JP3102638B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording technique, and more particularly to a recording / reproducing apparatus using a perpendicular magnetic recording medium suitable for high-density recording.

[0002]

2. Description of the Related Art In-plane magnetic recording systems are used in magnetic disk drives that are currently in practical use. The recording method uses a magnetic film that is easily magnetized in a direction parallel to the disk surface, and forms a magnetic domain in an in-plane direction for recording. The recording density of magnetic disk devices is increasing year by year,
Along with this, the thickness of the magnetic film has been reduced. The reason for thinning the magnetic film is that in the case of longitudinal magnetic recording, the magnetic field generated from the magnetic domain boundaries hinders the formation of minute magnetic domains. It is reduced. However, as the magnetic film becomes extremely thin,
This time, even at room temperature, the fluctuation of the magnetization due to heat occurs, which causes a problem that the recording magnetization decreases.

As a technique for overcoming such a problem of the in-plane magnetic recording system, a perpendicular magnetic recording system using a magnetic film which is easily magnetized in a direction perpendicular to the disk surface has been proposed. In perpendicular magnetic recording, since there is no problem in in-plane magnetic recording that a magnetic field generated from the magnetic domain boundaries hinders formation of minute magnetic domains, high-density recording using a thick magnetic film becomes possible. In addition, the thermal fluctuation of magnetization is suppressed by the thick magnetic film. In this way, there is a possibility of realizing a recording density that cannot be obtained by in-plane magnetic recording, and in fact, experiments of a linear recording density exceeding 300 kFCI (Flux Change per Inch, the number of magnetization reversals per inch) have been performed. is there.

However, in perpendicular magnetic recording, there is a problem that the medium noise is large, which is a factor that hinders practical use. The noise is compared with the magnitude of the reproduced output signal, and is usually evaluated by a signal-to-noise ratio. Each time the magnetic head crosses the recording magnetization reversal region, the reproduction output signal is generated as a voltage peak on the plus side and the minus side with respect to the output (zero level) in the zero magnetic field state. This voltage peak is defined as S (Vp-p), and a frequency band from a frequency based on the repetition period of the voltage peak to DC (usually 0).
The mean square value of noise in a band of about 100 MHz) is defined as N (Vrms), and the ratio S / N is the signal-to-noise ratio (hereinafter, the signal-to-noise ratio is referred to as "S / N").

In perpendicular magnetic recording, for example, when recording is performed at a density of 2 gigabits / square inch, the S / N of the current medium is 23.8 dB, and the S / N is further reduced in higher density recording. [For example, the Journal of Magnetism and Magnetic Materials
tic Materials), Vol. 134, pp. 304-304 (issued in 1994)].

[0006]

The above-mentioned S / N is insufficient for recording and reproducing digital signals, and it is impossible to obtain a magnetic recording / reproducing apparatus which can be put to practical use.

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a high-density perpendicular recording medium capable of ensuring a high S / N, and to provide a magnetic recording / reproducing apparatus using the same. It is in.

[0008]

According to the present invention, there is provided a perpendicular magnetic recording medium comprising: a substrate made of a nonmagnetic material; and a magnetic layer formed on the nonmagnetic substrate. The magnetic layer has a controlled crystal orientation and crystal grain size, and has Pt, Pd, Au, Ag, R
It is characterized in that a noble metal layer made of at least one element selected from the noble metal element group of h, Ir and Ru is formed.

In a magnetic recording apparatus using a magnetic recording medium, the noise includes, in addition to the medium noise, noise of a magnetic head and a reproducing circuit itself for amplifying an output signal of the magnetic head. Become. The present inventor has found that when recording a digital signal as in a magnetic disk drive, the S / N of the magnetic recording medium is required to be at least 26 dB in consideration of the entirety from the analysis results of the allowable error rate. It is clear that.

The S / N ratio of a signal reproduced by a magnetic head when the recording medium is recorded at a density of 10 gigabits per square inch and the ratio of the bit length to the track width is in the range of 1:10 to 1:20. It is given for the frequency band from frequency to direct current.

In order to secure the above S / N, reduction of medium noise is the biggest issue. As a result of examining the recording / reproducing characteristics of the perpendicular magnetic recording medium, it was found that, unlike the in-plane magnetic recording medium, the noise was high even when DC erasure was performed.
Further, as a result of examining the magnetization state of the perpendicular magnetic recording medium with a magnetic force microscope, it was found that even when DC erasing was performed, fluctuations in magnetization existed near the surface, which caused high noise.

The fluctuation of magnetization near the surface is based on a decrease in perpendicular magnetic anisotropy near the surface. One of the causes is that, in the case of a medium formed of an alloy such as Co-Cr, the composition near the surface is different from that inside the film due to the segregation effect. In addition, the unevenness of the surface is one of the causes for reducing the perpendicular magnetic anisotropy near the surface.

