JPS63281219A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To simultaneously realize high-density recording and improvement in S/N by forming a recording layer consisting of a thin ferromagnetic Co-Cr alloy film via an underlying layer consisting of a thin nonmagnetic Co-Cr-O alloy film on a substrate. CONSTITUTION:The thin nonmagnetic Co-Cr-O alloy film 12 is formed as the underlying layer between the substrate 11 and the recording layer in order to form the finer crystal grains of the thin ferromagnetic Co-Cr alloy film 13 constituting the recording layer. Namely, the finer crystal grains of the underlying layer are formed by intrusion of oxygen into the thin nonmagnetic Co-Cr alloy film 12 and the crystal grains of the thin ferromagnetic Co-Cr alloy film 13 formed thereon are also influenced by the underlying layer and are reduced in sizes. The thin ferromagnetic Co-Cr alloy film 13 of the recording layer is thereby provided with the fine crystal grains and large perpendicularly magnetic anisotropy in combination by which the high density recording and high S/N are simultaneously attained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention relates to perpendicular magnetic recording media, and in particular to ferromagnetic Co-
The present invention relates to a perpendicular magnetic recording medium having a recording layer made of a Cr-based alloy thin film.

(Prior Art) With the development of information processing technology, there is an increasing demand for larger capacities for magnetic recording media such as floppy disks. In response to this demand, active research and development is being carried out on perpendicular magnetic recording media, in other words perpendicular magnetic recording media, in which recording is performed using magnetization in a direction perpendicular to the film surface.

Perpendicular magnetic recording media are media with perpendicular magnetic anisotropy, and are made from Co-Cr alloys, etc., rather than coating-type media, which constitute most of the magnetic recording media for in-plane recording currently in use. A metal thin film type medium in which a recording layer is formed by forming a ferromagnetic metal thin film by vacuum evaporation or sputtering is expected to be a medium suitable for higher density recording.

By the way, in order to achieve high-density recording using the perpendicular magnetic recording method, a recording layer with large perpendicular magnetic anisotropy is required, and for this purpose, the crystal orientation of the ferromagnetic metal thin film must be improved. On the other hand, in order to obtain a large reproduction output and a good S/N ratio in a high-density region, it is necessary to make the unit magnetic particles constituting the recording layer as fine as possible. For example, in a ferromagnetic metal thin film such as a Co--Cr alloy formed by sputtering, each crystal grain corresponds to a unit magnetic particle, so the crystal grains must be made fine.

Although it is possible to make crystal grains finer by sputtering in an argon atmosphere into which an impurity gas such as oxygen is introduced, this method causes an extreme decrease in crystal orientation. This causes the perpendicular magnetic anisotropy to deteriorate.

In order to improve the crystal orientation of a ferromagnetic Co--Cr alloy thin film, a method of using an underlayer made of Ge or Ti is known (Japanese Patent Laid-Open No. 113122/1982). However, since these metal elements used in the underlayer easily combine with oxygen, there are problems in terms of uniformity and reproducibility.

Below the recording layer is a non-magnetic Co-Cr containing a higher Cr concentration than the ferromagnetic Co-Cr alloy thin film constituting the recording layer.
A method of improving vertical alignment by forming a thin film layer of a alloy has also been proposed (Japanese Unexamined Patent Publication No. 12232/1983). In this case, in order to improve the perpendicular alignment, it is necessary to increase the thickness of the non-magnetic Co-Cr alloy thin film layer, and therefore its internal stress becomes larger than that of the ferromagnetic Co-Cr alloy thin film of the recording layer. Therefore, large curls may occur in the medium. When curling occurs, the contact state of the magnetic head with the medium becomes unstable, and good recording and reproducing characteristics cannot be expected.

(Problems to be Solved by the Invention) As described above, in a perpendicular magnetic recording medium having a recording layer made of a conventional ferromagnetic Co-Cr alloy thin film,
It has been difficult to make crystal grains finer without impairing the crystal orientation of an o-Cr alloy thin film, and it has been difficult to achieve high-density recording and improvement in S/N at the same time.

Furthermore, when using an underlayer made of a thin Ge or Ti film to improve crystal orientation, there are problems in terms of uniformity and reproducibility. However, there was a problem in that it was difficult to improve the crystal orientation without causing curling.

Therefore, an object of the present invention is to provide a perpendicular magnetic recording medium in which the crystal grains of a ferromagnetic Co--Cr alloy thin film are made fine without impairing the crystal orientation, and high-density recording can be achieved without sacrificing S/N. With the goal.

In addition, the present invention has excellent uniformity and reproducibility, and can improve the crystal orientation of the ferromagnetic Co-Cr thin film without increasing the thickness of the underlayer to the extent that curling is likely to occur. The purpose is to provide a perpendicular magnetic recording medium that is possible.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for refining the crystal grains of a ferromagnetic Co-Cr alloy thin film constituting the recording layer. It is characterized by forming a nonmagnetic Co-Cr-0 alloy thin film as an underlayer.

Furthermore, in order to efficiently improve the crystal orientation of the ferromagnetic Co--Cr alloy thin film constituting the recording layer, the present invention also provides a base layer consisting of a Ge or Ti thin film between the substrate and the recording layer. The method is characterized in that a first underlayer and a second underlayer made of a nonmagnetic Co--Cr alloy thin film are sequentially formed.

(Function) When a base layer made of a non-magnetic Co-Cr-0 alloy thin film is formed, the crystal grains of the ferromagnetic Co-Cr alloy thin film that is the recording layer become fine, resulting in large reproduction even during high-density recording. Output and therefore high S/N can be obtained. That is, the incorporation of oxygen into the non-magnetic Co-Cr alloy thin film makes the crystal grains of the underlayer finer, and the crystal grains of the ferromagnetic Co-Cr alloy thin film formed thereon are also affected by the underlayer. It is then refined. In addition, non-magnetic Co-Cr as an underlayer
Although the crystal orientation of the -0 series alloy thin film decreases slightly due to the inclusion of oxygen, the ferromagnetic Co-Cr with a lower concentration of C
It shows good crystal orientation when compared to other alloy thin films. Therefore, due to the self-epitaxy effect, the ferromagnetic Co--Cr alloy thin film formed on the underlayer also exhibits relatively good crystal orientation.

By forming the non-magnetic Co-Cr-0 alloy thin film as the underlayer of the ferromagnetic Co-Cr alloy thin film in this way, the ferromagnetic Co-Cr alloy thin film of the recording layer can be formed perpendicular to fine crystal grains. It also has magnetic anisotropy, achieving high density recording and high S/N at the same time.

In addition, since the underlayer is non-magnetic, body magnetic charges are generated due to the difference in the amount of saturation magnetization at the interface with the recording layer, as in the case where a magnetic Co-Cr alloy thin film is used as the underlayer. It does not adversely affect the playback characteristics.

On the other hand, a first base layer made of a thin film of Ge or Ti;
When the second underlayer made of a nonmagnetic Co--Cr alloy thin film is laminated, the crystal orientation of the ferromagnetic Co--Cr alloy thin film serving as the recording layer is significantly increased, and a large perpendicular magnetic anisotropy is obtained. That is, the non-magnetic Co-C which is the second magnetic layer
Since the r-based alloy thin film exhibits better crystal orientation compared to a ferromagnetic Co-Cr-based alloy thin film with a lower Cr concentration, the ferromagnetic Co-Cr-based alloy thin film formed on the second underlayer Also shows relatively good crystal orientation due to self-epitaxy effect. If the second underlayer made of this non-magnetic Co-Cr alloy thin film is formed on the first underlayer made of a Ge or Ti thin film with better crystal orientation, the second underlayer is The orientation, and ultimately the crystal orientation of the recording layer, is improved to a level sufficient for practical use.

In addition, since the second underlayer in contact with the recording layer is nonmagnetic, the difference in saturation magnetization at the interface with the recording layer causes volume magnetization, as in the case where a magnetic Co-Cr alloy thin film is used as the underlayer. The generation of loads will not adversely affect the recording and reproducing characteristics.

(Example) First, an example according to the invention described in claim 1 will be described.

FIG. 1 is a sectional view schematically showing the structure of a perpendicular magnetic recording medium according to an embodiment of the present invention. In FIG. 1, the substrate 11 is a film-like substrate made of resin, and a carbon layer of non-magnetic Co-C is formed on both sides of the substrate 11 with a thickness of about 300 as an underlayer.
An r-0 alloy thin film 12 is formed on each film, and a ferromagnetic Go-Cr film with a thickness of about 0.3 μm is further formed thereon as a recording layer.
An alloy thin film 13 is formed respectively.

