JPH04137217A - Magnetic disk having excellent magnetic characteristic and production thereof - Google Patents

Abstract

PURPOSE:To obtain the magnetic disk having excellent magnetic characteristics and recording and reproducing characteristics by forming a magnetic layer consisting of a thin metallic film of a polycrystalline body on a disk-shaped nonmagnetic substrate and respectively specifying the intra-surface magnetorestriction constant of the thin metallic film and the difference between the lattice direction in the radial direction and the lattice distortion in the circumferential direction thereof. CONSTITUTION:The thin metallic film of the polycrystalline body is formed on the disk-shaped nonmagnetic substrate having rigidity. This thin metallic film is so formed that the intra-surface magnetorestriction constant thereof is >=1.5X10<-5>, that the difference between the lattice distortion in the radial direction and the lattice distortion in the circumferential direction of the disk is negative and that the absolute value thereof is 0.1 to 0.7%. Namely, the anisotropy of the distortions generated in the magnetic film is utilized to enhance the magnetic anisotropy by a reverse magnetorestrictive effect. The magnetic disk which has the excellent magnetic characteristics and has the excellent reproduced output voltage value and SN among the recording and reproducing characteristics is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic disk with excellent magnetic properties and a method for manufacturing the same, and particularly relates to improving the recording and reproducing characteristics of a magnetic disk called a hard disk. .

(Prior Art) In recent years, magnetic disks, which are widely used as file memories in information processing systems, are required to have higher recording densities in order to increase their capacity. Therefore, in order to increase the recording density of magnetic disk media, it is necessary to reduce the distance between the magnetic disk and the magnetic head and to increase the recording and reproducing characteristics (SN ratio and output) of the magnetic disk. However, these two requirements are completely contradictory. However, in order to reduce the distance between the magnetic disk and the magnetic head, it is effective to reduce the surface roughness of the disk surface. This is because it is preferable to increase the surface roughness in order to increase the magnetic anisotropy.

By the way, in order to improve the recording and reproducing characteristics of a magnetic disk, it is necessary to increase the coercive force of the medium and to use a medium whose axis of easy magnetization is in the circumferential direction, that is, a medium having magnetic anisotropy. Therefore, conventionally, in order to increase the coercive force of the medium, it has been considered to control the components of the metal magnetic material and the film formation method. ,
15,000e or more is disclosed in IEICE Study Group Material 2 CPM 58-92 (1988) P, 23.

In addition, in order to impart magnetic anisotropy to the magnetic disk, Ap
It is effective to provide approximately concentric fine grooves on a non-magnetic substrate such as a plate, and such concentric fine grooves improve the SN ratio during recording and reproduction; ■It has been revealed that effects such as increased output during recording and playback can be achieved (US Patent No. 473).
5840 specification, Japanese Patent Application Laid-open No. 62-146434, etc.), and apart from such recording/reproducing characteristics, providing the above-mentioned fine grooves improves durability against friction with the magnetic head of the hard disk. It has been revealed that this method can improve the recording and reproducing characteristics (Japanese Patent Application Laid-Open No. 61202324), and is known as a means for improving recording and reproducing characteristics.

In particular, in the above US patent, in order to obtain magnetocrystalline anisotropy, the shadow effect of sputtered particles is induced by the unevenness of fine grooves, and the Cr intermediate layer formed thereon is (110
) plane is parallel to the disk surface, and furthermore, by causing the crystal orientation of the magnetic film formed on it,
It is said that the squareness ratio is improved, but in that case, the surface roughness needs to be 50 Å or more as measured by a roughness meter, and if it is less than that, the orientation of the C axis of the magnetic film is not constant, and the squareness ratio It has been shown that this decreases.

In addition, as an industrially usable device for forming fine grooves, as shown in the above-mentioned U.S. patent, an abrasive tape or free abrasive grains are pressed onto the surface of a substrate such as an AP board while rotating it. There is a device that can form fine grooves with good reproducibility, for example, at a depth of 1 to 0.2 am.
Fine grooves with a pitch of 00 lines/[[[[l are formed.

