JPH04229413A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain higher coercive force than coercive force dependent on the inclination of prismatic grains to a substrate or higher saturation magnetic flux density in case of the conventional coercive force by laminating thin ferromagnetic metal films on the substrate with a nonmagnetic thin film of a prescribed thickness in-between. CONSTITUTION:Thin ferromagnetic metal films each consisting of prismatic grains formed by diagonal vapor deposition are laminated on a substrate with a nonmagnetic thin film in-between to obtain a magnetic recording medium. The growth directions of the prismatic grains of the adjacent films intersect each other with a normal of the substrate in-between and the angle (theta) between the growth direction of the prismatic grains of each of the films and the principal face of the substrate is larger than the angle (E) between the principal face of the substrate and the direction of the axis of easy magnetization after correction of a demagnetizing field.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-plane recording type magnetic recording medium having, as a magnetic layer, a ferromagnetic metal thin film made of columnar crystal grains formed by an oblique evaporation method.

0002

[Prior Art] In recent years, magnetic recording media have become increasingly dense, and in particular, magnetic recording media that use ferromagnetic metal thin films that are mainly composed of Co and added with Ni, etc. have a high saturation magnetic flux density and a low coercive force. Because it is expensive, it is being actively researched.

[0003] This type of magnetic recording medium is manufactured by various methods, but a particularly excellent method is to laminate two or more ferromagnetic metal thin films on a nonmagnetic substrate by oblique vapor deposition to form a multilayer structure. It is proposed that. In the oblique deposition method, each layer of ferromagnetic metal thin film is produced by directing ferromagnetic metal vapor onto the surface of a non-magnetic substrate at a specific angle using a vapor phase method such as evaporation, which causes columnar crystal grains of ferromagnetic metal to separate from other layers. It is formed by growing a ferromagnetic metal thin film in a specific direction intersecting the growth direction of columnar crystal grains (Japanese Patent Publication No. 56-26891, 56-
42055, 63-21254 and 60-37528
, Japanese Patent Publication No. 54-603, 54-147010, 56-9
4520, 57-3233, 57-30228, 57-
13519, 57-141027, 57-41028,
57-141029, 57-143730, 57-14
3731, 57-147129, 58-14324, 5
8-50628, 60-76025, 61-11033
3, 61-187122, 63-10315, 63-1
0315, 63-13117, 63-14317, 63
-14320 and 63-39127, etc.).

[0004] When forming a ferromagnetic metal thin film on an oblique deposition type magnetic recording medium, a non-magnetic substrate is placed on the surface of a rotating cylindrical cooling drum and is transported while an electron beam or the like is applied to a stationary ferromagnetic metal source. Vapor deposition is performed by irradiating the

[0005] At this time, the angle between the direction in which the ferromagnetic metal is incident and the normal to the surface of the nonmagnetic substrate is called the angle of incidence, and the deposition is normally performed so that the angle of incidence gradually decreases from the start to the end of the deposition.

[0006] The deposition rate is the lowest at the start of deposition when the angle of incidence is the largest, and increases rapidly as the angle of incidence increases. Therefore, the columnar crystal grains in the ferromagnetic metal thin film are nearly parallel to the nonmagnetic substrate surface on the nonmagnetic substrate side, and as they move away from the nonmagnetic substrate surface, they rise rapidly and grow in an arc shape.

The direction of the easy axis of magnetization of such a ferromagnetic metal thin film depends on the inclination of the columnar crystal grains. Since the maximum angle of incidence is usually 90°, the inclination of the columnar crystal grains depends on the minimum angle of incidence.

[0008] When the minimum incident angle is reduced, the inclination of the columnar crystal grains with respect to the normal to the substrate becomes smaller. That is, the columnar crystal grains stand up against the substrate. In this state, the axis of easy magnetization also stands in relation to the substrate, so
The coercive force in the in-plane direction of the ferromagnetic metal thin film decreases.

On the other hand, when the minimum incident angle is increased, the columnar crystal grains lie flat against the substrate, and the axis of easy magnetization also lies flat against the substrate, so that the in-plane direction of the ferromagnetic metal thin film is Coercive force increases. However, in this case, the saturation magnetic flux density becomes small.

