JP2993927B2 - Perpendicular magnetic recording medium and magnetic storage device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perpendicular magnetic recording medium and a magnetic storage device which are suitable for high-density magnetic recording and have low reproduction noise and excellent stability of recording magnetization.

[0002]

2. Description of the Related Art Currently, practically used magnetic recording systems include an N-pole and an N-pole, which are parallel to the surface of a magnetic recording medium and are magnetic poles.
This is an in-plane magnetic recording system in which magnetic recording is performed by magnetizing the poles, the S pole, and the S pole in a direction in which they face each other. In order to improve the linear recording density in in-plane magnetic recording, the product of the residual magnetization (Br) and the magnetic film thickness (t) of the magnetic film as a recording medium is reduced to reduce the effect of the demagnetizing field during recording. , It is necessary to increase the coercive force. In addition, in order to reduce medium noise generated from magnetization transition, it is necessary to orient the easy axis of the magnetic film parallel to the substrate surface and control the crystal grain size.
In order to control the crystal orientation and grain size of the magnetic thin film, an underlayer for structure control is formed between the substrate and the magnetic film.

As a magnetic film of the longitudinal magnetic recording system, Co is used.
As the main components, and Cr, Ta, Pt, Rh, Pd,
A Co alloy thin film to which Ti, Ni, Nb, Hf or the like is added is used. As the Co alloy constituting the magnetic thin film, a material having a hexagonal close-packed lattice structure (hereinafter, referred to as an hcp structure) is mainly used. The c axis of the crystal has an easy axis in the <00.1> direction, and the easy axis is oriented in the in-plane direction. In order to control the crystal orientation and grain size of the magnetic thin film, an underlayer for structure control is formed between the substrate and the magnetic film. The underlying layer is mainly composed of Cr, and Ti, Mo, V, W,
A material to which Pt, Pd, or the like is added is used. The magnetic thin film is formed by a vacuum evaporation method or a sputtering method.

As described above, in order to reduce medium noise and improve linear recording density in longitudinal magnetic recording, it is necessary to reduce the product of the residual magnetization (Br) of the magnetic film and the magnetic film thickness (t). For this purpose, it has been studied to reduce the thickness of the magnetic film to 20 nm or less and to refine crystal grains. However, in such a medium in which the magnetic crystal grains are made fine, there is a very serious problem that the recording magnetization decreases due to thermal fluctuation, which is an obstacle to high-density recording.

On the other hand, the perpendicular magnetic recording system is a system in which adjacent recording bits form a magnetic domain in a direction perpendicular to the surface of the recording medium and are antiparallel to each other for recording. There is an advantage that the higher the recording density, the more easily the magnetization can be stably maintained, and this is one of the powerful means of high density magnetic recording.

For high-density recording by in-plane recording, the thickness of the magnetic film needs to be 20 nm or less as described above. In this case, there is a problem that the recording magnetization is lost due to thermal fluctuation. On the other hand, perpendicular recording has the advantage that the magnetic film thickness can be made thicker than in-plane recording, and the recording magnetization can be stably maintained. In order to improve the linear recording density by perpendicular recording, it is necessary to reduce the medium noise generated from the magnetic domain having an irregular structure formed inside the recording bit and at the magnetization transition. For this purpose, it is necessary to align the axis of easy magnetization of the magnetic film perpendicular to the substrate surface, reduce the orientation dispersion of the axis of easy magnetization, and control the crystal grain size.

As the magnetic film of the perpendicular magnetic recording system, Co is used.
As the main components, and Cr, Ta, Pt, Rh, Pd,
A Co alloy thin film to which Ti, Ni, Nb, Hf or the like is added is used. As the Co alloy constituting the magnetic thin film, a material having an hcp structure is mainly used. The Co alloy thin film has an easy axis of magnetization in the c-axis <00.1> direction of the crystal, and orients the easy axis of magnetization in the vertical direction. The magnetic thin film is formed by a vacuum evaporation method or a sputtering method. In order to improve the linear recording density and reproducing output when performing magnetic recording, and to reduce reproducing noise to improve the magnetic recording characteristics, it is necessary to improve the c-axis perpendicular orientation of the Co alloy thin film and to improve the crystal grain size. It is necessary to control the diameter, and for this purpose, improvement measures such as forming an underlayer for structure control between the substrate and the magnetic film have been conventionally taken.

