JPS6356812A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease noise and to improve S/N by forming an intra-surface magnetized layer which is a lower layer of a perpendicular magnetic recording medium having two-layred structure to the coercive force larger than heretofore. CONSTITUTION:The intro-surface magnetized layer 2 is provided to the lower layer of the perpendicular magnetic recording medium having the two-layered structure. The coercive force of the layer 2, which is heretofore <=5 (Oe), is specified to the consideably increased range; i.e., 50-300 (Oe) and the coercive force of the perpendicularly magnetized layer 3 is set within the prescribed range corresponding thereto, by which the fluctuation in the magnetic moment is decreased and the generation of magnetic walls is eventually suppressed. The S/N at the time of reproduction is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a two-layer perpendicular magnetic recording medium having an in-plane magnetization layer as a lower layer, and particularly to a perpendicular magnetic recording medium having an S/N ratio superior to that of conventional ones, that is, a sufficiently high S/N ratio. The present invention relates to a two-layer perpendicular magnetic recording medium having excellent recording sensitivity and reproduction output.

BACKGROUND ART Magnetic recording involves converting an electrical signal into a magnetic signal via a magnetic head, and leaving the signal in the form of a minute permanent magnet in the magnetic layer of a thin film tape or disk.

Traditionally, such magnetic recording methods have been based on a method called horizontal recording, in which the magnetic layer of a tape, which is a magnetic recording medium, is magnetized in the longitudinal direction of the tape surface, and most current magnetic recording also uses this method. It is.

However, this method has a fundamental problem in the magnetic layer of the tape: the N and N or S and S magnetic poles of the magnets face each other and repel each other, creating a demagnetizing field and reducing the signal voltage. was.

In particular, the above problem becomes more pronounced as the wavelength of the signal becomes shorter.

In recent years, in response to increased recording density and shorter signal wavelengths, Co
A perpendicular magnetic recording system comprising a -Cr film was proposed by Iwasaki et al. and is attracting attention. In such a perpendicular magnetic recording system, the magnetic layer is magnetized perpendicularly to the surface, leaving magnets that are antiparallel to each other for every half wavelength of the signal.Therefore, on both sides of each magnet (i.e. recording bit) Since the magnets are always oriented in opposite directions, an attractive force acts on all the magnets, and in principle there is no demagnetizing field that would cause problems in the horizontal direction.Therefore, the recording and reproduction sensitivity for low wavelength signals is greatly improved. Moreover, the recording density is several times higher than that of horizontal recording, and it is said that this method will lead to future applications in computer memory.

Now, regarding such perpendicular magnetic recording media, instead of using a single layer of perpendicular magnetic recording layer on the substrate, a high magnetic permeability, low coercivity material such as Fe-Ni or Fe is used between the substrate and the perpendicular magnetic recording layer. By using it as a perpendicular magnetic recording medium with a two-layer structure (hereinafter referred to as a two-layer medium) in which an in-plane magnetization layer with high magnetic force and high saturation magnetization is formed, the recording sensitivity and reproduction sensitivity are one order of magnitude higher than those of the single-layer type mentioned above. It has been discovered that this technology improves performance, and is currently in the development and research stage with the aim of practical application both inside and outside of I.

Problems to be Solved by the Invention The two-layer medium has a 7-Fe2O3 film having the same magnetization mode as in-plane magnetic recording in the lower layer, and a Co-Cr film or the like in the upper second layer. A perpendicular magnetic recording medium made of a Co alloy film is formed. Because the magnetic moments generated in the perpendicular direction in the second layer are arranged antiparallel to each magnetic domain, the in-plane magnetic moments in the first layer are such that magnetic moments of the same polarity face each other in adjacent magnetic domains. forming a state. The in-plane magnetization layer in conventional two-layer media has a relatively low coercive force of less than 5 oersteds (Oe), and because the saturation magnetization is large, the repulsion between magnetic moments of the same polarity causes the magnetization transition region to expand. . Therefore, the fluctuation of the magnetic moment in this magnetization transition region becomes extremely large, and the bit state cannot be stably maintained. The instability of this bit becomes more pronounced as the demagnetizing field becomes larger as the recording density becomes higher. Ohmukai et al. experimentally verified this phenomenon using a Lorentz electron microscope (National Conference on Semiconductor Materials, Institute of Electronics and Communication Engineers) In addition, in films with high permeability and low coercive force, a domain wall is introduced between the perpendicularly magnetized layer, which is the upper layer, to reduce the demagnetizing field within the film. Therefore, irregular magnetic flux unrelated to the recording signal leaks to the top of the medium from the region where the magnetic moment fluctuates and from the domain wall part, and this causes noise during playback. Furthermore, since the saturation magnetization of the second layer is relatively large, the leaking magnetic flux cannot be ignored, and reducing this noise is a major challenge for dual-layer media.