The nonmagnetic Co-Cr-0 alloy thin film 12 has a Cr concentration of 27w.
The value exceeds t%, for example about 30wt%, and Co-
RF in an oxygen-containing A atmosphere using a Cr target.
Formed by the magnetron spa power method. At this time, since a Co--Cr oxide thin film will be formed if the oxygen concentration is high, it is desirable to perform sputtering in an oxygen/Ar atmosphere with an oxygen concentration of 10% or less. A Co-Cr-0 alloy thin film with a Cr concentration exceeding 27 sit% has a saturation magnetization Ms
is smaller than that of the recording layer and can be considered non-magnetic.

The ferromagnetic Co-Cr alloy thin film 13 as a recording layer has a carbon concentration of 27 wt% or less, for example 20 wt%, and is formed by, for example, DC magnetron sputtering. It is oriented to have an axis of easy magnetization in the vertical direction, and has so-called perpendicular magnetic anisotropy.

In the perpendicular magnetic recording medium configured in this way, Co-C
The r-alloy thin film 13 has fine crystal grains and is made of Co-Cr.
The C-axis, which is the crystal axis of the substrate, is well oriented perpendicularly to the film surface (principal surface of the substrate 11), making it suitable for high-density recording, and at the same time provides large playback output and high S/N. It will be done.

Table 1 shows Co-C formed on base layers of various materials.
This figure shows the results of an experiment in which the crystal grain size, S/N, and recording density characteristics of an r-alloy thin film were investigated. The crystal grain size was measured by observing the surface of the ferromagnetic Co--Cr alloy thin film using a high-resolution scanning electron microscope.

The S/N and recording density characteristics were measured by contacting a ferrite ring head with a gap length of 0.3 μm while rotating a medium prepared in the shape of a 3.5-inch diameter floppy disk at 300 rotations per minute. All 1°S signals of NRZ I pattern are used for the recording signal, and the recording density is low (1kB).
The recording density characteristics were evaluated by measuring the recording density (D5o) that gives a reproduction output of 50% of the reproduction output in PI).

The larger the value of p5G, the higher the density of recording. Further, S/N is the ratio of reproduction output to noise at a recording density of 70 kBP+.

As is clear from Table 1, the concentration of C is 27.0w1%.
When a non-magnetic Co-Cr-0 alloy thin film exceeding Recording is possible.

FIG. 2 is a sectional view of a perpendicular magnetic recording medium according to another embodiment of the present invention, in which soft magnetic layers 22 with a thickness of, for example, 0.5 μm are formed on both sides of a heat-resistant film-like substrate 21, and For example, the thickness is 150 people and Cr9 degree is 28wt.
% non-magnetic Co--Cr--Mo-0 alloy thin films 23 are formed as underlayers, and ferromagnetic Co--Cr alloy thin films 24 are formed thereon as recording layers. As the soft magnetic layer 22, for example, a permalloy thin film is formed. In addition, the soft magnetic layer 22. Non-magnetic Co-Cr-M
o-0 alloy thin film 23 and ferromagnetic Co-Cr alloy thin film 2
4 is formed by a vacuum evaporation method.

In the perpendicular magnetic recording medium configured in this manner, good crystal orientation and high-density recording characteristics were obtained, similar to the perpendicular magnetic recording medium described in the previous example.

In the above two examples, a ferromagnetic Co-Cr alloy thin film was used as the recording layer, but for example, Co-Cr1.
: May contain a third element such as V, Rh, Ni, W, etc. In short, ferromagnetic Co-Cr whose main components are Co and Cr.
Any type alloy thin film may be used.

In addition, as an underlayer, a nonmagnetic (o-Cr-0 alloy thin film was used, but a layer with a third or fourth element added to Co, Cr, and O, such as Co-Cr-V-, 0, Co-
An alloy thin film such as Cr-Rh-0 or Co-Cr-N1-W-0 may be used, and in short, a non-magnetic Co-Cr-0 alloy thin film may be used. The material of the substrate can be selected from various materials such as AI, glass substrate, etc. Furthermore, the present invention can also be applied to a medium in which a recording layer is formed only on one side of the substrate.

Next, an embodiment according to the invention set forth in claim 5 will be described.

