a recorded signal. Therefore, the magnetic film according to the present invention is preferably an iron oxide having a spinel structure.

However, metals other than iron and oxygen or their (8) 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 amount). , residual magnetization), its crystallinity, and the orientation of the crystal in a specific axis direction! These additive elements or compounds include A7! ,Co%C'o
-Mn, Zn% Co' -Zn, Li
,,Cr,,Ti,,Li-Cr,Mg,Mg-
Ni, Mn-Zn, Ni, N1-A
R,, Ni-Zn, Cu,, Cu-Mn,
, Cu-Zn, V, etc., but it is preferable to use other than rare earth elements.

Further, base materials that can be used in the magnetic recording medium of the present invention include:
Various materials can be used as long as magnetic materials can be attached thereto. For example, plastics such as polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycarbonate, polyimide, polyamide, and polymethyl methacrylate, and ceramics such as glass can 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 applied while the substrate is running. For this purpose, a sputtering method is used 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. Vapor deposition methods etc. can be used.

In either case, the elements constituting the magnetic layer are made to fly,
A continuous thin film is formed on the substrate.

5. Examples The magnetic recording medium of the present invention will be explained in more detail below with reference to the drawings.

As means for depositing the magnetic material used in the present invention on the substrate, there are vacuum evaporation methods (including electric field evaporation and ion blating methods) in which the atoms constituting the magnetic layer are made to fly, sputtering methods, etc. A method using a target sputtering device is preferable.

FIG. 1 shows a facing target sputtering apparatus.

In the drawing, 1 is a vacuum chamber, 2 is an evacuation system consisting of a vacuum pump etc. for evacuating the vacuum chamber I, and 3 is an exhaust system that introduces a predetermined gas into the vacuum chamber 1 and sets the gas pressure to about 10 to 10'Torr. This is a gas introduction system. The target electrodes are configured as opposed target electrodes arranged in parallel and facing each other with a pair of target boulders 4 separating them from each other.

Between these targets is a magnetic field generating means (not shown).
A magnetic field is formed by On the other hand, the substrate 6 on which the thin film is to be formed is placed perpendicularly to the side between the opposing targets by the substrate holder 5.

In the sputtering apparatus configured in this way, a magnetic field is formed in a direction perpendicular to the surfaces of both targets T1 and T2 that face each other in parallel, and this magnetic field generates a magnetic field in the cathode fall area (i.e., between targets '1l and Tz). The γ electrons emitted by the impact of the sputtering gas ions accelerated by the electric field on the target surface in the area between the plasma atmosphere and each of the targets L-'11 and T2 are trapped in the space between the targets, and the Move toward the other target (11). The γ electrons that have moved to the other target surface are reflected at the cathode fall section nearby. Thus, the γ electrons reach the target TI −′r! In between, the reciprocating motion is repeated while being constrained by a 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 α ionization of the atmospheric gas. . Therefore, target 7)'
A high-density plasma is formed in the space between TI and Tz, and the target material is sufficiently sputtered.
The magnetic material will be deposited on the side substrate 6.

Compared to other flying methods, this facing target sputtering device enables film formation at a high deposition rate through high-speed sputtering, and the substrate is not directly exposed to plasma, allowing film formation at low substrate temperatures. This is advantageous for forming a perpendicularly magnetized film. Moreover, since the incident energy (12) of the magnetic film material ejected 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. , it becomes easier to obtain a film with a structure suitable for perpendicular magnetization recording.

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 1 atomic% Co) base
Glass-facing target spacing 100mm Magnetic field in sputtering space 1400e Target shape 100mm diameter disc (5n+
m thickness) Distance between substrate and target end 30n+n+back pressure in vacuum chamber 10Torr Introduced gas Ar+02 Introduced gas pressure 4 x 10Torr Sputter input power 420W In this way, as shown in FIG. A magnetic recording medium having a magnetic layer 10 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 magnetic needle. The characteristics of the obtained magnetic recording medium were as follows.

First, the ratio between the residual magnetization W (MH) in the in-plane direction and the residual magnetization amount (Mv) in the direction perpendicular to the plane is Mv/MH≧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 residual magnetization when MH, M
v.

According to this, it is clear that the former hysteresis curve is smaller than the latter hysteresis curve, and Mv≧0.5M+, 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 measured using an XMA (X-ray microanalyzer; Hitachi model rX-556jKEVEX).
-7000 model), it was found that Fe was the main peak, with a small amount of CO present. Furthermore, in order to investigate the state of iron oxide, measurements were performed using an X-ray diffraction device (1nX-IOR/1 manufactured by JEOL Ltd. using a CuKα tube), and as shown in the table below, the magnetic layer was found to be iron oxide. It was found that the main component is 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.

(10) As a result of further studies on the above-mentioned magnetic layer, it was found that the film structure of the resulting magnetic layer changes depending on its thickness.