[0010] Even in a magnetic layer formed by laminating two or more ferromagnetic metal thin films, the relationship between the inclination of columnar crystal grains, coercive force, and saturation magnetic flux density is the same as above.

[0011]

SUMMARY OF THE INVENTION The present invention was made in view of the above circumstances, and it is an object of the present invention to provide an obliquely deposited magnetic recording medium having a high saturation magnetic flux density and a high coercive force.

0012

[Means for Solving the Problems] Such objects are achieved by the present invention as described in (1) to (8) below.

(1) A magnetic layer is provided on the substrate, and this magnetic layer is formed between two or more layers of ferromagnetic metal thin films made of columnar crystal grains formed by an oblique evaporation method and adjacent ferromagnetic metal thin films. It has a laminated structure with a non-magnetic thin film that exists in
The ferromagnetic metal thin film is composed of a first group and a second group, and the average growth direction of the columnar crystal grains of the ferromagnetic metal thin film belonging to the first group and the ferromagnetic metal thin film belonging to the second group are The average growth direction of the columnar crystal grains of the magnetic metal thin film intersects with the normal line of the substrate, and the ferromagnetic metal thin film belonging to the first group and the ferromagnetic metal thin film belonging to the second group A ferromagnetic metal thin film belonging to the second group and a ferromagnetic metal thin film belonging to the first group are present on at least one side, and each ferromagnetic metal thin film has an average growth direction of columnar crystal grains. Let the angle between the main surface of the substrate be θ (0<θ<90°), and the angle between the direction of the axis of easy magnetization after demagnetizing field correction and the main surface of the substrate be E (0<E<9
0°), a magnetic recording medium characterized in that θ>E.

(2) θ/E= for each ferromagnetic metal thin film
The magnetic recording medium according to (1) above, in which 1.4 to 5 are satisfied.

(3) The above (1), wherein the nonmagnetic thin film is mainly composed of an oxide of an element contained in the ferromagnetic metal thin film.
Or the magnetic recording medium according to (2).

(4) The magnetic recording medium according to any one of (1) to (3) above, wherein the nonmagnetic thin film contains Co oxide as a main component.

(5) The method according to any one of (1) to (4) above, wherein the thickness of the non-magnetic thin film is 0.12 to 0.5 times the average thickness of the ferromagnetic metal thin film. magnetic recording medium.

(6) The magnetic recording medium according to any one of (1) to (5) above, wherein the ferromagnetic metal thin film contains Co as a main component.

(7) Fine particles are disposed on the surface of the substrate, and the center line average roughness Ra of the substrate after disposing the fine particles is 40A or less, and the chain ratio of the fine particles is 70. % or less, the magnetic recording medium according to any one of (1) to (6) above.

(8) The in-plane coercive force of the magnetic layer is 1
200 Oe or more, and the residual magnetic flux density is 400
The magnetic recording medium according to any one of (1) to (7) above, which has a resistance of 0 G or more.

[0021]

In the magnetic recording medium of the present invention, two or more ferromagnetic metal thin films made of columnar crystal grains formed by oblique vapor deposition are laminated with a nonmagnetic thin film interposed therebetween.

In a single-layer ferromagnetic metal thin film, the above θ and E are approximately equal, but in the present invention, by laminating ferromagnetic metal thin films through a nonmagnetic thin film of a predetermined thickness, the average of columnar crystal grains is Interaction occurs between the ferromagnetic metal thin films whose growth directions intersect with each other across the normal line of the substrate, so that θ>E can be satisfied. That is, the direction of the easy axis of magnetization after demagnetizing field correction is usually the same as the average growth direction of columnar crystal grains, but according to the present invention, the direction of the easy axis of magnetization can be brought closer to parallel to the substrate. Note that the above-mentioned interaction mainly occurs between two adjacent ferromagnetic metal thin films.

Therefore, according to the present invention, a coercive force higher than the coercive force depending on the inclination of the columnar crystal grains with respect to the substrate can be obtained. Note that the coercive force in this case is the coercive force in the in-plane direction of the magnetic layer.

[0024] Furthermore, if the inclination of the columnar crystal grains with respect to the substrate is large, a high saturation magnetic flux density can be obtained, so a higher saturation magnetic flux density can be obtained while maintaining the same coercive force as the conventional one.