To solve this problem, it is desirable that the magnetic film has a high magnetic anisotropy energy. However, when the magnetic anisotropy energy is increased, the magnetic field for recording is increased, which causes a problem that the recording by the recording head becomes difficult.

Therefore, preventing the decrease in the magnetic anisotropy near the surface of the magnetic film while increasing the magnetic energy of the entire magnetic film, or increasing the magnetic anisotropy is a clue for solving the problem. The present invention has been made by finding a clue to solving such a problem. That is, in the present invention, a single noble metal or a noble metal alloy layer is formed on the magnetic film. When the noble metal layer is formed on the magnetic layer and the interface between the magnetic metal and the noble metal is formed, the interface magnetic anisotropy is induced with the direction of easy magnetization in the direction perpendicular to the film surface. It turned out to be obtained. Such interfacial magnetic anisotropy is particularly noticeable when an interface is formed between a magnetic layer of Co or an alloy thereof and a noble metal such as Pt or Pd.

The combination of a magnetic layer and a noble metal is described in Applied Physics Letters, Vol. 47, 178-18, US.
See page 0 (issued in 1985). However, the recording medium of this document has a very thin Co film of about
A multilayer film having a thickness of about 1 μm is formed by alternately stacking Pd films that are extremely thick compared to that of about Å. Since the magnetic film is extremely thin, a magnetic head cannot be used for reproduction. Are different from those of the present invention.

In the present invention, the noble metal layer is formed only on the magnetic film, which will be described in detail later.
It has been found that a high effect of improving magnetic anisotropy can be obtained at nm, and an effect can be obtained at several tens of times. However, the upper limit of the thickness of the noble metal layer is desirably set to approximately 5 nm from a practical viewpoint for the following reasons.

The above-described interface magnetic anisotropy occurs in the magnetic layer near the interface and is not induced in the noble metal layer. Therefore, when the noble metal layer becomes thicker, the distance (spacing) between the magnetic layer and the magnetic head at the time of magnetic recording is increased, and as a result, the reproduction output decreases as the recording wavelength becomes shorter. Results. Further, in a magnetic recording medium, a protective film and a lubricating layer are generally formed on a magnetic layer. These also serve as non-magnetic layers that increase spacing. Since the protective film and the lubricating layer are formed on the noble metal layer also in the recording medium of the present invention,
It was determined that it is appropriate to set the distance between the magnetic layer and the magnetic head in consideration of those thicknesses and set the upper limit of the thickness of the noble metal layer to approximately 5 nm.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording / reproducing apparatus according to the present invention will be described in more detail with reference to embodiments of the present invention according to several embodiments shown in the drawings.

First, FIG. 1 shows the basic structure of a perpendicular magnetic recording medium used in the magnetic recording / reproducing apparatus of the present invention. In FIG. 1, 1 is a substrate made of a non-magnetic material, 2 is an underlayer formed on the substrate 1, 3 is a magnetic layer for recording information formed on the underlayer 2, and 4 is a magnetic layer. The noble metal layer 5 formed thereon is a protective film formed on the noble metal layer 4, and 6 is a lubricating film formed on the protective film 5.

The substrate 1 serves as a base material of the disk.
In addition to tempered glass, Ni-P plated Al alloy or silicon was selected and used. The underlayer 2 is used for controlling the crystal orientation and the crystal grain size of the magnetic layer 3.
Although a single layer of the alloy was used, two or more layers were formed as necessary. Carbon was used as the protective film 5.

[0021]

<Example 1> A perpendicular magnetic recording medium having a sectional structure shown in FIG. 1 was formed on a 2.5-inch tempered glass substrate 1 by a DC magnetron sputtering method. The target of the sputtering apparatus was 6 inches, the argon gas pressure for discharge was set to 3 / 1,000 Torr, and the power of 1 kW was applied to form each layer.

At a substrate temperature of 250 ° C., 3
A Ti-10at (atomic)% Cr film having a thickness of 0 nm is formed as an underlayer 2, and a Co-19at% Cr-10a is formed thereon as a magnetic layer 3.
A t% Pt film was formed with a thickness of 25 nm. Here, Co-19at%
The Cr-10at% Pt film has a hexagonal dense crystal structure, and when its c-axis is oriented in the direction perpendicular to the film surface, this film becomes a perpendicular magnetization film. The Ti-10 at% Cr film underlayer 2 serves to make the c-axis of the magnetic film perpendicular to the film surface.

Further, a noble metal Pt layer 4 was formed on the magnetic layer 3 at a substrate temperature of about 60.degree. The reason for lowering the substrate temperature in forming the Pt layer 4 is to suppress the mutual diffusion between the magnetic layer 3 and the Pt layer 4 and to form a steep interface. Further, a protective film 5 and a lubricating film 6 made of a carbon film having a thickness of 5 nm were formed thereon.