That is, if the magnetic layer thickness (film thickness) t is too thin, less than 100, only discontinuous island-like particles N11 are formed on the substrate 6, as shown in FIG. 4(a). I understand. This is completely inappropriate as a perpendicular magnetization film.

For example, in iron oxide, the lattice constants constituting the lattice are as follows.

Lattice constant a (person) F es On 8.390 (A37M
According to card 7-322) T Fe2058.350
(〃4-0755 〃) a-Fezes
5.43 (〃6-0502〃)CoO・Fe
20s 8.33 (〃3-0864〃) Judging from this data, iron oxide scrap with a thickness of less than 100 mm has less than about 12 layers of iron oxide lattice, which is why the above As a result, the film structure becomes discontinuous.

However, in the present invention, the thickness of the iron oxide magnetic layer (16) is suitable for perpendicular magnetization in which the magnetic layers 12 are attached to each other in a direction substantially perpendicular to the surface of the substrate 6 (that is, with the axis of easy magnetization in the perpendicular direction). It was found that a continuous film can be formed.

This is considered to be because the thickness of the magnetic layer is within an appropriate range, so that the particles are regularly stacked in a directional manner during deposition of the magnetic material.

However, if the thickness of the magnetic layer becomes too large, fatal defects will occur, and if the thickness exceeds 5 μm, as shown in Figure 4 (c).
As shown in FIG. 2, after the original columnar small agglomerates 12 are deposited, only small agglomerates 13 with disordered orientation (that is, the axis of easy magnetization is significantly deviated from the vertical direction) are deposited thereon. This is because the magnetic layer is too thick, and particles that attempt to deposit after exceeding the required thickness tend to diffuse laterally (i.e., in the plane of the layer), which causes them to move in the stacking direction of the crystal lattice. This is because disturbance occurs and it becomes virtually impossible to provide the magnetic layer with an axis of easy magnetization in the perpendicular direction.

Next, magnetic recording media having iron oxide magnetic layers of various thicknesses were created by varying the film thickness t, and each magnetic property was measured using a sample vibrating magnetic needle (VSM-33 manufactured by Toa Kogyo Co., Ltd.). The results shown in FIG. 5 were obtained. In addition,
The film thickness was measured using a stylus-type film thickness meter (Kristetsubu) made by Rank Taylor Hobson, but when the film thickness was thin (approximately 100 people), the sensitivity of the magnetic needle was insufficient, so 10 sheets were measured. Measurements were made by stacking several samples. As is clear from FIG. 5, MV/M)I, which indicates the perpendicular magnetization characteristic of a magnetic recording medium, changes depending on the film thickness t of the magnetic layer, and is particularly 0.5 when the thickness is less than 1.6"pm (100 people). It can be seen that even if it is too thick and exceeds 5 μm, it tends to become smaller than 0.5.However, if the film thickness t is 100 μm or more,
If set in the range of 5 μm, Mν/Ms is 0.5 or more,
In particular, when the film thickness t is 200 to 4 μm, it becomes 1.0 or more, and it is understood that it can be used satisfactorily as a perpendicular magnetization film. In this case, it can be seen that if the film thickness t is set to 1000 to 1 μm, a film with the best vertical 101 direct magnetization characteristics can be obtained.

The fact that sufficient perpendicular magnetization characteristics can only be obtained by setting the film thickness range to 100 to 5 μm is a new and useful fact obtained as a result of intensive research by the present inventors.

[Brief explanation of the drawing]

The drawings illustrate the present invention, and FIG. 1 is a schematic sectional view of a facing target sputtering apparatus, FIG. 2 is a sectional view of a magnetic recording medium, FIG. 3 is a hysteresis curve diagram of the magnetic recording medium, and FIG. The figures (a), (b), and (c) are enlarged cross-sectional views of magnetic recording media having magnetic layers with different thicknesses, and Figure 5 shows perpendicular magnetization characteristics (MV/MH
) is a graph showing changes in In addition, in the symbols shown in the drawings, 1--------------------------------------------------------------------------------------------------------- an exhaust system 3, an exhaust system 3 and a gas introduction system 4, 5--- holder 6. --- Substrate 10 --- Magnetic layer 11 --- Discontinuous magnetic particle agglomerates 12 --- Columnar small grain rings 13 --- Small grain agglomerates with disordered orientation T1, T2- ------・Target. Agent Patent attorney Hiroshi Aisaka (1 other person) (zO) 100 people ≦L≦51t1rL

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer is provided on a substrate, wherein the magnetic layer is (a) a continuous magnetic layer containing iron oxide as a main component and having a thickness of 100 to 5 μm. Something. (b) The ratio (MV/MH) of the residual magnetization in the in-plane direction of the magnetic layer (Ml-1) to the residual magnetization (Mv) in the perpendicular direction to the plane of the magnetic layer is 0.5 or more. Something. What is claimed is: 1. A magnetic recording medium comprising: