JP2002183928A - Magnetic recording medium and magnetic recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having low noise and high coercive force with respect to a magnetic recording medium having a magnetic multilayered film as a magnetic recording layer in which alloy layers essentially comprising Co and layers essentially comprising Pt or Pd are alternately laminated on a nonmagnetic substrate, and to provide a magnetic recording device having high recording density and low noise using the above magnetic recording medium. SOLUTION: The magnetic recording medium has the magnetic multilayered film as the magnetic recording layer produced by alternately laminating alloy layers essentially comprising Co and layers essentially comprising Pt or Pd on the nonmagnetic substrate. In the M-H curve representing the magnetic characteristics of the magnetic multilayered film in the direction perpendicular to the film plane, the gradient A of the curve at the point of M=0 satisfies 1/4π(emu/cc/Oe)<=A<2×1/4π (emu/cc/Oe). The magnetic recording medium is used for the magnetic recording device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium used for a magnetic recording device such as a magnetic disk device, a floppy (registered trademark) disk device, and a magnetic tape device.

[0002]

2. Description of the Related Art In recent years, the application range of magnetic recording devices such as magnetic disk devices, floppy disk devices, and magnetic tape devices has been remarkably increased, and their importance has been increased. Significant improvement in recording density is being achieved.

[0003] It is essential to reduce noise in order to achieve a higher density of a magnetic recording medium. For this reason, the particles forming the medium are becoming finer and the recording layer is becoming thinner. It has been pointed out that the means for reducing the volume of the magnetic particles causes superparamagnetization of the magnetic particles and impairs the recording stability. The stability of the recording means that the information once recorded can be retained with the lapse of time, and with the recent increase in density, the level of this stability has been reduced to a practically problematic area. There is a problem.

[0004] In order to solve these problems, a recording medium using antiferromagnetic coupling or (EN Abbra et al., 200
0Digests of INTERMAG, AA-0
6) Research on perpendicular magnetic recording media that can increase the magnetic film thickness in principle (S. Iwasaki et al., IEEE Tran)
s. Magn. , MAG-14, 849 (197
8)) is prosperous.

In particular, regarding a magnetic recording layer for a perpendicular recording medium, a crystal lattice made artificially by alternately laminating Co / Pt or Pd, which can realize high perpendicular magnetic anisotropy, from a single atom to several atomic layers. A magnetic recording medium using an artificial lattice magnetic multilayer film having a structure (hereinafter, simply referred to as a magnetic multilayer film) has attracted attention as a next-generation medium (Japanese Patent No. 30422878).

[0006]

In a magnetic multilayer film in which an alloy layer mainly containing Co and a layer mainly containing Pt or Pd are alternately laminated, an alloy layer mainly containing Co and Pt or Pd It is known that magnetic anisotropy is induced in the direction perpendicular to the film surface at the interface of the layer mainly composed of, and this magnetic multilayer film exhibits magnetic anisotropy perpendicular to the film surface (P.
F. Carcia; Vac. Sci. Techno
l. A5 (4), July / Aug. 1987). Therefore, the alloy layer containing Co as a main component and Pt or Pd
Attention has been paid to the possibility of a magnetic recording medium using, as a magnetic recording layer, a magnetic multilayer film in which layers mainly composed of are alternately stacked.

However, a magnetic recording medium using this magnetic multilayer film as a magnetic recording layer has the advantage that the recording stability can be increased due to the high coercive force, but the noise tends to be large and the magnetic recording medium is still ready for practical use. This is not the case. In a magnetic multilayer film in which an alloy layer containing Co as a main component and a layer containing Pt or Pd as a main component are alternately laminated, at the interface between the alloy layer containing Co as a main component and the layer containing Pt or Pd as a main component, Magnetic anisotropy is induced in a direction perpendicular to the film surface. In many cases, strong exchange coupling works between crystal grains in the film. When such a film is used as a magnetic recording layer, when a small portion of the film is magnetized for recording reversal, the region where the exchange coupling of the crystal grains in the portion is too strong and the magnetization reversal is performed from a predetermined region. Deviated, that is, due to strong exchange coupling between crystal grains, the magnetization of the crystal grains outside the area to be inverted is dragged and inverted, or the crystal grains in the area to be inverted are inverted by the exchange coupling force of the outside crystal grains Some phenomena may not be possible. Such incomplete magnetization reversal at the time of magnetic recording is not preferable because it causes a phenomenon of noise of a recording signal.