As described above, by controlling the thickness of the nonmagnetic layer and the inclination of the columnar crystal grains, a value of 1200 Oe or more can be obtained as a coercive force in the in-plane direction, and a value of 4000 G or more as a residual magnetic flux density can be obtained. can get.

Further, in the present invention, if a substrate on which fine particles are provided is used, the friction of the magnetic layer is reduced and the durability is improved. If the centerline average roughness Ra of the substrate after disposing fine particles is 40A or less and the chain ratio of fine particles is 70% or less, the columnar crystal grains will grow homogeneously, so a high coercive force can be obtained. It will be done.

[0027]

[Specific Configuration] The specific configuration of the present invention will be explained in detail below.

The magnetic recording medium of the present invention has a magnetic layer on a substrate. The magnetic layer has a laminated structure of a ferromagnetic metal thin film made of columnar crystal grains formed by oblique vapor deposition and a nonmagnetic thin film existing between adjacent ferromagnetic metal thin films.

The ferromagnetic metal thin film in the magnetic layer is composed of a first group consisting of one or more layers of ferromagnetic metal thin film and a second group consisting of one or more layer of ferromagnetic metal thin film. The average growth direction of the columnar crystal grains of the ferromagnetic metal thin film belonging to the first group and the average growth direction of the columnar crystal grains of the ferromagnetic metal thin film belonging to the second group intersect with each other across the normal to the substrate. ing. A magnetic layer having such a structure can be easily obtained by reversing the running direction of the substrate between the first group and the second group when depositing a ferromagnetic metal thin film by the oblique evaporation method described later. can.

In the present invention, at least one side of the ferromagnetic metal thin film belonging to the first group and the ferromagnetic metal thin film belonging to the second group are provided with a ferromagnetic metal thin film belonging to the second group and a ferromagnetic metal thin film belonging to the second group, respectively. There are ferromagnetic metal thin films belonging to the first group. That is, three ferromagnetic metal thin films in which the average growth direction of columnar crystal grains is in the same direction do not exist in succession.

For each ferromagnetic metal thin film, the angle between the average growth direction of columnar crystal grains and the main surface of the substrate is θ, and the angle between the direction of the easy axis of magnetization after demagnetizing field correction and the main surface of the substrate is When E, θ>E, that is, θ/E>1, preferably θ/E=1.4 to 5, more preferably 1.5 to 5. However, 0<θ<90°, 0<E<
It is 90°.

In the present invention, θ and E have such a relationship due to the interaction between two ferromagnetic metal thin films whose average growth directions of columnar crystal grains intersect with each other across the normal to the main surface of the substrate. Therefore, the coercive force in the in-plane direction of the magnetic layer can be improved.

The angle θ between the average growth direction of the columnar crystal grains and the main surface of the substrate is measured as follows.

First, a magnetic recording medium is cut along a plane that includes the growth direction of columnar crystal grains (usually a plane that is perpendicular to the main surface of the medium and includes the running direction of the magnetic head). In the cross section, the cross section of the columnar crystal grains constituting each ferromagnetic metal thin film appears in an arc shape. The angle between the side surface of the columnar crystal grains that appeared in this cross section (the boundary line between adjacent columnar crystal grains) and the main surface of the substrate was measured for at least 100 columnar crystal grains for each ferromagnetic metal thin film, and Find their average value in the metal thin film. Each of these average values is defined as the angle θ between the average growth direction of columnar crystal grains in each ferromagnetic metal thin film and the main surface of the substrate. Note that the measurement position of θ is the midpoint in the thickness direction of the ferromagnetic metal thin film.

[0035] θ depends on the direction of incidence of the ferromagnetic metal in the oblique evaporation method, and particularly on the minimum incidence angle θmin.

In the present invention, the range of θ is not particularly limited. That is, in the present invention, no matter what θ, θ and E
The effect is realized if and satisfies the above relationship. Therefore, the required in-plane coercive force and saturation magnetic flux density,
Alternatively, an appropriate θ may be selected depending on the position of the ferromagnetic metal thin film within the magnetic layer, etc., but in order to obtain high coercive force and high residual magnetic flux density, θ = 40 to 80°, especially θ
=50 to 70° is preferable.