Therefore, an object of the present invention is to provide a two-layer perpendicular magnetic recording medium with an excellent S/N ratio and capable of high-density recording.

Means for Solving the Problems In order to solve the problems of the conventional two-layer perpendicular magnetic recording medium as described above, the inventors of the present invention have conducted intensive studies and research, and found that the in-plane magnetization layer, which is the lower layer, It has been found that by increasing the coercive force compared to the conventional one, it is possible to reduce the noise generated by the fluctuation of the magnetic moment and improve the S/N ratio as a result.

That is, the present invention provides a substrate, an in-plane magnetization layer provided on the substrate with an in-plane coercive force of 50 to 300 (Oe), and a perpendicular coercive force provided on the in-plane magnetization layer. 5
The present invention provides a two-layer perpendicular magnetic recording medium having a perpendicular magnetization layer of 00 to 1500 (Oe).

First, in the two-layer medium of the present invention, the in-plane magnetization layer, which is the first layer on the substrate, has a coercive force of 50 to 300 in order to achieve the objective of the present invention, which is to improve the S/N ratio. (
must be within the range of Oe).

If the coercive force is not within this range, no improvement in the S/N ratio will be observed, which is not preferable.

The material for such an in-plane magnetization layer may be one that is normally used as an in-plane magnetization layer in a two-layer medium, such as 7
-Fe2O3, NiCoP, Co-Pt and the like. When forming an in-plane magnetization layer with these materials,
The coercive force can be appropriately adjusted within the above range by adjusting the sputtering conditions and the amount of added elements during thin film formation. In the case of Co-Pt, the coercive force can be adjusted by adjusting the Pta degree, and by changing the pt1 degree in Co-Pt in the range of 1 to 10%, the coercive force can be adjusted from 20 to 10%.
It is known that the value changes monotonically at 600 (De). The thickness of such an in-plane magnetization layer is not particularly limited, and may be the thickness of an in-plane magnetization layer in a normal two-layer medium.
Generally, about 1.5 μm is sufficient.

Next, in the two-layer medium of the present invention, Co-Cr, which is usually attracting attention in perpendicular recording systems, is suitable for the second layer of perpendicular magnetic recording medium formed on the first layer.
In addition, for example, MnB15TbFeSCdC.

Examples include amorphous thin films of rare earth element-transition element alloys (RE-TM), Ba ferrite films, etc. The coercive force of this perpendicular magnetic recording medium is desirably 500 to 1500 (Oe) by adjusting the composition of Co and Cr. If the coercive force is not within this range, the S/N ratio will decrease due to the balance with the underlying in-plane magnetization layer, which is not preferable. The thickness of this second layer is not particularly limited, and may be the thickness of the perpendicular magnetic layer in a normal two-layer medium, usually 1.5
A thickness of approximately μm is sufficient.

Next, as the substrate in the two-layer medium of the present invention, for example, a nonmagnetic substrate such as AI, glass, or Si is suitable.

The two-layer medium of the present invention has the above-mentioned structure, but as a method for manufacturing such a two-layer medium, first, the above-mentioned in-plane magnetization layer is deposited on the above-mentioned substrate by a sputtering method. form. This can be carried out, for example, by a high frequency sputtering method. In order to form a Co-pt in-plane magnetization layer on a substrate by this method, a composite target in which a PT receipt is arranged on Co is used as the sputtering condition. It is preferable to control the composition of Co--Pt by the number of sheets, and to use an inert gas such as Ar at about 2 XIO' Torr for the atmosphere.

Next, the perpendicular magnetization layer as the second layer is formed on the second layer thus formed on the substrate by a spacking method or the like. For example, when forming a Co-Cr film, using RF sputtering, a Co-Cr alloy is used as the target, the atmosphere is argon gas at about 2X 1O-2 Torr, and the substrate temperature is 1.00°C. The front and back are preferred.

The bilayer medium of the present invention can be obtained by the above-mentioned method.

A perpendicular magnetic recording medium with a working two-layer structure has an in-plane magnetization layer as the lower layer, so that during recording, the magnetic flux that is the recording signal is transmitted from the auxiliary magnetic pole that makes up the recording head to the white magnetization layer on the substrate. pass horizontally to the center and gather at the center,
This has the advantage of strongly magnetizing the perpendicularly magnetized layer directly above it.

- In addition, in the state of residual magnetization, the antiparallel magnetic moments in the perpendicular magnetization layer form a horseshoe-shaped magnet through the magnetic moment near the surface of the in-plane magnetization layer, which causes the magnets to strengthen each other. I keep it.

Based on these facts, it is said that the recording/reproducing sensitivity of a dual-layer medium is about 10 times higher than that of a single-layer perpendicular recording medium, and that the storage life is sufficiently long.

However, in the in-plane magnetization layer of conventional two-layer media, the magnetic moments forming the above-mentioned horseshoe-shaped magnet exist with the same poles facing each other, and in particular, this in-plane magnetization layer Due to the low coercive force and large saturation magnetization, the influence of the demagnetizing field between the magnetic moments of the same polarity was noticeable. That is, the magnetic moments repel each other, the magnetization transition region expands, and the fluctuations of the magnetic moments around the region become significantly large, making it impossible to maintain the bit state stably. In addition, a domain wall is formed near the surface of the lower in-plane magnetization layer, which is the back surface of the upper perpendicular magnetization layer, and its removal becomes difficult. Due to the generation of domain walls and the above-mentioned fluctuation of the magnetic moment, irregular magnetic flux other than signals leaks to the top of the medium during reproduction of the recording medium, causing an increase in noise.

The present inventors noticed the relationship between the fluctuation of the magnetic moment of the in-plane magnetized layer and the generation of domain walls and the IH5,>2 force of the in-plane magnetized layer, and the coercive force, which was conventionally less than 5 (Oe), was Significantly increased range, i.e. 50-300 (
It has been found that the fluctuation of the magnetic moment can be reduced by adjusting the coercive force of the perpendicular magnetization layer to a predetermined range, and thereby the generation of domain walls can be suppressed. Therefore, a two-layer medium consisting of a combination of an in-plane magnetization layer and a perpendicular magnetization layer having a coercive force within the above range can significantly improve the S/N ratio during reproduction.

EXAMPLES Hereinafter, the present invention will be specifically explained using examples and production examples, but the present invention is not limited by these in any way.

Example 1 FIG. 1 shows a schematic diagram of a two-layer medium of the present invention. A non-magnetic substrate 1 has an in-plane magnetization layer 2 formed thereon, and a perpendicular magnetization layer 3 formed thereon.

Hereinafter, the method for producing the two-layer medium of the present invention and the effects produced by the medium will be explained using production examples.

Fabrication Example 1 In this example, a two-layer medium is formed, with a Co-Pt in-plane magnetization layer as the first layer and a co-Cr perpendicular magnetization layer as the second layer on a 5-inch Sl wafer disk substrate. A device having the configuration shown in FIG. 1 was manufactured. First, a layer of 0.15 μm of membrane rhinoceros was deposited on the substrate using the high-frequency spackle method.
A Co--Pt in-plane magnetization layer of m was formed. As for sppacking conditions, a composite target consisting of PT sheets arranged on Co was used as a target, and depending on the number of sheets, Co
The composition of -Pt was prepared, argon gas was used as the sputtering atmosphere, and the internal pressure of the container was adjusted to 2 Xl0-3 Torr. FIG. 2 is a graph plotting the relationship between Co--Pt in-plane magnetization layers having various pt1 degrees obtained by the composite target as described above and their coercive force. From this, C.

-The coercive force increases monotonically as the pt concentration in Pt increases, and the coercive force increases from 20 to 6 in the range of 1 to 10 at% Pta.
00 (Oe).

Next, in order to form a perpendicular magnetization layer on the Co Pt in-plane magnetization layer formed on the substrate with various Pt concentrations as described above, a Co
-A Cr film was formed. As spuck conditions, a Co-Cr alloy with a Cr concentration of 21 at% was used as the target, argon gas was used as the sputtering atmosphere, the pressure inside the container was adjusted to 2 X IQ-2 Torr, the sputtering power was 500 W, and the substrate temperature was was maintained at 100°C. In this way, the two-layer media of the present invention for the various degrees of PtJ described above were obtained.

Performance Measurement In order to measure the coercive force and saturation magnetization of the above perpendicular magnetic layer, a perpendicular magnetic layer made of Co-Cr was formed on the substrate using the same method and conditions as above, and the coercive force and saturation magnetization were measured. When measured, the coercive force was 1000 (Oe) and the saturation magnetization was 4000 G.

Next, in order to find the relationship between the coercive force of the in-plane magnetization layer and the S/N ratio, for the various two-layer media with Pj' of 3 degrees obtained in Production Example 1, the gap length was 0.15 μm, the core width was 20 μm,
Using a thin film head with a coil turn number of 18 μm, the peripheral speed is 1.
Recording was performed under the conditions of 0 m/s and a flying height of 0.1 μm, and the S/N ratio was measured by reproduction. FIG. 3 plots the relationship between the coercive force of the in-plane magnetization layer and the S/N ratio. From this figure, the limited range of the coercive force of the in-plane magnetization layer of the present invention is 50 to 300.
(Oe), the S/N ratio is 30 dB or more,
A maximum S/N ratio of 35 dB can be obtained. On the other hand, as shown in FIG. 3, the coercive force of the in-plane magnetization layer corresponding to the conventional two-layer medium is as low as 5 (Oe) or less, and if it is not within the scope of the present invention, the S/N ratio is also about 28 dB. low. In addition, typical two-layer media used in the past (in-plane magnetization layer is F
e N+ (81 atomic% N+), and its coercive force 1
(Oe), saturation magnetization 10000G) S/N ratio is 28
dB, the S/N of the dual-layer medium of the present invention is
It can be seen that the ratio is particularly excellent with a maximum of 35 dB.

Fabrication Example 2 In this example, a T-Fe203 in-plane magnetization layer was provided as the first layer on a 5-inch Sl wafer disk substrate, and a perpendicular magnetization layer of Co-Cr was provided on the second layer. 1
A two-layer medium with the configuration shown in the figure was formed.

First, a 7-Fe 20° in-plane magnetization layer having a thickness of 0.15 μm was formed on the substrate using magnetron sputtering as follows. To obtain γ-Fe2O3, 98 atomic percent (at%) of Fe and the balance of C were added to the target.
Using an alloy consisting of u, 50 [1
Using a 101% 0□-5Omo1%Ar mixed gas, adjusting the container internal pressure to 3 X 1O-3Torr and setting the spack power to 0.3KW, we first deposited α-
Fe20* was obtained.

This a-Fe203 film was heated at 320°C in an H2 atmosphere for 3
By heating and reducing for a period of time, a thin film containing Fe3O4 as the main component was obtained.
Furthermore, thermal oxidation was performed at 315°C for 4 hours in the air.
A film containing γ-Fe2O3 as a main component was obtained. When the magnetic properties of the 7-Fe2O film thus obtained were measured, the coercive force was 200 (Oe) and the saturation magnetism was 3200 G.
1 residual magnetization was found to be 2700 G. It has been confirmed that the coercive force of this γ-Fe2O3 film can be varied from 100 to 600 (Oe) by adjusting the additives and the spack gas pressure.

Co-Cr is used as a perpendicular magnetization layer on this r-Fe203 film.
A film was deposited in the same manner as in Preparation Example 1.

When the recording and reproducing characteristics of the dual-layer medium thus obtained were measured in the same manner as the performance measurement described above, an S/N ratio of 35 dB was obtained at recording densities DS[+=4000 bpm and 2000 bpm. The S/N ratio is improved by 7 dB compared to the conventional S/N ratio, and it can be seen that the dual-layer medium of the present invention is superior.

Effects of the Invention As explained above, the two-layer medium of the present invention is capable of reducing noise caused by fluctuations in the magnetic moment in the in-plane magnetization layer and noise from domain walls, and is sufficiently superior to conventional two-layer media. Since a high S/N ratio can be obtained, this method is extremely useful in the practical application of perpendicular magnetic recording media.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the dual layer media of the present invention. FIG. 2 is a graph showing the relationship between the Pta degree and the coercive force in the in-plane direction in a Co--Pt in-plane magnetization layer. FIG. 3 is a graph plotting the coercive force of the Co--Pt in-plane magnetization layer and the S/N ratio of the two-layer medium.

Claims (1)

[Claims] The holding force in the in-plane direction of the substrate provided on it is 50 to 3
1. A two-layer perpendicular magnetic recording medium having an in-plane magnetization layer with a magnetic field strength of 0.00 Oe and a perpendicular magnetization layer with a coercivity in the perpendicular direction of 500 to 1500 Oe provided on the in-plane magnetization layer.