[0008]

[SUMMARY OF THE INVENTION In the perpendicular magnetic recording system few Gb / in ² or more, particularly to achieve a 10Gb / in ² or more ultra-high density magnetic recording, in addition to the reproduction signal to improve the linear recording density It is important to reduce included noise, particularly medium noise caused by the fine structure of the medium. For this purpose, in addition to the crystal orientation of the magnetic thin film, more advanced control of the thin film structure is required. To reduce media noise, for example, Journa
l of The Magnetic Society of Japan Vol.21, Supplem
ent, No.S2 (1997) "Proceeding of The Fourth Perpend
Various improvements have been attempted in the past, as described in the icular Magnetic Recording Conference '97. For example, (1) Non-magnetic Cr in a CoCr-based alloy in order to reduce magnetic interaction between magnetic particles (2) a method of isolating magnetic particles morphologically by controlling the sputtering gas pressure, etc. Improvement of the medium structure promotes reduction of medium noise. However, the effect of reducing the reverse magnetic domain formed in the direction opposite to the magnetization direction, or the magnetic domain inclined with respect to the magnetization direction and the irregular magnetic domain associated therewith, which is the origin of medium noise in perpendicular magnetic recording, is as follows. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art, to have excellent low noise characteristics and stable recording magnetization, and to make perpendicular magnetic recording suitable for ultra-high density magnetic recording. To provide a medium and a magnetic storage device.

[0009]

The relationship between the irregular magnetic domain and the reproduced signal will be described. FIG. 6 is a schematic cross-sectional view showing the magnetization state of a medium on which perpendicular magnetic recording has been performed, and a schematic diagram of a reproduction signal waveform obtained by reproducing the medium with a magnetoresistive head (MR head). FIG. 6A shows a case where ideal perpendicular magnetic recording is performed, and FIG. 6B shows a case where irregular magnetic domains are formed on the recording medium.

As shown in FIG. 6A, when ideal perpendicular magnetic recording is performed, adjacent magnetic domains act at the boundary portion (magnetization transition region) 32 of the recording magnetic domains so as to cancel each other's demagnetizing fields. Therefore, a large magnetization 33 is formed. On the other hand, inside the magnetic domain, the magnetization 33 becomes small due to the influence of the demagnetizing field. In perpendicular magnetic recording, the higher the density, the closer the adjacent recording bits are, and the more the recording bit acts to cancel the demagnetizing field, so that the magnetization is stabilized. As described above, when ideal perpendicular magnetic recording is performed, the magnetizations 33 in the same recording magnetic domain are formed in the same direction, so that a signal having no noise in the reproduction signal waveform 31 can be obtained. However, in reality, the reproduced signal waveform 31 shown in FIG.
As shown in (1), the reproduced signal is disturbed by noise generated from the medium. The causes of medium noise in perpendicular magnetic recording are caused by fluctuations of boundaries (magnetization transitions) 32 of recording magnetic domains and by irregular magnetic domains formed inside the recording magnetic domains. The fluctuation of the magnetization transition is also related to the formation of irregular magnetic domains. As shown in FIG. 6 (b), the irregular magnetic domains that cause the medium noise include the reverse magnetic domains 37 having the magnetization opposite to the average magnetization direction due to the effect of the demagnetizing field acting on the medium. There is a case where the magnetization direction is the same as that due to the formation of a region having the magnetization 38 in which the direction of the magnetization is the same but the direction of the microscopic magnetization is inclined. Either of these causes a fluctuation in the amplitude of the reproduced signal detected on the medium surface, and these are collectively called noise.

In the present invention, by controlling the perpendicular magnetic anisotropy and the crystal orientation of the perpendicular magnetization film formed on the substrate, a magnetic film composed of crystal grains having a large magnetic anisotropy is formed on the substrate. The easy axis of the magnetic crystal grains is highly oriented in the direction perpendicular to the substrate surface, and the dispersion of magnetic anisotropy is particularly reduced to reduce the magnetic domains of the irregular structure formed on the medium surface when magnetic recording is performed, or the magnetic domain structure The above object is achieved by miniaturization of.

That is, in the perpendicular magnetic recording medium according to the present invention, in a perpendicular magnetic recording medium in which the axis of easy magnetization of a magnetic thin film formed on a substrate is oriented in a direction substantially perpendicular to the substrate surface, the perpendicular magnetic recording state or almost perpendicular to the film surface. The average area of the irregular magnetic domains is 7.1 × 10 ⁻⁴ μm ² or less in a remanent magnetization state magnetized in one direction in the vertical direction.