Furthermore, the angle E between the direction of the axis of easy magnetization after demagnetizing field correction and the main surface of the substrate is determined as follows.

The easy axis direction of the entire magnetic layer can be determined by measuring the out-of-plane angle dependence of the squareness ratio of the magnetic layer.

Specifically, in the plane that is the cutting plane for θ measurement, the angle with the main surface of the substrate is from 0° to 180°.
The squareness ratio is measured in a range up to 100°, and a graph of the out-of-plane angle dependence of the squareness ratio is created by taking the angle between the main surface of the substrate and the measurement direction on the horizontal axis and the squareness ratio on the vertical axis. The measurement may be performed using a vibrating sample magnetometer (VSM) or the like.

From the graph of the out-of-plane angle dependence of the entire magnetic layer thus prepared, the direction of the easy axis of magnetization of each ferromagnetic metal thin film constituting the magnetic layer is determined as follows.

First, it is assumed that a magnetic layer is formed by laminating ferromagnetic metal thin films with the same thickness as the magnetic layer to be measured, and this magnetic layer is used as a magnetic layer for simulation. For this magnetic layer for simulation, a graph of the out-of-plane angle dependence of the squareness ratio is created by simulation.

In such a magnetic layer for simulation, the simulation is repeated while changing the axis of easy magnetization of the ferromagnetic metal thin film in predetermined steps, and a graph of the out-of-plane angle dependence of the squareness ratio is created. Note that the easy axis direction of magnetization is changed for all ferromagnetic metal thin films from the bottom layer to the top layer, and the magnetic layer composed of laminated ferromagnetic metal thin films whose easy axis directions have been changed respectively. , perform a simulation.

[0043] Among the graphs obtained by these simulations, one is selected that almost coincides with the out-of-plane angle dependence graph of the squareness ratio obtained from the above-mentioned actual measured values of the magnetic layer. The direction of the easy axis of magnetization of each ferromagnetic metal thin film of the simulation magnetic layer selected at this time matches the direction of the easy axis of magnetization of each ferromagnetic metal thin film of the actual magnetic layer. If the demagnetizing field correction described later is applied to the measured graph and the simulated graph, then the angle between the direction of the axis of easy magnetization of each ferromagnetic metal thin film in the simulation magnetic layer and the main surface of the substrate is
This corresponds to E of each ferromagnetic metal thin film in the actual magnetic layer.

Note that the out-of-plane angle dependence of the squareness ratio is affected by the demagnetizing field within the magnetic layer. The effect of the demagnetizing field becomes larger as the recording wavelength becomes shorter. When used as a magnetic recording medium, the recording wavelength is extremely short and is hardly affected by the demagnetizing field; however, when measuring the above-mentioned out-of-plane angle dependence of the squareness ratio, the wavelength is relatively long, so the demagnetizing field does not affect the recording wavelength. becomes a problem.

A demagnetizing field is generated in the thickness direction of the ferromagnetic metal thin film, and its magnitude Hd is Bm sin2θ. Therefore, the direction of the easy axis of magnetization determined by measurement is the direction of the composite vector of the magnetization vector in the actual easy axis direction and the demagnetizing field vector, and is a direction closer to parallel to the main surface of the substrate than the actual easy axis of magnetization. Become. The actual direction of the axis of easy magnetization can be found using this relationship.

Such correction of the demagnetizing field may be performed before creating the out-of-plane angle dependence graph of the squareness ratio, or after comparison with the graph obtained by the above simulation.

The nonmagnetic thin film existing between the ferromagnetic metal thin films has the function of adjusting the magnetic interaction between the ferromagnetic metal thin films on both sides.

The thickness of the nonmagnetic thin film is preferably 0.12 to 0.5 times the average thickness of each ferromagnetic metal thin film. When the thickness exceeds the above range, there is almost no interaction between the ferromagnetic metal thin films on both sides, and θ/E becomes significantly small. Moreover, if the thickness is less than the above range, an interaction other than the above interaction will occur between the ferromagnetic metal thin films on both sides, and θ/E will become smaller.