(Problem to be Solved by the Invention) However, when manufacturing the intended magnetic disk, simply providing fine concentric grooves on a substrate such as a /l plate as described above does not result in large magnetic anisotropy. is not obtained, and the magnitude of magnetic anisotropy is 1 to 3 × 10-”erg
/cc, and no significant improvement in the squareness ratio could be expected. Also, the shape (depth) of the groove.

width) and groove density (number of grooves per unit length in the radial direction)
The above-mentioned Japanese Patent Application Laid-Open No. 61-202324 discloses that the depth = 0,001
~0.2 μm, density = 400 to 1600 lines/hole, the recording and reproducing characteristics of the film-forming medium that provides the magnetic layer do not change much, therefore, simply providing concentric grooves does not. Although it is more effective in terms of recording and reproducing characteristics, the effect is limited. In particular, when the coercive force is large, specifically when the coercive force is 13,000e or more, simply providing a groove is insufficient because the squareness ratio is only 0.75 to 0.88, which is not so large. It is desired to improve the playback output.

In this way, conventionally proposed methods have attempted to improve the squareness ratio by using the magnetocrystalline anisotropy of the magnetic film, but have not been able to fully achieve this objective. .

In view of the above-mentioned circumstances, the present inventors conducted a detailed study on the mechanism of magnetic anisotropy that occurs when a magnetic film is formed on a substrate having concentric grooves. Magnetic anisotropy, which is centered on the axis of easy magnetization, can be enhanced by the inverse magnetostriction effect by utilizing the anisotropy of strain that occurs in the magnetic film. The present invention was completed by discovering the fact that it is possible to further improve the mold ratio and further improve the recording and reproducing characteristics.

Therefore, an object of the present invention is to provide a magnetic disk with excellent magnetic properties and a method for manufacturing the same, and also to provide a magnetic recording medium (magnetic The object of the present invention is to provide a high-coercivity covered disk for high-density recording.

(Means for Solving the Problem) In order to solve the problem, the present invention provides a magnetic disk in which a magnetic layer made of a polycrystalline metal thin film is formed on a rigid disk-shaped nonmagnetic substrate. , the in-plane magnetostriction constant of the metal thin film is 1.5X10-5 or more,
It is characterized in that the difference between the lattice strain in the radial direction and the lattice strain in the circumferential direction of the disk is negative, and its absolute value is 0.1 to 0.7%.

In addition, in order to manufacture such a magnetic disk, the present invention first forms an N1-P plating layer as an underlayer on a rigid disk-shaped nonmagnetic substrate, and then physically removes the surface of the N1-P plating layer. After polishing, the skin is removed with a pitch of about 500, and fine grooves with a depth of about 10 to 50 are created in the radial direction, and then on the N1-P plating layer or on the NiP plating layer. An intermediate layer containing Cr as a main component is placed on top of the layer.
After forming a film to a thickness of ~2,000 layers, a method is adopted in which a metal magnetic material having an in-plane magnetostriction constant of 1.5×10 −5 or more is formed on the intermediate layer.

(Function) In short, the present invention utilizes the anisotropy of strain generated in a magnetic film to increase the magnetic anisotropy by the inverse magnetostriction effect, and is based on the following idea.

That is, first, the magnitude (Ku) of in-plane magnetic anisotropy due to the inverse magnetostriction effect can be expressed by the following equation.

K u = 3/2λE (Eθ-cr) However, λ:
Magnetostriction constant E: Elastic modulus εθ: Circumferential crystal lattice strain Cr: Radial crystal lattice strain Therefore, in order to increase the magnetocrystalline anisotropy by the inverse magnetostriction effect, (a) λ〉0 and (εθ−εr)〉 0, that is, using a large magnetic film with a large λ and applying a large tensile strain in the circumferential direction, and (b) using a large magnetic film with λ<0 and (εθ−εr)<0, that is, 1λ1. Although a method of applying a large compressive strain in the circumferential direction may be considered, in the present invention, the above method (a) was used.