In the present specification, the irregular magnetic domain refers to a region having a direction opposite to the direction of magnetization in a predetermined magnetization region or a direction inclined with respect to the predetermined direction of magnetization. For example, when using a magnetic force microscope that detects a magnetic force gradient between a magnetic probe and a magnetic sample,
The irregular magnetic domains are observed as light-dark contrast. In a region such as a reverse magnetic domain, a large magnetic force gradient is generated and observed as a strong contrast. On the other hand, in a region where the direction of magnetization is antiparallel and the direction of the magnetization is inclined at least 5 degrees or more, the contrast is observed as weaker than the former. You. In a region where the magnetization direction is the same and the magnetization direction is inclined at least 5 degrees or more, the contrast of the magnetic force gradient image becomes strong. At the time of observation with a magnetic force microscope, the average distance between the probe samples was set to 50 to 20 nm, and a threshold was set to 50% of the observed intensity profile of the irregular magnetic domain.
The size at this time defined the size of the irregular magnetic domain. When a spin-polarized scanning electron microscope is used, a bright and dark contrast image is obtained in the upward or downward spin direction, and the inclined magnetic domain region is observed as an intermediate contrast (gray). In this case, the inclination of the magnetization can be detected in the range of 2 to 90 degrees by changing the detection angle of the spin.

The average area of the irregular magnetic domain means the area of the irregular magnetic domain which is sequentially integrated from the smaller one to the larger one, and the integrated intensity ratio expressed as a ratio to the integrated value of the area of all the random magnetic domains. Means 50% area. The area of the irregular magnetic domain included in a range of ± 45% from the average area is 7.8.
It is preferably from × 10 ^{−5 to} 2.8 × 10 ⁻³ μm ² .

The average diameter of the magnetic domain obtained by converting the irregular magnetic domain into a circle having the same area as the irregular magnetic domain is 3
0 nm or less, and the distribution range of the diameter of the magnetic domain is 10 to
Preferably it is 60 nm. Further, it is preferable that the area ratio of the irregular magnetic domain formed in the unit surface area in a remanent magnetization state magnetized in a direction substantially perpendicular to the film surface or in a state of DC demagnetization by the magnetic head is 10% or less.

A magnetic storage device according to the present invention comprises a perpendicular magnetic recording medium, a holder for holding the perpendicular magnetic recording medium, a magnetic head for recording and reproducing information on the perpendicular magnetic recording medium, and a magnetic head. And a moving means for moving the relative position of the perpendicular magnetic recording medium, wherein the perpendicular magnetic recording medium according to the present invention is used as the perpendicular magnetic recording medium.

The evaluation of the magnetization state of the perpendicular magnetic recording medium, that is, the evaluation of the structure of the irregular magnetic domains formed in the perpendicular magnetic recording medium can be performed by any of the following means. A method of detecting the intensity of the stray magnetic field or the stray magnetic field gradient on the surface of the perpendicular magnetic recording medium by a magnetic force microscope [for example, Ruger, et al., "Magnetic force microscopy: Ge
neral principle and application to longitudinal re
cording media "J. Appl. Phys., 68 (3), pp.1169-1183
(See (1990))

Spin SEM (spin-polarized scannin)
g electron microscope) to detect the direction of spin on the surface of the perpendicular magnetic recording medium: [for example, H. Matsu
yama, et al., "High Spatial-Resolution Domain-Obser
vation of Longitudinal ThinFilm Media by Spin-Pola
rized Scanning Electron Microscopy "IEEE Trans.Mag
n., Vol. 30, pp. 1327-1330 (1994))

A method in which magnetic fine particles are adhered to the surface of a perpendicular magnetic recording medium and observed (bitter method):
Sakurai, et al., "Magnetic recording pattern of o
bliquely evaporated Co-O thin films observed by us
ing ultrafine Co particles "J. Appl. Phys., 76, pp.
3177-3180 (1994)] A method for detecting the magnitude of the polarization angle using a polarization microscope:
[For example, Satoshi Chikano "Physics of ferromagnetic material (bottom)" Shokabo,
See pages 156-158]

According to the present invention, by controlling the initial growth layer of the magnetic film formed on the substrate and orienting the easy axis of magnetization in the direction perpendicular to the substrate surface, the magnetic crystal grains can be made finer and more uniform, thereby achieving the medium. The fluctuation structure of the magnetization transition of the recording magnetic domain that causes noise is small, and the miniaturization of the irregular magnetic domain due to the demagnetizing field acting on the magnetic film can be promoted. As a result, the medium noise is reduced and the recording magnetization stability is secured. Therefore, a perpendicular magnetic recording medium suitable for high-density magnetic recording and a magnetic storage device using the same can be realized.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a main part of an example of a magnetic storage device according to the present invention. This magnetic storage device includes a magnetic disk 1, a magnetic head 2 for recording and reproduction, a suspension 3 supporting the magnetic head, an actuator 4, a voice coil motor 5, a recording and reproduction circuit 6, a positioning circuit 7, an interface control circuit 8, and the like. This is a device having a known configuration. The relative position of the magnetic head 2 with respect to the magnetic disk 1 is controlled by an actuator 4 and a voice coil motor 5. The recording / reproducing circuit 6 controls the magnetic head 2 to control a recording signal and detect and amplify a reproduction signal. The positioning circuit 7 is a circuit for controlling the track position for recording and reproducing by the magnetic head, and the interface circuit 8 is a circuit for connecting the reproducing circuit, the positioning circuit and the like to the computer main body.