The nonmagnetic thin film preferably has an oxide of an element contained in the ferromagnetic metal thin film as a main component. Such a non-magnetic thin film can be formed, for example, by introducing oxygen gas into the film-forming atmosphere when forming a ferromagnetic metal thin film by the oblique evaporation method described below, so it can be formed with high productivity. You can get sex. Furthermore, by introducing oxygen gas into the film-forming atmosphere, a small amount of oxygen is taken into the non-magnetic thin film, which also has the effect of improving the coercive force.

Note that in the nonmagnetic thin film containing an oxide formed by such a method, the oxygen concentration gradually changes near the interface with the ferromagnetic metal thin film, but in the present invention, the oxygen concentration of the nonmagnetic thin film changes gradually. The thickness is defined as below. That is, Mave is the average value of the oxygen concentration at the midpoint in the thickness direction of the two ferromagnetic metal thin films existing on both sides of the nonmagnetic thin film,
If the maximum oxygen concentration of the non-magnetic thin film is Nmax, then (Nmax+Mave)/including the maximum oxygen concentration point of the non-magnetic thin film
The thickness of the region having an oxygen concentration of 2 or more is defined as the thickness of the nonmagnetic thin film.

Although there is no particular restriction on the value of the maximum oxygen concentration Nmax of the nonmagnetic thin film, in order to adjust the interaction between the ferromagnetic metal thin films and obtain the above-mentioned θ/E, the maximum oxygen concentration Nmax must be set. It is preferably 20% or more.

Note that the oxygen concentration in the nonmagnetic thin film can be measured by performing elemental analysis by Auger spectroscopy or the like while etching the magnetic layer.

The non-magnetic thin film in the present invention is not limited to a thin film mainly composed of oxides as described above, but may also be a thin film mainly composed of various non-magnetic compounds other than oxides or non-magnetic metals. Good too. Various compounds other than oxides are also preferably compounds of elements contained in the ferromagnetic metal thin film. Further, the thickness of the nonmagnetic thin film in this case may be determined by measuring the concentration of nitrogen or carbon in the magnetic layer, and in accordance with the thickness measurement of the above-mentioned nonmagnetic thin film containing an oxide as a main component.

[0054] The nonmagnetic thin film may exist not only between adjacent ferromagnetic metal thin films, but also between the substrate and the bottom layer of the ferromagnetic metal thin film, or on the top layer of the ferromagnetic metal thin film. .

There is no particular limit to the thickness of the magnetic layer made of the ferromagnetic metal thin film and nonmagnetic thin film as described above, but it is usually 1.
It is preferable that it is 000A or more. This makes it possible to sufficiently increase the output in the low frequency range of about 0.75 MHz, for example.

Further, the thickness of each ferromagnetic metal thin film is approximately 20
It is preferable that it is 0-1500A. If the thickness of the top layer becomes thinner than 200 Å, it becomes impossible to sufficiently record a high frequency signal of, for example, about 7.0 MHz, and the output decreases. On the other hand, if it becomes thicker than 1500A, noise increases and the signal-to-noise ratio decreases.

[0057] There is no particular limit to the number of laminated ferromagnetic metal thin films, but a structure of two, three, or four or more layers may be appropriately selected in consideration of magnetic properties and productivity.

In the present invention, the ferromagnetic metal thin film is preferably a Co-based alloy containing Co as a main component, and the Co content in the ferromagnetic metal thin film is preferably 60 atomic % or more. Co-based alloys include Co and Ni.
or an alloy containing Co, Ni, and Cr as main components is preferable. The content of each element other than Co may be appropriately selected depending on the required magnetic properties and corrosion resistance.

Each ferromagnetic metal thin film is formed by an oblique vapor deposition method. There are no particular restrictions on the oblique evaporation apparatus and method, and ordinary ones may be used.

In the oblique vapor deposition method, for example, a long film-like nonmagnetic substrate unwound from a supply roll is fed along the surface of a rotating cooling drum while oblique vapor deposition is performed from one or more stationary metal sources. It is wound onto a take-up roll. In this case, the incident angle is the maximum incident angle θm at the initial stage of vapor deposition.
The angle of incidence changes continuously from ax to the final minimum incident angle θmin, and columnar crystal grains of ferromagnetic metal containing Co as a main component are grown in an arc shape and aligned on the surface of the nonmagnetic substrate.