FIG. 2 shows the change in magnetic anisotropy energy by changing the thickness of the Pt layer 4 formed on the magnetic layer 3 in order to confirm the effect when the Pt layer 4 is formed. From the results, the generated interface magnetic anisotropy energy was estimated. Here, the thickness of the region where the magnetic anisotropy changed near the interface was assumed to be 0.5 nm.

As can be seen from FIG. 2, the interface magnetic anisotropy energy ΔKu is smaller than that of Pt in the region where the Pt layer thickness is 1 nm or less.
It increases rapidly as the thickness of the t layer increases, but shows a saturation tendency at 1 nm or more. The value of ΔKu is 3 at a Pt layer thickness of 1 nm.
600,000 emu / cc, and about 400 at 5 nm.
10,000 emu / cc. These are increases in magnetic anisotropy energy near the magnetic layer surface with respect to the case where the noble metal layer is not provided. The magnetic anisotropy energy of the magnetic layer material is generally 3,000,000 emu from the condition that recording is possible with a magnetic head.
/ Cc or less, and the value further decreases near the surface. Therefore, when the interfacial magnetic anisotropy is added, the magnetic anisotropy energy near the surface of the magnetic layer increases more than twice. .

<Embodiment 2> In this embodiment, under the same manufacturing conditions as in Embodiment 1, first, an underlayer 2 on a substrate 1 and a Co-19at% Cr-10at% Pt film as a magnetic layer 3 having a thickness of 25 nm. And a Co layer 31 was formed to a thickness of 1 nm on the surface. Looking at the entire magnetic film including both layers, the concentration of Co, which is a ferromagnetic element, is high near the surface. On the Co layer 31,
A Pt layer 4 is formed, and a protective film 5 is formed on the Pt layer 4.
A nm-thick carbon film and a lubricating film 6 were formed, and a sample having the structure shown in FIG. 3 was formed.

For such a sample, the interfacial magnetic anisotropy was estimated by the method described above. Also in this case, occurrence of interfacial magnetic anisotropy was confirmed, and the value was about 20% larger in each thickness of the Pt layer 4 than in the case of Example 1 in which the Co layer 31 was not formed. The increase in the interface magnetic anisotropy is because the formation of the Co layer 31 reduces the concentration of the ferromagnetic element near the noble metal interface in the entire magnetic layer (the magnetic layer 3 and the Co layer 31 thereon). This is higher than in the case of Example 1, because the occurrence of interfacial magnetic anisotropy was enhanced.

<Embodiment 3> In this embodiment, a noble metal layer is formed on two magnetic layers having different magnetic properties. As the magnetic layer, first, a Ni-Fe layer 32 having an in-plane magnetization characteristic is formed on the underlayer 2 to a thickness of 200 nm.
Furthermore, Co-19at% Cr-10at% of the same composition as above
A magnetic layer 3 of Pt (hereinafter simply referred to as “Co—Cr—Pt”) is formed with a thickness of 25 nm. In-plane magnetization layer 32
Is provided, the recording magnetization state is more stably maintained.

On the magnetic layer 3, a Pt layer 4 was formed to a thickness of 1 nm, and a carbon film 5 nm thick as a protective film 5 and a lubricating film 6 were formed. Thus, a sample having the structure shown in FIG. In such a sample, the interfacial magnetic anisotropy generated when the thickness of the Pt layer 4 was changed was almost the same as in the case of Example 1.

In each of the above embodiments, the noble metal layer 4 is made of Pt.
But other noble metals Pd, Au, Ag, Rh, Ir, Ru
It was also confirmed that the generation of interfacial magnetic anisotropy was able to be performed when the magnetic layer was used, and the perpendicular magnetic anisotropy near the surface of the magnetic layer could be enhanced.

In each of the above embodiments, the magnetic layer 3
However, even when a Fe-based material is used as the magnetic layer 3, the perpendicular magnetic anisotropy near the surface of the magnetic layer can be enhanced by forming an interface with the noble metal layer 4. Was.

With respect to these magnetic recording media, noise characteristics after DC erasing were evaluated. For measurement, MR head (magneto-resistance effect type head) with a shield interval of 0.2 μm
And the spacing was 30 nm. Table 1 shows the magnitude of the noise after DC erasing in comparison with the case where the Pt layer (2 nm thick) was formed on the magnetic layer and the case where it was not formed.

[0033]

[Table 1]

In the case of a Co—Cr—Pt single layer 3 as the magnetic layer, a Co—Cr—Pt layer is formed on the Co—Cr—Pt layer 3 and a Co—Cr—Pt layer is formed on the Ni—Fe in-plane magnetization layer 32. Regarding the three types in which the layer 3 was formed, Pt was formed on the magnetic layer.
By forming the layer 4, the integrated noise value (0 to 50M
(Accumulation in the frequency range of Hz).