In order to realize the method (a), in the present invention, the in-plane magnetostriction constant of the polycrystalline metal thin film that provides the magnetic layer of the magnetic disk is 1.5XLO-5 or more. If the in-plane magnetostriction constant becomes smaller than this, the inverse magnetostriction effect becomes smaller and the object of the present invention cannot be fully achieved. Note that the in-plane magnetostriction constant of such a polycrystalline metal thin film is determined by the magnetic metal material.

In this way, in order to realize the method (a) above, in order to have a positive magnetostriction constant and increase its value, the magnetic material to be used is such that the magnetic layer is on an intermediate layer mainly composed of Cr. If formed, for example, Cot. If there is FezbTa4 (atomic ratio) and the intermediate layer is not formed, for example, C0yo~qoNi+o~30+ Co5s-ssN
i+o~3゜Cr5-+s+C0qa-qacr5
-zoTa+ -b + Co5o-qoPts-3S
There is Crs~15 (atomic ratio).

Further, in the present invention, the difference between the lattice strain (Cr) in the radial direction and the lattice strain (εθ) in the circumferential direction of the disk is negative, and the absolute value thereof is 0.1 to 0.7%. However, this makes (εr−εθ)<0 and gives a large compressive strain in the radial direction. Note that (εr−ε
When the absolute value of θ) becomes smaller than 0.1%, the inverse magnetostriction effect becomes low, and when the absolute value of (εr−εθ) exceeds 0.7%, problems such as deterioration of override characteristics occur. cause Also, (εr−εθ)<O,
In addition, as a measure to increase the absolute value, for example, N1
- Physically polish the underlying layer such as the P coating layer to form ultra-fine grooves in the radial direction. Note that the ultra-fine grooves mentioned here do not refer to grooves that can be measured with a surface roughness meter, as has been proposed in the past, but rather to surface irregularities that can be measured using a scanning tunneling microscope. . In short, grooves made up of irregularities that are much smaller than conventional irregularities are provided in the radial direction to induce compressive strain in the magnetic film in the radial direction. Then, on the substrate with such ultra-fine grooves,
Alternatively, by forming an intermediate metal layer such as a Cr film on the substrate and then forming a magnetic film such as a Co alloy type film on top of the intermediate metal layer such as a Cr film,
By making the absolute value of εr−εθ) sufficiently large, the inverse magnetostrictive effect can be effectively expressed.

By the way, the magnetic disk according to the present invention, particularly the hard disk, generally has a base layer such as an N1-P plating layer on a rigid disc-shaped non-magnetic substrate, and on this base layer or on the base layer. On top of this, there is a non-magnetic metal intermediate layer made of an alloy containing Cr as a main component, on top of which a metal thin film magnetic layer is provided, and furthermore, a protective film and a lubricating film are provided on top of this. As a non-magnetic substrate used in manufacturing magnetic disks, A! or their alloys, glass, ceramic fuchs, engineering plastics, and other known materials.

Further, the thickness of such a substrate is generally 0.5 mm to 1.9 mm.
It is about the size of a picture and is used in a donut-shaped disc shape. Among these, the substrate material is generally AA gold alloy among the above-mentioned materials, and a predetermined underlayer, for example, an N1-P coating layer, is formed on such a substrate by electroless plating.

Then, the substrate provided with such an underlayer is subjected to an appropriate polishing operation as in the conventional case, and the surface roughness of the magnetic disk is determined from the flying height of the magnetic head. In general, it is effective to reduce surface roughness to prevent the head from colliding with protrusions on the substrate when it is flying; Therefore, the surface roughness (Ra value) is selected to be appropriate based on the magnitude of the motor starting torque value of the disk drive and the flying height of the head.