[0061] When the magnetic layer has a multilayer structure, this step is repeated.

When forming a two-layer ferromagnetic metal thin film in which the direction of incidence of the ferromagnetic metal crosses the normal line of the nonmagnetic substrate, oblique deposition is performed with the running direction of the nonmagnetic substrate reversed. All you have to do is

There are no particular restrictions on the method of forming a nonmagnetic thin film, but if the deposition is carried out by introducing oxygen gas into the film forming atmosphere, a nonmagnetic thin film whose main component is the oxide of the constituent elements of the ferromagnetic metal thin film can be formed. can be formed extremely easily.

In addition, a nonmagnetic thin film containing oxide as a main component can also be formed by a method in which the surface of a ferromagnetic metal thin film is treated with oxygen gas or its plasma.

Furthermore, by alternately depositing ferromagnetic metal thin films and nonmagnetic metal thin films, Al, Cr, Ag
, Au, Pt, Ti, W, etc. as main components can also be formed.

The material of the substrate used in the present invention is not particularly limited as long as it is nonmagnetic, and various films that can withstand the heat during deposition of a ferromagnetic metal thin film, such as polyethylene terephthalate, can be used. Also, JP-A-63-1031
Various materials described in Publication No. 5 can be used.

[0067] The surface of the substrate used in the present invention is preferably provided with minute protrusions. Since the magnetic layer is a vapor deposited film and is extremely thin, the properties of the substrate surface directly appear on the magnetic layer surface. Therefore, if minute protrusions are provided on the surface of the substrate, minute protrusions can also appear on the surface of the magnetic layer. The protrusions on the surface of the magnetic layer reduce the friction of the magnetic layer, improve running properties when formed into a tape, and increase the durability of the medium.

The properties and formation method of the minute protrusions on the surface of the substrate are not particularly limited, but the arrangement pattern of the protrusions and the surface roughness of the substrate after the protrusions are formed affect the magnetic properties of the magnetic layer, especially the coercive force. In the present invention, it is preferable to provide the protrusions by disposing fine particles on the surface of the substrate.

The fine particles used are preferably granular, particularly approximately spherical, such as SiO2, Al2
O3, MgO, ZnO, MgCO3, CaCO3, Ca
Inorganic particles containing one or more of oxides such as SO4, BaSO4, TiO2, sulfates, carbonates, etc., oxides or acid salts of metals such as Si, Al, Mg, Ca, Ba, Zn, Mn, etc., or Spherical particles of one or more organic compounds such as polystyrene, polyester, polyamide, polyethylene, etc. are preferred. These fine particles may or may not have magnetism.

[0070] The average particle diameter of the fine particles is 100 to 1000.
A, particularly preferably 300 to 600A. If the average particle diameter is less than the above range, the friction reduction effect will be small;
The durability improvement effect is also insufficient. In addition, if the average particle diameter exceeds the above range, the surface roughness of the magnetic layer increases, making it difficult to achieve the center line average roughness Ra described later, resulting in a decrease in coercive force and insufficient high frequency characteristics. .

[0071] The arrangement density of fine particles is 1/mm2.
The number is preferably 00,000 to 100 million, particularly 1 million to 70 million. If the arrangement density is too low, the effect of providing fine particles will be insufficient. Moreover, if the arrangement density is too high, no improvement in the effect will be observed, and it will be difficult to achieve the chain ratio described below.

It is preferable that the fine particles are distributed as uniformly as possible. When particles aggregate or come extremely close to each other, they behave as apparently large particles (secondary particles), which is undesirable. In this specification, the degree of proximity between fine particles is defined by the chain ratio. That is, when the diameter of the particles disposed on the surface of the substrate is R, and the distance between adjacent particles is d, the chain ratio = (d<
Number of particles satisfying R per unit area) x 100/
It is defined as (number of particles per unit area) (unit: %). In addition, the average particle diameter is adopted as R, and the interparticle distance d
The number of particles is measured using an electron microscope photograph.