Conventionally, in order to reduce exchange coupling between crystal grains, there has been an example in which the Ar gas pressure during sputter deposition is increased (K. Ouchi et al., J. Mag.).
n. oc. Japan, 21, p301 (199
7)), the effect was not enough. The present invention solves the above conventional problems, has low noise and high coercive force,
An object of the present invention is to provide a magnetic recording medium having excellent recording and reproducing characteristics.

[0009]

Such a magnetic multilayer film in which the exchange coupling between crystal grains is very strong is usually perpendicular to the film surface with almost no inclination of the MH curve. ing. The inventor weakened the exchange coupling between crystal grains of the magnetic multilayer film so as to be suitable for magnetic recording, and inclined the MH curve perpendicular to the film surface of the magnetic multilayer film to a specific range. It was found out that the magnetic recording characteristics of the magnetic multilayer film were improved by the above, and the present invention was reached.

That is, the gist of the present invention is that a non-magnetic substrate
An alloy layer containing Co as a main component;
Alternatively, a magnetic recording medium having a magnetic multilayer film in which layers containing Pd as a main component are alternately stacked, wherein M = 0 of an MH curve representing a magnetic characteristic in a direction perpendicular to the film surface of the magnetic multilayer film. A magnetic recording medium characterized in that a slope A at a point satisfies the following expression, and a magnetic recording device using the magnetic recording medium.

1 / 4π (emu / cc / Oe) ≦ A <2
× １ ／ π (emu / cc / Oe) With the magnetic recording medium of the present invention, a magnetic recording medium having low noise and high coercive force can be realized by having the above characteristics.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the magnetic recording medium of the present invention, an alloy layer mainly composed of Co and a layer mainly composed of Pt or Pd are alternately laminated as a magnetic recording layer on a non-magnetic substrate. A magnetic recording medium having a magnetic multilayer film according to claim 1, wherein a slope A at a point of M = 0 of an MH curve representing a magnetic characteristic in a direction perpendicular to a film surface of the magnetic multilayer film satisfies the following expression. It is characterized by the following.

1 / 4π (emu / cc / Oe) ≦ A <2
× １ ／ π (emu / cc / Oe) Here, a VSM (vibrating sample magnetometer) or the like is usually used for measuring the MH curve. The MH curve refers to a magnetization M (emu / mag) generated when a magnetic field H (Oe) is applied to a medium.
cc) are plotted on the X and Y axes, respectively (FIG. 1). On this graph, a tangent is drawn at the intersection of M = 0, that is, the X axis, and the inclination of the tangent is represented by A (emu).
/ Cc / Oe). Here, it is assumed that the MH curve is not subjected to the demagnetizing field correction.

The inclination of the MH loop is 2 × １ ／ π (e
If it is larger than (mu / cc / Oe), disturbance of recording magnetization transition becomes large when magnetic recording is performed on the magnetic multilayer film, and the medium becomes large in transition noise. When the inclination of the MH loop is smaller than 1 / 4π, it indicates that the medium has a small exchange coupling between the particles and a large dispersion of the coercive force. Recording / reproducing characteristics deteriorate. The slope A of this MH curve is
More preferably, 1.5 × １ ／ π (emu / cc / O
e) below.

