JPS59148122A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which is suitable for vertical magnetic recording at a high density, has excellent mechanical strength, chemical stability, etc. and has a large reproduced output by forming a magnetic layer of a continuous layer consisting essentially of an iron oxide. 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 high density plasma between the targets T1 and T2, thus forming a continuous magnetic layer 10 on a substrate 6. Fe (contg. 1atom% Co) is used for the target material and Ar+O2 for the gas to be introduced. The magnetic layer having 0.5% 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 <=0.2m surface roughness is formed. The magnetic recording medium which is suitable for vertical magnetic recording at a high density, has excellent mechanical strength, chemical stability and a large reproduced output is thus 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 in the plane are used. occurs, and the playback output decreases significantly. 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 A 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.
This method is considered to have favorable characteristics for high-density recording and is essentially suitable for high-density recording.

By the way, in order to efficiently perform such external 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. medium is known. This coated media includes Co
1Fe504, r Few O3, Co added Fe5
O4, Co-added -Fe@Os, hexagonal ferrite (e.g. barium ferrite), MnB1@ are used as magnetic powders (Japanese Patent Laid-Open No. 52-46803,
No. 53-67406, No. 52-78403, No. 55
-86103, 52-78403, 54-87
202 publications). 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.
Therefore, a medium having a magnetic layer made of a magnetic coating film is unsuitable for perpendicular magnetization recording due to the S/N ratio.

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 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. is Co-Cr with a weight ratio of 5 to 25
The alloy film is said to be superior.

Furthermore, a magnetic recording medium having a magnetic layer formed by adding rhodium of 30% by weight or less 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).
Transaction onM, an academic journal published by EE
agnetism” 1982 Volume 18 A6.11
16 pages) and cobalt-ruthenium alloy films (e.g. 198
A magnetic recording medium using the 18th Tohoku Inutsu Institute Symposium ``Perpendicular Magnetic Recording'' held in March 2016 is 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 10'Torr or more, and the substrate must be subjected to advanced cleaning treatment and a low sputtering speed. etc., 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, the electrical equipment tends to bend 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.

(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 recording medium that is suitable for high-density perpendicular magnetic recording, has excellent mechanical strength and chemical stability, and has a large reproduction output. 4. Structure of the Invention and Its Effects Namely, the present invention provides a magnetic recording medium in which a magnetic layer is provided on a substrate, in which the magnetic layer is (a) oxidized. If it is a continuous magnetic layer mainly composed of iron, then 0 (b), the residual magnetization in the in-plane direction of the magnetic layer (MF[),
The ratio (Mv/MH) to residual magnetization (MY) in the direction perpendicular to the plane of the magnetic layer is 0.5 or more.

The present invention relates to a magnetic recording medium characterized in that the magnetic recording medium is provided on the substrate having a surface roughness of 0.2 μm or less.

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, 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.

Therefore, 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, resulting in a structure that can sufficiently realize perpendicular magnetization.

The magnetization amount MvXMH can be measured, for example, with a sample vibrating magnetometer (manufactured by Toei Kogyo Co., Ltd.). That is, Mv/MH
If is less than 0.5, it is difficult to obtain a magnetic moment suitable for perpendicular magnetization.

Another important point in the present invention is that the magnetic layer has a surface roughness of 0.
．． It is provided on a substrate with a thickness of 2 μm or less.
In the conventional magnetized film, as in the present invention, iron oxide is the main component, and the residual magnetization ratio (Mv /
A magnetized film having MH) is not envisioned at all, and in reality, no consideration has been given to the surface roughness of the substrate on which such a magnetized film is provided in relation to good reproduction characteristics. In this case, the surface roughness of the substrate surface opposite to the magnetic layer is set to 0.3 μm to 3.0 μm.
When the base surface is appropriately roughened, it is effective, for example, to improve the dermotactic properties and winding appearance of the tape.

In the present invention, the substrate on which the iron oxide magnetic layer is provided is 0.2 μm.
Since a material having a surface roughness of less than m is used, the surface of the magnetic layer is appropriately smoothed. In general, in magnetic tapes used for recording/reproducing video signals and magnetic disks for perpendicular magnetic recording, the recording wavelength is 1 μm or less in high-density recording, so the magnetic recording medium used for such purposes is The surface roughness of the magnetic layer must be less than 0.1 μm in order to reduce spacing loss. According to the present invention, as described above, by setting the surface roughness of the substrate within a specific range of 0.2 μm or less, the surface roughness of the magnetic layer can be reduced to 0.1 μm, which is suitable for high-density, high-output perpendicular recording. For the first time, we have achieved the following.