The magnetic disk 1 has an underlayer for structure control such as crystal orientation of a magnetic film formed on a disk-shaped substrate such as a glass substrate, a Si substrate, an NiP-coated aluminum substrate, and a carbon substrate. This is a magnetic recording medium in which a magnetic film and a protective film are formed, and a lubricating film is coated on the protective film. The magnetic film contains Co as a main component and contains Cr, Fe,
Mo, V, Ta, Pt, B, Ir, W, Hf, Nb, R
at least one selected from u, Ni and rare earth elements
A hexagonal close-packed structure made of a material containing various kinds of elements is used as a basic structure, and the axis of easy magnetization of the magnetic film is oriented in a direction perpendicular to the substrate surface. The easy axis of magnetization of the magnetic film is highly oriented perpendicular to the substrate surface,
In addition, in order to obtain a perpendicular recording medium having small dispersion of perpendicular magnetic anisotropy, an underlayer for controlling the structure of the magnetic film is provided between the substrate and the magnetic film. As the underlayer for controlling the structure, a nonmagnetic or paramagnetic CoCr alloy, Ti, TiCr alloy, or Pt, Ru, Ta, Mo, Pd, V, Nb, Z
An hcp structure polycrystalline film, microcrystalline film, amorphous underlayer film, or amorphous underlayer such as Si or Ge to which r is added is used.

The magnetic head 2 comprises a magnetic pole of a magnetic recording ring type head provided on a slider and a magnetoresistive, giant magnetoresistive, spin valve or magnetic tunnel type element for reproducing a recorded signal. Is done. The gap length of the magnetic head for reproducing the recording signal is 0.25 μm or less, preferably 0.1 to 0.2 μm in order to obtain a high-resolution reproduction signal. In order to reduce the disturbance of the recording magnetic domain at the end of the track at the time of magnetic recording, it is desirable that both ends of the track on the trailing and leading poles of the recording head are aligned, and to generate a steep recording magnetic field. The gap length of the recording head is 0.25 μm or less, preferably 0.1 to 0.2 μm. Making the track width of the reproducing head narrower than the track width of the magnetic pole of the recording head is effective in reducing reproduction noise generated from both ends of the recording track. The magnetic head 2 is supported by the suspension 3 and has a function of correcting a yaw angle generated when the magnetic head moves from the inner circumference to the outer circumference of the magnetic disk.

The perpendicular magnetic recording medium according to the present invention will be described in more detail with reference to the schematic sectional view shown in FIG. FIG.
2A is a schematic sectional view of a perpendicular magnetic recording medium having two underlayers, and FIG. 2B is a schematic sectional view of a comparative perpendicular magnetic recording medium having one underlayer. As the substrate, Si substrate, glass substrate, NiP coated Al substrate, carbon substrate,
Alternatively, a polymer substrate or the like can be used. Here, an example in which a disk-shaped Si disk having a thermally oxidized Si film formed on the surface as the substrate 11 will be described. In the present embodiment, a medium was manufactured using an ultra-high vacuum DC magnetron sputtering device. The cleaned substrate 11 was set in a sputtering apparatus, and subsequently, the substrate 11 was heated to about 230 ° C. to form an underlayer 12 (13) for controlling the crystal grain size and magnetic anisotropy of the magnetic film. . The underlayer can be arbitrarily selected according to the type of the magnetic film 14 formed thereon, and the underlayer can be formed by laminating one or more layers made of the same material or different materials.

As the magnetic film 14, a material having an hcp structure, a body-centered cubic lattice structure, a face-centered hexagonal lattice structure, or an orthorhombic structure can be used. For example, as a magnetic film, Co
When a material having an hcp structure whose main component is Hc is used, the underlayer 12 (13) is most commonly formed of hcp such as Ti, Co, or the like.
Cr-, V-, W-, T-
a, Ru, Hf, etc., a polycrystalline film, microcrystalline film, amorphous film, Si, Ge, T
a, an amorphous film such as Hf can be selected, and a non-magnetic material is preferable. On this underlayer, a magnetic film 14 and a protective film 15 to be a recording film were successively formed in the same vacuum.