[0073] In the present invention, such a chain ratio is 70%.
Below, it is particularly preferable that it is 0 to 60%. If the chain ratio exceeds the above range, the fine particles behave as secondary particles, making it difficult for the columnar crystal grains to grow in the same direction, resulting in a decrease in coercive force. Further, after the magnetic layer is formed, the diameter and height of the protrusions appearing on the surface of the magnetic layer become significantly large, the surface properties of the magnetic layer deteriorate, and the electromagnetic conversion characteristics deteriorate due to spacing loss.

Centerline average roughness R of the substrate after fine particles are disposed
It is preferable that a is 40A or less, particularly 30A or less. When Ra exceeds the above range, the growth directions of columnar crystal grains become difficult to align, and the coercive force tends to decrease. Note that if Ra is too low, the friction reduction effect will be insufficient and the durability will be low, so it is preferable that Ra is 10A or more.

The method for disposing the fine particles on the surface of the substrate is not particularly limited, but for example, a method in which fine particles are dispersed in a thin binder made by dissolving a base resin in a solvent is coated on the substrate, or a method in which such a binder is applied A method of applying fine particles on top of the coating is preferably used.

Preferably, various known top coat layers are provided on the magnetic layer of the magnetic recording medium of the present invention in order to protect the magnetic layer and improve corrosion resistance. Furthermore, in order to ensure runnability when formed into a tape, it is preferable that various known back coat layers be provided on the side of the nonmagnetic substrate opposite to the magnetic layer.

The magnetic recording medium of the present invention is suitable for various kinds of magnetic recording in the in-plane direction of the magnetic layer, and since the coercive force in the in-plane direction of the magnetic layer can be improved, high-density recording is possible.

[0078]

EXAMPLES Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in more detail.

[Example 1] 0.15% by weight of SiO2 (average particle size 300A) as fine particles, 0.2% by weight of methyl cellulose as a binder, and a silane coupling agent [N-β(aminoethyl)-γaminopropyl] 0.02% by weight of methyldimethoxysilane was sufficiently mixed and dispersed in a formulation containing water as the balance solvent, and the resulting suspension was poured into a 7 μm thick polyethylene terephthalate (P
ET) was applied onto the surface of the substrate and dried.

[0080] The arrangement density of fine particles after drying is 10 million particles/
mm2, the chain ratio was 50%, and the Ra of the substrate surface was 30A.

Next, a ferromagnetic metal thin film was deposited on the surface of the substrate.

The substrate is let out from the connecting roll and moved along the circumferential surface of a rotating cylindrical cooling drum, and a ferromagnetic metal is deposited obliquely to form a ferromagnetic metal thin film, which is then wound onto a take-up roll. Ta.

Next, using this winding roll as a supply roll, a ferromagnetic metal is obliquely deposited in the direction of incidence that intersects the direction of incidence during the above-mentioned oblique deposition across the normal direction of the substrate surface, thereby forming a magnetic recording medium sample. Created.

[0084] When forming the upper and lower ferromagnetic metal thin films, a mixed gas of Ar gas and O2 gas was flowed into the vacuum chamber, and the pressure inside the vacuum chamber was maintained at 10-4 Torr. Further, the mixed gas was flowed so as to be blown onto the substrate at the portion to be vapor-deposited near the minimum incident angle.

A plurality of samples were prepared by changing the O2 gas concentration in the mixed gas.

A ferromagnetic metal having a composition of 80 atomic % Co and 20 atomic % Ni was used to form the upper and lower layers of each sample.

[0087] Each sample thus formed was
A nonmagnetic thin film made of an oxide was provided between the lower ferromagnetic metal thin film and the upper ferromagnetic metal thin film.

The ratio of the thickness of the nonmagnetic thin film to the ferromagnetic metal thin film (nonmagnetic thin film/ferromagnetic metal thin film) of each sample is shown in Table 1 below. The thickness of the nonmagnetic thin film was determined by measuring the oxygen concentration distribution in the magnetic layer by Auger spectroscopy, and based on the results, by the method described above. Note that the thickness of the ferromagnetic metal thin film was 1000A for both the lower layer and the upper layer.

Regarding each ferromagnetic metal thin film of each sample,
Angle θ between the average growth direction of columnar crystal grains and the main surface of the substrate
was measured by the method described above. The number of columnar crystal particles measured was 100. The results are shown in Table 1.