In addition, the above-mentioned "surface roughness" in the present invention is J■506
This corresponds to the maximum height RmaxJ specified in 01.

The magnetic layer according to the present invention is fundamentally different from conventional coated magnetic layers in that it uses iron oxide (e.g. F6) without the use of a binder.
:+04, γ-Fe, IO1, or a bertolide compound having a non-stoichiometric composition intermediate between these) itself consists of a continuous thin film. In this magnetic layer, the sum of both elements iron and oxygen is preferably 50% by weight or more of the magnetic layer, and more preferably 70% by weight or more. 1. The ratio of iron and oxygen is preferably 1 to 3, the number of oxygen atoms minus 7, and the number of iron atoms = 1 to 3. Even better, the ratio of iron to oxygen is 1 to 3. Iron is suitable.

When the iron oxide has a spinel crystal structure,
The amount of saturation magnetization is large, and the residual magnetic flux density is large during recording (Ft number reproduction), resulting in extremely good reproduction sensitivity.

In general, iron oxides exhibiting magnetism include α-Fears, which has rhombohedral parasitic ferromagnetism; Fe5Q4, I Fe2es, or their bertolide compounds, which have a spinel structure and exhibit ferrimagnetism; Ba, which is a hexagonal oxide. ferrite, Sr ferrite, Pb ferrite or derivatives thereof; rare earth garnet type ferrite with garnet structure. Among these iron oxides, the saturation magnetization, which is one of the important magnetic properties, is 2 for α-Fe-0*.
．． OGauss, Ba ferrite, Sr ferrite, and Pb ferrite have a maximum saturation magnetization of about 380 Gauss, while spinel ferrite has a saturation magnetization of 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, since it provides a sufficient residual magnetic flux density and good reproduction sensitivity. On the other hand, there are Ba ferrite and Sr ferrite that exhibit a saturation magnetic flux density similar to that of 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° in a sputtering device, which will be described later. C and high? 1. This limits the type of substrate (for example, plastic substrates with poor heat resistance cannot be used).
The spinel type iron oxide of the present invention can be formed into a film at a low temperature of room temperature to 300'C, and is not limited by the substrate material. However, the magnetic layer may contain metals other than iron and oxygen or their oxides,
Alternatively, non-metals, semimetals, or their compounds can be added to improve the magnetic properties of the magnetic layer (the amount of coercive saturation magnetization and the amount of residual magnetization), its crystallinity, and the orientation of the crystal in a specific axis direction. It is possible to improve the Examples of such additive elements or compounds include AI, Co, Co-Mn
XZn, Co-Zn, LiX0rX71, Li-
CrXMg.

Mg-Ni, Mn-Zn, Ni, Ni-A4XN
i-Zn, Cu.

Examples include Cu-ΔInXCu Zns, V, etc., but other elements and compounds may also be used.

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 they can be coated with magnetic materials and have a surface roughness of 0.2 μm or less. For example, as a substrate exhibiting desirable surface smoothness, a substrate made of plastics such as polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycarbonate, polyimide, polyamide, polymethyl methacrylate, ceramics such as glass, etc. can be used. 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 applied while the substrate is running. For this purpose, a magnetic material target is sputtered in a processing chamber connected to an evacuation system such as a vacuum pump, or a sputtering method is used in which the material is evaporated from a magnetic material evaporation source and deposited on the substrate. , vapor deposition methods are applicable. In either case, the elements constituting the magnetic layer are blown away to form a continuous thin film 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 a means for depositing the magnetic material used in the present invention on the substrate, a vacuum evaporation method ('d
Including l-field deposition and ion blating methods. ), sputtering methods, etc. Among these methods, a method using a facing target sputtering device is preferable.

FIG. 1 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 maintain a gas pressure of about 10-1 to 10'Torr. This is the gas introduction system to be set.