In the present invention, the MH loop is tilted by a predetermined amount to be suitable for magnetic recording, because Ta, Nb, W, Ge, C, C
This can be achieved by adding additional elements such as r and B. This is because these additional elements are segregated at the grain boundaries of the Co magnetic crystal grains in the alloy layer containing Co as a main component, and the exchange coupling between the Co magnetic crystal grains is controlled to a predetermined strength. . Here, the Co content in the alloy layer containing Co as a main component is preferably 50 atomic% or more, more preferably 60 atomic% or more. Further, in the alloy layer containing Co as a main component, the above Ta, Nb, W, Ge, C, C
A trace element other than the additional elements such as r and B may contain about several atomic%.

The effect is particularly great when both Cr and B are simultaneously contained. The amounts of Cr and B contained are preferably at least 10 atomic% of Cr and at least 1 atomic% of B,
More preferably, it is at least 15 atomic% of Cr and at least 5 atomic% of B. If the contents of Cr and B are too small, the segregation amounts of Cr and B at the crystal grain boundaries are small, and the exchange coupling between crystal grains may not be sufficiently reduced. The contents of Cr and B are preferably set to 25 atomic% or less of Cr and 10 atomic% or less of B. If the contents of Cr and B are too large,
The perpendicular magnetic anisotropy induced at the interface between the alloy layer containing Co as the main component and the alloy layer containing Pt or Pd as the main component in the magnetic multilayer film may deteriorate.

The layer mainly composed of Pt or Pd has T
a, Nb, W, Ge, C, Cr, B, etc.
It may be contained in a trace amount. The alloy layer containing Pt or Pd as a main component preferably contains Pt or Pd in an amount of 50 atomic% or more.
Atomic% or more. In order to achieve a magnetic multilayer film having the characteristics of the present invention, it is preferable that the substrate temperature at which the magnetic multilayer film is formed by sputtering be 200 ° C. or higher. A more preferred substrate temperature is 250 ° C. By heating the substrate temperature to a predetermined temperature, C
The segregation of r and B is promoted, and the effect of the invention may be further enhanced. The substrate temperature is preferably 500 ° C. or less. If the substrate temperature is too high, an alloy layer containing Co as a main component and Pt
Alternatively, layers containing Pd as a main component may diffuse with each other and be partially integrated to form a clear multilayer film structure. In addition, the crystal grains in the film become large, and the magnetic characteristics may deteriorate. Ar is usually used as a sputtering gas when the magnetic multilayer film is formed, but a rare gas such as Kr or Xe or a mixture thereof may be used, and an impurity gas having a partial pressure of about several percent is added. It does not matter.

The thickness of one alloy layer containing Co as a main component is preferably 0.8 nm or more and 1.5 nm or less. When the film thickness is less than 0.8 nm, the magnetic properties of the magnetic multilayer film, particularly, the coercive force may be deteriorated. If the thickness is larger than 1.5 nm, the magnetic multilayer may have poor magnetic anisotropy in the vertical direction. The thickness of the layer containing Pt or Pd as a main component is preferably from 0.1 nm to 2.0 nm, more preferably from 0.2 nm to 0.8 nm.
nm or less. When the film thickness is too thin, a clear multilayer film structure may not be obtained, and when it is too thick, the coercive force of the magnetic multilayer film may decrease.

Since the magnetic multilayer film of the present invention often has magnetic anisotropy in the direction perpendicular to the film surface, when it is used as a perpendicular magnetic recording medium for recording and reproduction by the perpendicular magnetic recording method,
Particularly effective. The number of laminations of the magnetic multilayer film is not particularly limited, but is preferably about 10 to 20 times. If the number of laminations is less than 10, the magnetization of the magnetic multilayer film may not be sufficient, and the signal output during recording / reproducing may be small. On the other hand, if the number of laminations exceeds 20, the thickness of the entire magnetic multilayer film may be too large, and the recording / reproducing characteristics may worsen.

In the present invention, as the non-magnetic substrate, an aluminum alloy plate or a glass substrate provided with a Ni—P layer formed by electroless plating is usually used.
In addition, any non-magnetic substrate such as a ceramic substrate, a carbon substrate, a Si substrate, and various resin substrates can be used. The substrate may be textured, but is preferably applied to a glass substrate having an Ra of 1 nm or less, which is considered to be used in many media in the future.