Next, on the base layer of the substrate that has been subjected to this normal polishing operation, physical polishing is performed to make (εr−εθ)<0 and increase the absolute value on the unevenness. Ultrafine grooves are formed in the radial direction. As mentioned above, these ultra-fine grooves are not grooves (irregularities) that can be measured with a conventional surface roughness meter, but are much smaller.

It is measured using a scanning tunneling microscope (for example, using a nanoscope, horizontal 1.5 x 105 x / 11
106 times), it has a pinch of about 500 or less, which is narrower than the conventional groove pinch of 20.2 μm, and even if the depth (height) is 10 to 50 It has a diagonal plate the size of a human, and the presence of such ultra-fine grooves in the radial direction has the effect of inducing compressive strain on the surface of the magnetic layer.

In addition, since ultra-fine grooves can be distinguished from conventional grooves, even if conventional grooves measured using a surface roughness meter are provided in the circumferential direction, they are also circular. Even if it is provided along the radial direction instead of the circumferential direction, or even if it is provided isotropically, if the above-mentioned fine grooves are provided in the radial direction, compressive strain will not occur in the magnetic film. It is possible to fully exhibit the effect of inducing .

In addition, on a substrate provided with such ultra-fine grooves, or on top of which a Cr-based film containing Cr as a main component is formed as an intermediate layer, a magnetic film such as a Co alloy-based film may be used. (magnetic layer) is formed. Note that the crystal orientation of the Cr-based film as the intermediate metal layer is that in the conventional example, the (110) plane is parallel to the disk surface, but in the present invention, the (110) plane is parallel to the disk surface.
0) The surface is parallel to the disk surface. To this end, while conventionally the heating temperature during sputter deposition of Cr-based films and magnetic films is 150 to 250'C,
The temperature is increased to 250-300"C, and the ultimate vacuum degree of the sputtering chamber is 5 X 10-6 Torr, whereas in the present invention, the vacuum level is less than I X 10-" Torr, preferably 2 X 10-' Torr or less.

Further, the Ar gas pressure during sputtering is preferably 2 to 10 mmTorr when forming either the Cr-based film or the magnetic film. Note that when the Ar gas pressure (sputtering atmosphere pressure) during sputtering is 20 to 40+nm Torr, the C axis of the cobalt alloy-based magnetic film or the like is within the disk plane, but its direction is random.

In addition, in the present invention, the thinner the intermediate metal layer such as a Cr-based film formed by such a sputtering method is (εr
Although it has been recognized that the absolute value of -εθ) increases and the squareness ratio improves, if the film thickness becomes too thin, the coercive force decreases, which is not preferable. In the present invention, in order to have a sufficiently large absolute value of (εr- and θ) and to advantageously exhibit the inverse magnetostriction effect, the thickness of the Cr-based film, etc. is 15
It is said to be between 0 and 2000 people.

Thereafter, after such a magnetic film (magnetic layer) is formed by sputtering, a carbon protective film and a lubricating film are sequentially formed on top of it in the same manner as in the past, thereby forming the intended magnetic disk. It is said that

The magnetic disk of the present invention has a large in-plane magnetic anisotropy, and therefore improves the recording and reproducing characteristics of the magnetic disk. This is also due to an increase in coercive force, which prevents domain wall movement. That is, this coercive force has a value of 0.85 to 1.0 times the coercive force in the circumferential direction, which was conventionally considered to have a correlation with the SN ratio, and has a correlation with the SN ratio. It is presumed that the formation of the ultra-fine grooves mentioned above also contributes to an improvement in the coercive force that prevents domain wall movement in the circumferential direction.

(Examples) Below, some examples of the present invention will be shown to clarify the present invention more specifically.