FIG. 5 shows an embodiment of a magnetic recording / reproducing apparatus constructed using the above-described perpendicular magnetic recording medium. In FIG. 5, reference numeral 71 denotes the above-described perpendicular magnetic recording medium. A magnetic head 72 held by a suspension 73 faces the medium 71, and extracts magnetic information as an electric signal. The magnetic head 72 held by the suspension 73 passes through an actuator 74 driven by a voice coil motor 75,
The magnetic recording medium is moved to a predetermined position. The positioning at this time is controlled by a positioning circuit 77.

Further, the electric signal from the magnetic head 72 is
It is guided to the recording and reproducing circuit 76. Interface circuit 78
Relays the input and output of electric signals to and from the recording / reproducing apparatus. The medium 71 is rotated by a motor 79.

The recording and reproduction characteristics of this device were measured.
The S / N of B was confirmed.

[0038]

According to the present invention, the magnetic anisotropy near the surface of the magnetic layer of the magnetic recording medium to be used can be increased as compared with the prior art, so that the magnetic recording medium having a high S / N even at a high recording density. A playback device can be configured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a perpendicular magnetic recording medium for explaining a magnetic recording / reproducing apparatus according to the present invention.

FIG. 2 is a curve diagram for explaining the relationship between the thickness of a Pt layer formed on a magnetic layer and interface magnetic anisotropy.

FIG. 3 is a cross-sectional view of a perpendicular magnetic recording medium for explaining a second embodiment of the present invention.

FIG. 4 is a sectional view of a perpendicular magnetic recording medium for explaining a third embodiment of the present invention.

FIG. 5 is a structural diagram for explaining the magnetic recording / reproducing apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Non-magnetic substrate, 2 ... Underlayer, 3 ... Magnetic layer, 31 ... Layer with high ferromagnetic element concentration, 32 ... In-plane magnetization layer, 4 ... Noble metal layer, 5 ... Protective layer, 6 ... Lubricating layer, 71 ... Magnetic recording medium, 7
2: magnetic head, 73: suspension, 74: actuator, 75: voice coil motor, 76: recording / reproducing circuit, 77: positioning circuit, 78: interface control circuit

Continuing on the front page (72) Inventor Nobuyuki Inaba 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-4-67315 (JP, A) JP-A-11-296833 (JP, A) JP-A-61-199241 (JP, A) (58) Fields investigated (Int. Cl. ^7, DB name) G11B 5/64 - 5/667 G11B 5/72

Claims (4)

(57) [Claims] 1. A magnetic recording / reproducing apparatus for performing recording on a perpendicular magnetic recording medium, wherein the perpendicular magnetic recording medium includes a substrate made of a nonmagnetic material and a magnetic layer formed on the nonmagnetic substrate. The magnetic layer has a controlled crystal orientation and crystal grain size, and a Co layer is formed on its surface.
And Pt, Pd, Au, Ag, Rh,
A magnetic recording / reproducing apparatus comprising a noble metal layer formed of at least one element selected from a noble metal element group of Ir and Ru. 2. A magnetic recording / reproducing apparatus for performing recording on a perpendicular magnetic recording medium, wherein the perpendicular magnetic recording medium is formed on a substrate made of a nonmagnetic material and on the nonmagnetic substrate.
A Ni-Fe layer having in-plane magnetization characteristics;
; And a perpendicular magnetization magnetic layer formed above the vertical magnetic
The magnetic layer has a controlled crystal orientation and crystal grain size, and further has Pt, Pd, Au, Ag, Rh, Ir,
Precious metal layer comprising at least one element selected from the noble element group of Ru is formed, further, the noble metal layer
Is a magnetic recording / reproducing apparatus having a thickness of 1 nm or more and 5 nm or less . 3. A substrate comprising a nonmagnetic material and a magnetic layer formed on the nonmagnetic substrate, wherein the magnetic layer comprises:
The table be one crystal orientation and crystal grain size is controlled
A Co layer is formed on the surface, and Pt, P
A perpendicular magnetic recording medium comprising a noble metal layer made of at least one element selected from the group consisting of noble metal elements of d, Au, Ag, Rh, Ir, and Ru. 4. A substrate made of a nonmagnetic material, and a Ni—Fe layer formed on the nonmagnetic substrate and having in-plane magnetization characteristics.
And a perpendicular magnetic layer formed on the Ni-Fe layer , wherein the perpendicular magnetic layer has a controlled crystal orientation and crystal grain size, and has Pt, Pd,
A noble metal layer made of at least one element selected from the noble metal element group of Au, Ag, Rh, Ir, and Ru is formed, and the noble metal layer has a thickness of 1 nm or more and 5 nm.
A perpendicular magnetic recording medium characterized by the following .