An underlayer for controlling crystal orientation and the like and a soft magnetic layer operating as a part of a magnetic head in perpendicular magnetic recording may be provided between the nonmagnetic substrate and the magnetic multilayer film as necessary. No problem. Normally, Ti, Ta
Etc. are preferably used. In addition, metals such as Ru and Ge or alloys thereof, or oxides such as ITO (indium tin oxide) and SiO ₂ may be used. The thickness of the underlayer is preferably 10 nm or less.

Further, a layer containing Pt or Pd as a main component may be further formed on the underlayer to a thickness of about several nm to several tens nm as a second underlayer. The layer mainly composed of Pt or Pd as the second underlayer is formed to be thicker than the layer mainly composed of Pt or Pd in the magnetic multilayer film, and is formed thereon. Has the role of improving the crystal orientation of the magnetic multilayer film.

As the soft magnetic layer, NiFe, FeSiA
1, a material having a saturation magnetic flux density (Bs) of 10 kGauss or more such as FeSi, FeTa, and CoZrNb is preferable. The thickness of the soft magnetic layer is preferably from 50 nm to 300 nm, more preferably from 100 nm to 200 n.
m or less. As the magnetic recording layer, two or more kinds of magnetic multilayer films can be combined, or another ordinary single-layer magnetic film can be combined with the magnetic multilayer film.

A protective film may be provided on the magnetic recording layer, and a lubricating layer may be further provided thereon. Examples of the protective film include a carbon film, a hydrogenated carbon film, a nitrogenated carbon film, a carbide film such as TiC and SiC, SiN, Ti by a method such as vapor deposition, sputtering, plasma CVD, ion plating, or a wet method.
Nitride films such as N, and oxide films such as SiO ₂ , Al ₂ O ₃ , and ZrO ₂ may be used. The thickness of the protective film is 5 nm or more and 30 n
m or less is preferable. Lubricants include fluorine-based lubricants,
Hydrocarbon-based lubricants and mixtures thereof can be used. The preferred film thickness is usually 1 to 4 nm.

The film forming method for forming each layer of the magnetic recording medium of the present invention is arbitrary. For example, a physical vapor deposition method such as a direct current (magnetron) sputtering method, a high frequency (magnetron) sputtering method, an ECR sputtering method, and a vacuum vapor deposition method. Is mentioned. Also, there is no particular limitation on the conditions at the time of film formation, ultimate vacuum degree, substrate heating method and substrate temperature,
The sputtering gas pressure, the bias voltage, and the like may be determined as appropriate depending on the film forming apparatus. For example, in the case of sputtering film formation, the ultimate vacuum degree is usually 5 × 10 ⁻⁴ Pa or less,
Substrate temperature is from room temperature to 400 ° C, sputtering gas is Ar, K
r, Xe or the like can be used, the sputtering gas pressure is 1 × 10 ^{−1 to} 2.5 Pa, and the bias voltage is generally 0 to −500 V. Further, trace amounts of O ₂ and N ₂ may be contained in the sputtering atmosphere.

The magnetic recording apparatus of the present invention comprises at least such a magnetic recording medium of the present invention, a drive unit for driving the magnetic recording medium in the recording direction, a magnetic head having a recording unit and a reproducing unit, and a magnetic recording medium. This is a magnetic recording apparatus having means for making relative movement with respect to a medium, and recording and reproduction signal processing means for inputting a signal to a magnetic head and reproducing an output signal from the magnetic head.

Here, when the reproducing section of the magnetic head is constituted by the MR head, a sufficient signal intensity can be obtained even at a high recording density, and a magnetic recording apparatus having a high recording density can be realized. . The recording density can be further improved by combining a signal processing circuit based on the maximum likelihood decoding method.
Even when recording / reproducing at a recording density of 0 kFCI or more and 2 Gbits per square inch or more, a sufficient S / N can be obtained.