FIG. 3 is a cross-sectional view schematically showing the structure of a perpendicular magnetic recording medium according to an embodiment of the present invention. In FIG. 3, the base 3
Reference numeral 1 is a film-like substrate made of resin, and on both nine sides of this substrate 31, a first base layer with a thickness of about 300 mm is coated with a coal seam Ge thin film 32, and a second base layer is a coal seam layer with a thickness of about 300 mm. A non-magnetic Co-Cr-0 alloy thin film 33 of a magnetic Co-Cr alloy is formed, and a ferromagnetic Co-Cr alloy thin film 3 with a thickness of about 0.3 μm is further formed thereon as a recording layer.
4 are formed respectively. In the present invention, the non-magnetic Co--Cr alloy thin film may be a non-magnetic Co--Cr alloy thin film.

The nonmagnetic Co-Cr-0 alloy thin film 33 has a Cr concentration of 27w.
The value exceeds t%, for example about 30wt%, and Co-
RF using a Cr target in an Ar atmosphere containing oxygen
Formed by magnetomespapower method. At this time, if the oxygen concentration is high, a Co-Cr oxide thin film will be formed, so it is desirable to perform sputtering in an oxygen/A atmosphere with an oxygen concentration of 10% or less.
The Co-Cr-0 alloy thin film exceeding t% has a saturation magnetization Ms
is smaller than that of the recording layer and can be considered non-magnetic.

The ferromagnetic Co-Cr alloy thin film 34 as a recording layer has a carbon concentration of 27 wt% or less, for example 19 wt%, and is formed by, for example, DC magnetron sputtering. It is oriented to have an axis of easy magnetization in the vertical direction, and has so-called perpendicular magnetic anisotropy.

In the perpendicular magnetic recording medium configured in this way, the ferromagnetic C
The o-Cr alloy thin film 34 has C which is the crystal axis of Co-Cr.
The axes are extremely well oriented in the direction perpendicular to the film surface (main surface of the substrate 11) and have excellent recording density characteristics.

Table 2 shows the ferromagnetic C formed on the underlayer of various materials.
This figure shows the results of an experiment investigating the crystal orientation and recording density characteristics of an o-Cr alloy thin film.

Crystal orientation was evaluated by measuring the X-ray diffraction intensity (2) for the (002) plane of the ferromagnetic Co--Cr crystal.

(2) The larger the value, the better the crystal orientation. Note that ferromagnetic Co formed on a nonmagnetic Co-Cr thin film
The crystal orientation of the -Cr alloy thin film is evaluated by evaluating the difference between I of a non-magnetic Co-Cr alloy thin film and I when a ferromagnetic Co-Cr alloy thin film is formed thereon. Also,
The recording density characteristics are determined by rotating a floppy disk-shaped medium with a diameter of 3.5 inches at 300 revolutions per minute.
The measurement was carried out by contacting a ferrite ring head with a gap length of 0.3 μm. All 1°S signals of the NRZ I pattern are used for the recording signal, and the recording density (1kBPl) gives a reproduction output of 50% of the reproduction output at a low recording density (1kBPl).
D5o) was measured to evaluate recording density characteristics.

The larger D5o is, the higher the density recording is possible.

As is clear from Table 2, when a first underlayer made of a thin film of Ge or Ti and a second underlayer made of a nonmagnetic Co-Cr alloy thin film with a Cr concentration exceeding 27 wt% are formed, Since good crystal orientation is obtained and the value of D5o is large, good high-density recording is possible.

FIG. 4 is a cross-sectional view of a perpendicular magnetic recording medium according to another embodiment of the present invention, in which soft magnetic layers 42 having a thickness of, for example, 0.4 μm are formed on both sides of a heat-resistant film-like substrate 41.
On top of that, a Ti thin film 43 with a thickness of, for example, 200 mm as a first underlayer, and a Ti thin film 43 with a thickness of, for example, 200 mm as a second underlayer.
50 people received C "non-magnetic Co-Cr with a concentration of 27.5 wt%"
A -Nb alloy thin film 44 is formed, and a ferromagnetic Co--Cr alloy thin film 45 as a recording layer is further formed thereon. As the soft magnetic layer 42, for example, a permalloy thin film is formed. In addition, the soft magnetic layer 42°Ti thin film 43. The nonmagnetic Co-Cr-Nb alloy thin film 44 and the ferromagnetic Co-Cr alloy thin film 45 are formed by vacuum evaporation.