As described below, the perpendicular magnetic recording media A, B, and B having two underlayers as schematically shown in FIG.
C, D, E, and F were produced. Media A, B, C, D, E,
All the thin films in F were produced by an ultrahigh vacuum DC magnetron sputtering method at an Ar gas pressure of 2 mTorr. In any medium, the thickness of the first underlayer 12 is 30 n.
m, the thickness of the second underlayer 13 was 20 nm, the thickness of the magnetic film 14 was 30 nm, and the thickness of the protective film 15 was 5 nm.

The first underlayer 12 is formed on the second underlayer 12.
It has the effect of controlling the nucleation of the underlayer and promoting the epitaxial growth of the thin film. Here, an example using a Ti-10 at% Cr alloy film will be described. The second underlayer 13 has an effect of promoting the epitaxial growth of the magnetic film 14 formed thereon, and is mainly composed of a material such as Ti or Co.
A thin film made of a non-magnetic or paramagnetic alloy made of a material to which Cr, V, W, Ta, Ru, Hf or the like is added is used. The magnetic film 14 contains Co as a main component,
r, Fe, Mo, V, Ta, Pt, Si, B, Ir,
A material containing at least one element selected from W, Hf, Nb, Ru, Ni and a rare earth element is used.
Carbon, diamond-like carbon,
Alternatively, a carbide film or a nitride film of Si, Ta, Ti, Hf or the like can be used. Here, an example using carbon will be described. Also, here, an example in which the magnetic film is formed on one side of the substrate will be described, but it goes without saying that the magnetic film may be formed on both sides of the substrate.

The medium A is made of Ti-10a as a first underlayer.
Co-35a as a second underlayer using a t% Cr alloy film
An hcp structure thin film made of a t% Cr-2at% Ta alloy thin film was used. As the magnetic film 14, Co-19 at% C
An r-10 at% Pt alloy was used. Carbon was used for the protective film 15. In the medium B, the first underlayer 12, the second underlayer 13, and the protective film 15 are made of the same material as the medium A, and the magnetic film 14 is Co-17at% Cr-10at% Pt-.
A 4 at% Ta alloy was used.

The medium C includes a first underlayer 12, a second underlayer 1,
3 and the protective film 15 were made of the same material as that of the medium A, and a Co-15 at% Cr-4 at% Ta alloy was used as the magnetic film 14. In the medium D, the first underlayer 12 and the protective film 15 have the same material configuration as the medium A. Co as the second underlayer 13
A non-magnetic alloy made of a -35 at% Cr alloy was used, and a Co-19 at% Cr-10 at% Pt alloy was used as the magnetic film 14.

The medium E includes a first underlayer 12, a second underlayer 1,
3 and the protective film 15 are made of the same material as the medium D, and the magnetic film 14 is Co-17 at% Cr-10 at% Pt-4.
An at% Ta alloy was used. The medium F includes a first underlayer 12,
The second underlayer 13 and the protective film 15 are made of the same material as the medium D, and the magnetic film 14 is Co-15 at% Cr-4 at.
% Ta alloy was used.

When the surface of the underlayer and the surface of the magnetic film in the media A, B, C, D, E and F were observed by an atomic force microscope (AFM), the amplitude of the surface undulation and the period of the undulation were all 10 nm. The following flat thin film was obtained. Further, the magnetic films in the media A, B, C, D, E, and F have an hcp structure, and the <002> direction of the magnetic film is oriented perpendicular to the substrate surface. The grown thin film was confirmed by an X-ray diffraction method and electron microscope observation.

By adding nonmagnetic Cr or Ta to the magnetic film 14, a nonmagnetic layer or a weak magnetic layer can be locally segregated in the grain boundaries or in the magnetic crystal grains, and the magnetic particles are magnetically isolated. The effect of improving the properties has been confirmed by composition analysis using an electron microscope and the like. By adding Pt, the magnetic anisotropy of the magnetic film can be improved. The multi-layered structure of the underlayer has the effect of promoting the crystal growth of the magnetic film 14 formed thereon, and consequently makes the magnetic crystal grain size uniform, improves magnetic anisotropy, Medium noise can be reduced by reducing the regular magnetic domain diameter. Also, as in the case of the media A, B, and C, the second underlayer 13 is multiplexed into three or more elements, so that the magnetic crystal grain size is 10 to 20 as compared with the media D, E, and F.
%, So that the size of the irregular magnetic domain can be reduced.

Next, as shown in FIG. 2B, a perpendicular magnetic recording medium G having a single underlayer
H and I were produced. The thin films in the media G, H, and I were all prepared by an ultrahigh vacuum DC magnetron sputtering method at an Ar gas pressure of 2 mTorr. Both media,
The thickness of the underlayer 12 is 30 nm, and the thickness of the magnetic film 14 is 30.
nm, and the thickness of the protective film 15 was 5 nm. Carbon was used for the protective film 15.