First, Ar-Mg with a diameter of 130 mm and a thickness of 1.92 mm.
An alloy (JIS-A5024 alloy) substrate was used, and an N1-P underlayer having a thickness of 18 μm was formed on this substrate by a known electroless plating method. After that, alumina free abrasive grains were used as an abrasive, and a texture device (USA: 5 trassb) was used.
(manufactured by au) to perform texture polishing, and
Irregularities were added to the surface of the base layer. The surface of this texture-polished base layer has a radial surface roughness (Ra) of 40 as measured by a surface roughness meter using a 2.5 μm square stylus, and a circumferential surface roughness of 40. In Ra, there were 40 people.

Next, ultrafine irregularities were further formed in the radial direction on the texture-polished disk substrate in the following manner. That is, a commercially available final tape polish machine (USA: ExclusiveDesign C
While rotating the substrate, a polishing tape was pressed against the substrate while vibrating in the radial direction, thereby forming ultrafine radial irregularities on the surface of the substrate. Note that polyester resin tape was used as the polishing tape, and the polishing was repeated 5 times/5 times.
Min rotation speed, vibration frequency: 100 times/min, contact pressure =
It was processed for 5 minutes at 2 kg/cTIT. Additionally, cooling lubricant was applied to prevent seizure during machining.

In the thus obtained disk substrate, the surface roughness was unchanged from before the processing process despite the ultrafine unevenness processing described above, and the Ra was 40 in both the radial and circumferential directions. Ta. However, in the case where this ultra-fine unevenness processing step was implemented (Invention Example 1) and the case where such a step was omitted (Comparative Example 1), the substrate after sputtering film formation was examined using a scanning tunneling microscope. As a result of observation using
It was observed that unevenness with a height of about 30A was created in the radial direction.

Then, a metal intermediate layer, a magnetic layer, and a carbon protective layer were sequentially formed by sputtering on the thus obtained disk substrate having ultrafine irregularities.

That is, the metal intermediate layer, the magnetic layer, and the carbon protective film are formed so that when the disk substrate is placed in a vacuum chamber and the circular target and the substrate are coaxially stationary and facing each other, the ultimate vacuum level is I x 10-' Torr. After increasing the degree of vacuum until
It was formed by continuous sputtering film formation. Note that the metal intermediate layer was a Cr film, and its thickness was 300. Further, the magnetic layer contains co=70 at%, Fe: 26 at%, Ta:
An OCO alloy having a composition of 4 atomic % was used, and the film thickness was 500 mm. At this time, the substrate bias is -300
■ was applied. Furthermore, the thickness of the carbon protective film was 400. In addition, the Ar gas pressure during film formation was 5 m
The mTorr and DC power were both 3kW.

While the thus obtained magnetic disk is referred to as Invention Example 1,
A magnetic disk obtained in the same manner except that the ultrafine unevenness processing was not performed was used as Comparative Example 1 for later performance comparison.

Furthermore, the thickness of the Cr film as the metal intermediate layer was set to 800 layers as Invention Example 2, and the heating temperature at the time of melting and heating was set to 295°C, and the thickness of the Cr film was set to 200 layers. The magnetic disk was designated as Invention Example 3.

Furthermore, CO:88 was used as the magnetic layer without forming a metal intermediate layer.
C with a composition of atomic %, Cr: 9 atomic %, Ta: 3 atomic %
Invention Example 4 was a magnetic disk that was the same as Invention Example 1 except that an o-based alloy was used.

On the other hand, in the same process as above, the thickness of the Cr film was 300 mm.
Comparative Example 2 was a magnetic disk in which no person was detected. Also Co
Comparative Example 3: A magnetic disk having a magnetic layer with a small absolute value of magnetostriction constant obtained by sputtering film formation using a Co-based alloy having a composition of 7 at% Ni, 20 at% Cr, and 3 at% Ta. And so.