In the perpendicular magnetic recording medium configured in this manner, good crystal orientation and high-density recording characteristics were obtained, similar to the perpendicular magnetic recording medium described in the previous example.

In addition, in the above two examples, a ferromagnetic Co-Cr alloy thin film was used as the recording layer, but for example, V
, Rh, Ni, W, or other third elements. In short, any ferromagnetic Co--Cr alloy thin film containing Co and Cr as main components may be used.

In addition, although a nonmagnetic Co-Cr-0 alloy thin film was used as the underlayer, a layer obtained by adding a third element or a fourth element to Co or Cr, such as Co-Cr-V.

An alloy thin film such as Co-Cr-Rh or Co-Cr-Ni-W may be used, and in short, a non-magnetic Co-Cr-0 alloy thin film may be used. Various materials can also be selected for the base.

Furthermore, the present invention can also be applied to a medium in which a recording layer is formed only on one side of the substrate.

[Structure of the Invention] According to the present invention, a large perpendicular magnetic anisotropy can be achieved by forming a non-magnetic Co=Cr-○ alloy thin film as the underlayer of a recording layer made of a ferromagnetic Co-Cr alloy thin film. By making the crystal grains finer while maintaining the same, high S/N and high recording density characteristics can be obtained.

According to the present invention, a first layer made of a thin film of Ge or Ti is used as an underlayer of a recording layer made of a ferromagnetic Co-Cr alloy.
and a second layer consisting of a non-magnetic Co-Cr alloy thin film.
By forming the underlayer, crystal orientation is significantly better than when the underlayer is a single layer, and uniform and excellent high-density recording characteristics can be obtained.

Further, in the present invention, since the underlayer is non-magnetic, there is no possibility that volume magnetic charges are generated inside the recording layer, thereby impairing recording and reproducing characteristics.

Furthermore, according to the present invention, the same type as the recording layer, that is, Co--Cr
Because the recording layer and the underlayer have similar characteristics such as coefficient of thermal expansion due to the use of a base alloy based on the base layer, it is possible to use a film formation method in which the substrate is heated to a high temperature, such as sputtering or vacuum evaporation. Even in such cases, peeling between the recording layer and the underlayer is less likely to occur, and therefore durability can be improved.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are sectional views each schematically showing the structure of a perpendicular magnetic recording medium according to an embodiment of the present invention. 11,'21...Substrate, 12.23...Nonmagnetic Co
-C"-0 alloy thin film (base layer), 13.24... Ferromagnetic Co-Cr alloy thin film (recording layer), 22... soft magnetic layer, 31.41... base, 32... Ge thin film (first underlayer), 33.44...Nonmagnetic Co-Cr alloy thin film (second underlayer), 34.45...Ferromagnetic Co-Cr
Alloy thin film (recording layer), 42... Soft magnetic layer, 43...
Ti thin film (first underlayer). Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (8)

[Claims] (1) A perpendicular magnetic recording medium characterized in that a recording layer made of a ferromagnetic Co--Cr alloy thin film is formed on a substrate via an underlayer made of a non-magnetic Co--Cr-O alloy thin film. (2) The perpendicular magnetic recording medium according to claim 1, wherein the nonmagnetic Co-Cr-O alloy thin film constituting the underlayer contains more than 27 wt% of Cr. (3) The perpendicular magnetic recording medium according to claim 1, further comprising a soft magnetic layer between the substrate and the underlayer. (4) The perpendicular magnetic recording medium according to claim 1, wherein the underlayer and the recording layer are formed by a sputtering method or a vacuum evaporation method. (5) A recording layer made of a ferromagnetic Co-Cr alloy thin film is formed on the substrate via a first underlayer made of a Ge or Ti thin film and a second underlayer made of a non-magnetic Co-Cr alloy thin film. A perpendicular magnetic recording medium characterized in that it is formed by forming. (6) The perpendicular magnetic recording medium according to claim 5, wherein the nonmagnetic Co--Cr alloy thin film constituting the second underlayer contains more than 27 wt% of Cr. (7) The perpendicular magnetic recording medium according to claim 5, further comprising a soft magnetic layer between the substrate and the first underlayer. (8) The perpendicular magnetic recording medium according to claim 5, wherein the second underlayer and the recording layer are formed by a sputtering method or a vacuum evaporation method.