The medium G is a 30 nm-thick h film on the substrate 11.
A microcrystalline first underlayer 12 made of a Ti-10 at% Cr alloy film having a cp structure is formed, a 30 nm-thick magnetic film 14 is formed directly on the first underlayer, and a film thickness is formed thereon. 5
An nm protective film 15 was formed. The magnetic film 14 has Co-1
A 9 at% Cr-10 at% Pt alloy was used. Medium H
Is a 30 nm thick hcp structure Ti-1 on a substrate 11.
Microcrystalline first underlayer 12 of 0 at% Cr alloy film
Was formed thereon, and a 30 nm-thick magnetic film 14 and a 5 nm-thick protective film 15 were formed thereon. The magnetic film 14 has Co
A -17 at% Cr-10 at% Pt-4 at% Ta alloy was used.

The medium I has a thickness of 30 nm on the substrate 11.
A microcrystalline first underlayer 12 made of a Ti-10 at% Cr alloy film having a cp structure was formed, and a 30 nm-thick magnetic film 14 and a 5 nm-thick protective film 15 were formed thereon.
The magnetic film 14 has Co-15 at% Cr-4 at% Ta
An alloy was used. The magnetic films 14 of the media G, H, and I all have the hcp structure, and the <002> direction is oriented almost perpendicular to the substrate surface, and all of them grow almost epitaxially from the underlayer surface. The thin film was confirmed by X-ray diffraction and electron microscope observation. However, a region in which the crystal orientation was slightly disordered was also observed in the initial growth layer at the lower interface. As a result of observing the underlayer surface and the magnetic film surface of the media G, H, and I with an atomic force microscope (AFM), the amplitude of the surface undulation and the period of the undulation were all in the range of 10 to 50 nm.

The magnetic characteristics of the media A to I were measured by a vibrating sample magnetometer (VSM). Perpendicular magnetic anisotropy K of magnetic film
In determining u, a magnetic torque curve is measured for each sample, and the magnetic torque curve per unit volume is subjected to Fourier analysis to obtain a crystal magnetic anisotropy represented by the following approximate expression [Equation 1] [Equation 2]. The uniaxial magnetic anisotropy constants Ku ₁ , K in the direction perpendicular to the film surface of the magnetic film
I was asked to u _2. Here, Ku ₁ , Ku ₂ , Ku ₃ : uniaxial anisotropy constant, θ: angle between spontaneous magnetization and easy axis of the magnetic film, M
s: saturation magnetization.

[0037]

E ≒ Ku ₁ sin ² θ + Ku ₂ sin ⁴ θ + Ku ₃ sin ⁶ θ

[0038]

L = − (Ku ₁ + Ku ₂ −2πMs ² ) sin 2θ
+ (Ku ₂ sin4θ) / 2

In order to more accurately determine the values of Ku ₁ and Ku ₂ , the magnitude of the external magnetic field H applied to the magnetic film in the measurement of the magnetic torque curve was measured by changing the magnitude in the range of 15 to 5 kOe. The values of the uniaxial magnetic anisotropy constants Ku ₁ and Ku ₂ measured under the applied magnetic field H and the reciprocal of the applied magnetic field (1/1)
H) was determined. That is, the value of Ku ₁ , Ku ₂ versus 1
In the plot showing the relationship of / H, the value obtained by extrapolating to 1 / H = 0 was defined as the value of Ku ₁ and Ku ₂ of each magnetic film. The magnetic anisotropy Ku in the direction perpendicular to the film surface is K
Defined as u = Ku ₁ + Ku ₂ and approximated.

Table 1 shows the characteristics of the perpendicular magnetic recording media A to I in comparison. In Table 1, Δθ ₅₀ is an index indicating the crystal orientation of the magnetic film, and is the half width of the rocking curve of <002> X-ray diffraction. Ms is the saturation magnetization, Mr
Is the residual magnetization, and Hc is the coercive force in the direction perpendicular to the film surface.

[0041]

[Table 1]

A ring type magnetic head (track width 2 μm, gap length 0.2 μm) is used for magnetic recording, and a magnetoresistive head (MR head, gap length 0.1 μm) is used for reproduction.
Magnetic spacing (distance between the surface of the medium magnetic film and the magnetic pole of the magnetic head) at the time of recording / reproducing 30 nm
The recording and reproduction characteristics of the medium were measured. In Table 1, the medium noise N / S ₀ is a linear recording density of 250 kFCI.
The noise measured in (1) was displayed as a value normalized by the reproduced signal output at a low linear recording density (5 kFCI).