Further, the disk substrate on which the N1-P plating underlayer is formed, without using the above-mentioned texturing device,
Tape polishing equipment (USA: ExclusiveDesi
gn Company), polishing tape number #4000, contact pressure crab 0.8 kg/c.
f, without radial vibration, tape polishing was performed at a work rotation speed of 140 times/min, and after forming circumferential grooves on the disk substrate, ultimate vacuum: 1 x 10-5T
orr, heating temperature: 200'C, Cr film (metallic intermediate layer), Conia 0 atomic%, Fe: 15 atomic%
, Cr: 11 at%, Ta: 4 at%.
Comparative Example 4 was obtained by depositing a magnetic layer made of an O-based alloy and the thickness of the Cr film was prepared by 1500 persons, and Comparative Example 5 was obtained by forming a magnetic layer made by 500 persons.

For the thus obtained magnetic disks of Invention Examples 1 to 4 and Comparative Examples 1 to 5, the difference in lattice strain (εr−εθ) between the radial direction and the circumferential direction was measured, and the results were as follows. The recording and reproducing characteristics and magnetic properties (magnetostriction constant of the magnetic film, coercive force in the circumferential direction, coercive force that prevents domain wall movement in the circumferential direction) of each magnetic disk are shown in Table 1 below.

The lattice strain of the magnetic film (layer) of the magnetic disk was determined by measuring the lattice spacing of Co (1011) in two directions (α'-40°,
β-0°, 90°), and according to the following relational expression (
The value of εr−εθ) was determined.

However, dr: radial direction, lattice spacing measured at α'-40° dθ - circumferential direction, lattice spacing measured at α'=40° As is clear from Table 1 below, invention examples 1 to 4 Magnetic disks have different recording and reproducing characteristics (output, resolution, SN ratio,
It is recognized that the magnetic disks are superior to the magnetic disks of Comparative Examples 1 to 5 both in terms of override) and magnetic properties (squareness ratio).

(Effects of the Invention) As is clear from the above description, according to the present invention, a magnetic disk can be provided which has excellent magnetic properties, and further has excellent recording and reproducing properties, particularly in the reproduction output voltage value and the S/N ratio. This can greatly contribute to the realization of high-density recording on magnetic disks.

Applicant: Sumitomo Metal Mining Co., Ltd. Sumitomo Light Metal Industries, Ltd. Sumitomo Metal Industries, Ltd.

Claims (4)

[Claims] (1) A magnetic disk in which a magnetic layer made of a polycrystalline metal thin film is formed on a rigid disk-shaped nonmagnetic substrate, and the in-plane magnetostriction constant of the metal thin film is 1.5 × 10.
^-^5 or more, the difference between the lattice strain in the radial direction and the lattice strain in the circumferential direction of the disk is negative, and its absolute value is 0.1
~0.7%. A magnetic disk with excellent magnetic properties. (2) The magnetic disk according to claim 1, wherein the magnetic layer is formed on an intermediate layer mainly composed of Cr and having a thickness of 150 to 2000 Å. (3) After forming a Ni-P plating layer as a base layer on a rigid disk-shaped nonmagnetic substrate, the surface of the Ni-P plating layer is physically polished to a pitch of about 500 Å or less and a depth of about 500 Å or less. Ultra-fine grooves with a diameter of approximately 10 to 50 Å are provided in the radial direction, and then a metal magnetic material having an in-plane magnetostriction constant of 1.5 x 10^-^5 or more is formed on the Ni-P plating layer. A method for manufacturing a magnetic disk with excellent magnetic properties. (4) After forming a Ni-P plating layer as an underlayer on a rigid disk-shaped nonmagnetic substrate, the surface of the Ni-P plating layer is physically polished to a pitch of about 500 Å or less and a depth of about 500 Å or less. ultrafine grooves with a diameter of about 10 to 50 Å are formed in the radial direction, and then an intermediate layer containing Cr as a main component is formed to a thickness of 150 to 2000 Å on the Ni-P plating layer, and then On the layer, the in-plane magnetostriction constant is 1.5×10
^-^ A method for manufacturing a magnetic disk with excellent magnetic properties, characterized by forming a film of a metal magnetic material of 5 or more.