The target electrode is configured as a facing target electrode in which a pair of target electrodes Ts and Tz are spaced apart from each other by a target holder 4 and arranged to face 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 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 the two targets (Tt, -Tt) facing each other in parallel, and this magnetic field causes the cathode descending part (i.e., the target layer) T, -T, The γ electrons emitted by the collision of the sputtering gas ions accelerated by the electric field with the target surface in the region between the plasma atmosphere generated in between and each target T and T2 are trapped in the space between the targets. , move toward the other opposing 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 electron is
The reciprocating motion is repeated between TxTz while being constrained by the magnetic field. During the reciprocating motion of B, 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. let Therefore,
A high-density plasma is formed in the space between the targets TITs, and the target material is sufficiently sputtered and deposited on the lateral substrate 6 as a magnetic material.

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. Furthermore, the incident energy of the magnetic film material emitted onto the substrate by the facing target sputtering device is lower than that of a normal sputtering device, so the material is easily deposited directionally in the desired direction, and the 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 conditions for its creation were as follows.

Target material Iron (contains 1 atom of Co) base
Glass-facing target spacing 100fi Magnetic field in sputtering space 1000e Target shape 100-diameter disk (5ml thickness)
Distance between substrate and target end 30 points Back pressure in vacuum chamber 10' Torr Introduced gas Ar
10 Ox 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 film 6 was obtained as shown in FIG. 2. This medium The characteristics of the magnetic layer were evaluated using an X-ray microanalyzer (XMA).The characteristics of the obtained magnetic recording medium were as follows.

First, the ratio of the residual magnetization in the in-plane direction (Nbl) to the residual magnetization in the perpendicular direction (MY) is My/MH≧
It was 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 are obtained, respectively, but when the applied magnetic field is zero, The amount of magnetization at each time is M■
, Mv. According to this, the former hysteresis curve is smaller than the latter hysteresis curve, and Mv≧0.
It is clear that the magnetic field is 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 the magnetic recording medium with XMA (X-ray microanalyzer: Hitachi rX-5ssj
-7000 model), it was found that Fe was the main peak and a small amount of Co was included. Furthermore, in order to examine the state of iron oxide, an X-ray diffraction device (JEOL r JDX-1 (IRA J: using a CuKα tube) was used.
As shown in the table below, it was found that the magnetic layer was mainly composed of iron oxide. Moreover, it was observed using an electron microscope that this magnetic layer had an ordered structure in the direction perpendicular to the in-plane direction.

In addition, before forming a film by the above sputtering method, the surface of the substrate is cleaned by bombarding it with Ar+ in the same sputtering device, or it is subjected to baking, or the surface is treated by applying high frequency. is desirable.

For the magnetic recording medium obtained as described above, disks having various surface roughnesses were used as the substrate 6, and Fe5Oa for perpendicular magnetization with a thickness of 5000 A was deposited on these substrates.
A film (however, the coercive force (He) was 1000Qe) was formed respectively. These magnetic recording media (magnetic disks) were installed in a known recording/reproducing device, and an effective head gap of 0.3μ was achieved.
Recording and reproduction were performed using a ring-shaped head with a rack width of 100 μm.

As a result, results as shown in FIG. 4 were obtained for each disk. That is, the reproducing voltage (vertical axis) changes with respect to the linear recording density (horizontal axis), but if the surface roughness of the substrate is outside the range of the present invention, for example, Rmax = 0.3 μm, As shown by the broken line, the reproduction output is particularly low in the high range, but it is within the scope of the present invention (for example, Rmax =
0.15 μm, 0.2 μm), the reproduction output was significantly improved as shown by the dashed line and the solid line, and it was found that it is extremely suitable for high-density recording.

[Brief explanation of drawings]

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 figure is a graph showing a comparison of data on the relationship between recording density and reproduction output obtained when the surface texture of the substrate is changed. 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.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium in which a magnetic layer is provided on a substrate, wherein the magnetic layer consists of (a) a continuous magnetic layer containing iron oxide as a main component; (b), residual magnetization (Myi) in the in-plane direction of the magnetic layer,
The ratio of the residual magnetization (Mv) in the direction perpendicular to the surface of the magnetic layer (Mv / Ml () is 0.5 or more.) and the surface roughness is 0.2 μm or less. A magnetic recording medium, characterized in that it is provided on the base.