The magnetized state of the magnetically recorded sample and the remanent magnetization state were observed, and the structure and size of the irregular magnetic domain that caused medium noise were evaluated. Here, evaluation was performed by magnetic force microscope (MFM) observation, but other observation means, such as a means for detecting the direction of spin on the surface of the perpendicular magnetic recording medium, or a means for detecting the magnitude of the polarization angle, Alternatively, the evaluation can be performed by using a means for detecting the intensity of the leakage magnetic field or the gradient of the leakage magnetic field on the surface of the perpendicular magnetic recording medium, a means for attaching magnetic fine particles to the surface of the perpendicular magnetic recording medium and evaluating the same.

In Table 1, the area and diameter of the irregular magnetic domain are values obtained from FIGS. FIG. 3 shows a comparison between the magnetization states of the medium A and the medium G. FIG. 3A is a magnetic force microscope image showing the magnetization state of the medium A, and FIG. 5 is a magnetic force microscope image showing the above. In the figure,
The white region 21 is a region having magnetization in the magnetization direction, while the black region 22 is an irregular magnetic domain having a magnetization region having a magnetization opposite to the magnetization direction or having a magnetization inclined with respect to the magnetization direction. Represents. The smaller the size of these irregular magnetic domains and the smaller the ratio of the irregular magnetic domains per unit area, the more the reproduction noise by the magnetic head can be reduced. As shown in FIG. 3, the magnetization state of each of the above media was observed, and the size (area) of each of the irregular magnetic domains formed in the media was measured. Further, the diameter of the irregular magnetic domain was evaluated by approximating a circle having the same area as the above-mentioned irregular magnetic domain.

FIG. 4 shows the relationship between the size (area, diameter) of the irregular magnetic domains and the integrated intensity ratio of the irregular magnetic domains of each of the media A to I obtained by observing the magnetization state as shown in FIG. In FIG. 4, the integrated intensity ratio is obtained by sequentially integrating the areas of the irregular magnetic domains from a small irregular magnetic domain to a large irregular magnetic domain, and is represented by a ratio of the size (area or diameter) of all the irregular magnetic domains to the integrated value. Was. The integrated intensity ratio of 50% is the average value of the irregular magnetic domains in each medium.

Table 1 also shows the average area and average diameter of the irregular magnetic domains measured based on the results of FIG. Table 1, FIG. 3,
As is clear from the comparison of FIG. 4, it is clear that the smaller the average area of the irregular magnetic domains or the average diameter of the irregular magnetic domains, the more the medium noise can be reduced. In particular, ultra-high density magnetic recording of 10 Gb / in ² or more is realized by setting the average area of the irregular magnetic domains to 7.1 × 10 ⁻⁴ (μm ² ) or less or the average diameter of the irregular magnetic domains to 30 nm or less. 0.01 (μVrms / μV _pp) following low-noise medium is required to be able to obtain.

Usually, the magnetic head is 20 to 6
It is used while traveling in a region separated by 0 nm, and detects a leakage magnetic field generated from the surface of the medium and uses it as a reproduction signal. in this case,
As the magnetic domain on the medium surface is larger, the leakage magnetic field is distributed farther from the medium surface, so that the detection efficiency of the magnetic head becomes higher. That is, a small magnetic domain has a larger spacing loss when reproducing with a magnetic head than a large magnetic domain, and is hard to detect. Therefore, by reducing the irregular magnetic domains formed on the medium surface, the medium noise when detecting signals with the magnetic head can be reduced.

The magnetic crystal grains of the media A to I were observed with a transmission electron microscope and an atomic force microscope, and the average diameter of the magnetic crystals and the average diameter of the irregular magnetic domains were compared. As a result, medium A,
In B and C, the average diameter of the irregular magnetic domain is 1 to 1.8 times the average diameter of the magnetic crystal, in the mediums D, E and F, 1 to 3 times, and in the comparison media G, H and I, 1.2. It was 10 times. Also, M
By setting the ratio of r / Ms to 0.8 or more, it is possible to stably maintain the magnetization recorded magnetically for a long time. Or, even in a DC erased state) or at a low recording density (for example, 5 kFCI), it is possible to keep the reproduction output decay rate one year later based on immediately after recording (one second after recording) to a small value of 20% or less. there were.