For each sample, the above-mentioned out-of-plane angle dependence graph of the squareness ratio was created. VSM was used for the measurement. Then, for the simulation magnetic layer as described above, a graph of the out-of-plane angle dependence of the squareness ratio was created by changing the easy axis direction of magnetization of each ferromagnetic metal thin film. These graphs were compared with the out-of-plane angle dependence graph of the squareness ratio of each sample, and the angle E between the easy axis of magnetization and the main surface of the substrate was determined for each ferromagnetic metal thin film of each sample. The results are shown in Table 1.

For each sample, the coercive force Hc in the in-plane direction of the magnetic layer and the residual magnetic flux density Br were measured. The results are shown in Table 1.

[0092]

[Table 1]

From the results shown in Table 1, the effects of the present invention are clear.

[0094] When applying the above compound to the surface of the substrate, the coating conditions such as the amount of coating were changed to change the chain ratio of fine particles to 80% and the Ra of the substrate surface to 50A. Sample No. 1 A ferromagnetic metal thin film was formed in the same manner as in 3. As a result, the coercive force was 1000 Oe and the residual magnetic flux density was 3800G.

[Example 2] A sample in which three ferromagnetic metal thin films were laminated was also prepared according to the sample preparation method shown in Table 1. The thickness of the ferromagnetic metal thin film of each sample is
The lower layer, middle layer, and upper layer were all 600A.

[0096] The same measurements as in Example 1 were carried out on these samples. The results are shown in Table 2 below.

[0097]

[Table 2]

From the results shown in Table 2, it can be seen that the present invention is highly effective also for magnetic recording media having a three-layered magnetic layer.

0099

Effects of the Invention The magnetic recording medium of the present invention can obtain a coercive force higher than the coercive force depending on the inclination of the columnar crystal grains with respect to the substrate. Moreover, on the contrary, it is possible to obtain a higher saturation magnetic flux density while maintaining a coercive force equivalent to that of the conventional method.

Claims (8)

[Claims] Claim 1: A magnetic layer having a magnetic layer on a substrate, the magnetic layer consisting of columnar crystal grains formed by an oblique evaporation method.
It has a structure in which ferromagnetic metal thin films of a number of layers or more and a non-magnetic thin film existing between adjacent ferromagnetic metal thin films are laminated, and the ferromagnetic metal thin films are arranged in a first group and a second group. , and the average growth direction of the columnar crystal grains of the ferromagnetic metal thin film belonging to the first group and the average growth direction of the columnar crystal grains of the ferromagnetic metal thin film belonging to the second group are based on the direction of the substrate. At least one side of the ferromagnetic metal thin film belonging to the first group and the ferromagnetic metal thin film belonging to the second group, which intersect with each other with the line in between, has a ferromagnetic metal thin film belonging to the second group, respectively. A metal thin film and a ferromagnetic metal thin film belonging to the first group are present, and for each ferromagnetic metal thin film, the angle between the average growth direction of columnar crystal grains and the main surface of the substrate is θ (however,
0<θ<90°), and the angle between the direction of the easy axis of magnetization after demagnetizing field correction and the main surface of the substrate is E (however, 0<E<90°).
A magnetic recording medium characterized in that θ>E, where θ>E. Claim 2: θ/E=1 for each ferromagnetic metal thin film
．． 2. The magnetic recording medium according to claim 1, wherein the following conditions apply. 3. The magnetic recording medium according to claim 1, wherein the nonmagnetic thin film contains as a main component an oxide of an element contained in the ferromagnetic metal thin film. 4. The magnetic recording medium according to claim 1, wherein the nonmagnetic thin film contains Co oxide as a main component. 5. The magnetic recording medium according to claim 1, wherein the thickness of the nonmagnetic thin film is 0.12 to 0.5 times the average thickness of the ferromagnetic metal thin film. 6. The magnetic recording medium according to claim 1, wherein the ferromagnetic metal thin film contains Co as a main component. 7. Fine particles are disposed on the surface of the substrate, and the center line average roughness R of the substrate after the fine particles are disposed.
7. The magnetic recording medium according to claim 1, wherein a is 40 A or less and a chain ratio of the fine particles is 70% or less. 8. The in-plane coercive force of the magnetic layer is 12
00 Oe or more, and the residual magnetic flux density is 4000
8. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is G or more.