FIG. 5 compares the relationship between the medium noise and the diameter and area of the irregular magnetic domain based on the results of FIG. FIG. 4 also shows the distribution of the diameters of the irregular magnetic domains and the distribution of the area of the irregular magnetic domains in which the integrated intensity ratio of the irregular magnetic domains is in the range of 5 to 95% in FIG. As is clear from this figure, when the size (average diameter, average area) of the irregular magnetic domain is reduced, and when the distribution width of the diameter and area of the irregular magnetic domain is reduced, the effect of reducing the medium noise is large. Recognize. In particular, the area of the irregular magnetic domain is 7.8 × 1
0 ^{-5 to} 2.8 × 10 ^-3 μm ² , the diameter of the irregular magnetic domain is 10
By setting the range to 60 nm, the effect of reducing the medium noise is improved. The lower limit in the size distribution of the irregular magnetic domains depends on the particle size of the magnetic particles. If the particle size of the magnetic particles is too small, the stability of recording is reduced due to thermal fluctuation. Therefore, it is preferable that the diameter of the irregular magnetic domain does not become smaller than 10 nm.

As described above in detail, by reducing the size of the irregular magnetic domains on the medium surface, the fluctuation amplitude of the inside of the recording bit or the magnetization transition during magnetic recording can be reduced, and as a result, the medium noise is reduced. However, ultra-high-density magnetic recording with high recording resolution can be realized.

[0051]

According to the present invention, an ultra-high surface recording having a high S / N characteristic of a reproduction signal, in which the fluctuation structure of the magnetization transition of the recording magnetic domain causing the medium noise is small and the irregular magnetic domain is fined. A perpendicular magnetic recording medium and a magnetic storage device suitable for high-density magnetic recording can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a main part of an example of a magnetic storage device according to the present invention.

2A is a schematic cross-sectional view of a perpendicular magnetic recording medium having two underlayers, and FIG. 2B is a schematic cross-sectional view of a comparative perpendicular magnetic recording medium having one underlayer.

3A is a magnetic force microscope image showing a magnetization state of a medium A, and FIG. 3B is a magnetic force microscope image showing a magnetization state of a medium G.

FIG. 4 is a diagram showing the relationship between the size (area, diameter) of an irregular magnetic domain and the integrated intensity ratio of the irregular magnetic domain.

FIG. 5 is a comparison diagram of the relationship between medium noise and the diameter and area of irregular magnetic domains.

FIG. 6 is a schematic cross-sectional view showing a magnetization state of a medium on which perpendicular magnetic recording has been performed, and a schematic diagram of a reproduction signal waveform obtained by reproducing the same with a magnetoresistive head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk, 2 ... Magnetic head, 3 ... Suspension, 4 ... Actuator, 5 ... Voice coil motor, 6
... Recording / reproducing circuit, 7 ... Positioning circuit, 8 ... Interface control circuit, 11 ... Substrate, 12 ... First underlayer, 13 ...
Second underlayer, 14: magnetic film, 15: protective film, 21: magnetization in the magnetization direction, 22: irregular magnetic domain.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaaki Nihon 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-11-185236 (JP, A) JP-A Heisei 11-232633 (JP, A) JP-A-7-176027 (JP, A) JP-A-10-255251 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/66

Claims (5)

(57) [Claims] In a perpendicular magnetic recording medium in which the axis of easy magnetization of a magnetic thin film formed on a substrate is oriented substantially perpendicular to the substrate surface, the magnetic thin film is magnetized in a perpendicular magnetic recording state or in one direction substantially perpendicular to the film surface. A perpendicular magnetic recording medium characterized by having an average area of irregular magnetic domains of 7.1 × 10 ⁻⁴ μm ² or less in a remanent magnetization state. 2. The perpendicular magnetic recording medium according to claim 1, wherein the area of the irregular magnetic domain included in a range of ± 45% from the average area is 7.8 × 10 ^{−5 to} 2.8 × 10. ^-3
μm ² , a perpendicular magnetic recording medium. 3. The perpendicular magnetic recording medium according to claim 1, wherein the average diameter of the magnetic domain obtained by converting the irregular magnetic domain into a circle having the same area as the irregular magnetic domain is 30n.
m or less, and the distribution range of the diameter of the magnetic domain is 10 to 60.
nm. 4. The perpendicular magnetic recording medium according to claim 1, wherein the perpendicular magnetic recording medium is formed in a unit surface area in a remanent magnetization state magnetized in a direction substantially perpendicular to the film surface or in a DC demagnetized state by a magnetic head. A perpendicular magnetic recording medium, wherein the area ratio of the irregular magnetic domains is 10% or less. 5. A perpendicular magnetic recording medium, a holder for holding the perpendicular magnetic recording medium, a magnetic head for recording / reproducing information to / from the perpendicular magnetic recording medium, and the magnetic head and the perpendicular 5. A magnetic storage device comprising: a moving unit for moving a relative position of a magnetic recording medium, wherein the perpendicular magnetic recording medium according to claim 1 is used as the perpendicular magnetic recording medium. Magnetic storage device.