Further, a reproducing section of the magnetic head is provided between a plurality of conductive magnetic layers which generate a large resistance change due to a relative change in their magnetization directions due to an external magnetic field, and the conductive magnetic layers. G consisting of a conductive non-magnetic layer
MR head or GM using spin valve effect
By using the R head, the signal strength can be further enhanced, and 3 gigabits or more per square inch can be achieved.
A highly reliable magnetic recording device having a linear recording density of 40 kFCI or more can be realized.

[0029]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. The substrate surface of a glass disk having an inner diameter of 25 mm and an outer diameter of 95 mm was polished to a finish of Ra (center line average roughness) of about 1 nm. The non-magnetic substrate was mounted on a single-wafer DC magnetron sputtering apparatus, evacuated to 1 × 10 ⁻⁵ Pa, and then formed into a film. The heating of the substrate and the deposition of each layer were performed after introducing the substrate into the dedicated chamber. However, the alloy layer mainly containing Co and the layer mainly containing Pt or Pd were alternately formed in the same chamber.

Example 1 A substrate was introduced into a heater chamber, the substrate was heated to 350 ° C., and an Ar gas pressure of 0.5 P
In a, a soft magnetic layer was formed to a thickness of 200 nm using a target having a composition of 45 atomic% of Ni and 55 atomic% of Fe. Subsequently, a Ta layer was formed to a thickness of 5 nm as a first underlayer at a substrate temperature of 310 ° C. and an Ar gas pressure of Pa using a Ta target.
Further, at a substrate temperature of 280 ° C. and an Ar gas pressure of 1.5 Pa, P
Using a t target, forming a Pt layer as a second underlayer by 5
nm. Using a target having a composition of 76 atomic% of Co, 15 atomic% of B, and 9 atomic% of Pt and a Pt target, a substrate temperature of 270 ° C. and an Ar gas pressure of 1.5 Pa
An oCrB alloy layer and a Pt layer were alternately laminated to form a magnetic multilayer film. The thickness of the CoCrB alloy layer is 1.2 nm, Pt
The thickness of the layer was 0.4 nm. The number of laminations is 20 (Co
20 CrB alloy layers and 20 Pt layers).
Further, a carbon protective film having a thickness of 5 nm was formed at a substrate temperature of 200 ° C. and an Ar gas pressure of 0.7 Pa using a graphite carbon target. On top of that, a fluorinated liquid lubricant (Fo)
nblin Z-Dol 2000: manufactured by Ausimont) was applied to a thickness of 1 nm to prepare a magnetic recording medium.

The magnetic characteristics of the magnetic recording medium are determined by using an MH loop tracer utilizing the Kerr effect to obtain a maximum magnetization of 20%.
The measurement was performed by applying kOe. The evaluation of recording / reproducing characteristics is G
GM using a measuring instrument Guzik1601 manufactured by Uzik
Performed with an R head. For S / N ratio, 429k
The noise component at the time of writing the FCI signal was integrated, and calculated from the reproduction output at the time of recording the 80.4 kFCI signal using the following equation. S / N = 20 log (output / noise) (Comparative Example 1) 1) All films were formed without heating the substrate. 2) 63.8 atomic% of Fe and 16.5 atomic% of Si.
A soft magnetic layer having a thickness of 200 nm was formed using a target having a composition of 19.7 atomic% of Al. 3) Using a Co target and a Pt target, a Co layer and a Pt layer were alternately formed in this order. Is 0.4 nm, the thickness of each Pt layer is 1.2 nm, the number of lamination times is 20 (Co layer and Pt layer are 20 layers each), and the Ar gas pressure is 6 Pa to produce a magnetic multilayer film. A magnetic recording medium was manufactured under the same conditions as in Example 1 and evaluated. (Comparative Example 2) 1) A soft magnetic layer having a thickness of 200 nm was formed using a target having a composition of 63.8 atomic% Fe, 16.5 atomic% Si, and 19.7 atomic% Al. 2) The substrate was heated to 160 ° C. , Co 85 atomic% Cr 15 atomic%
Using a target with a composition of
r alloy layer and Pd layer are alternately laminated in this order, and each CoC
The thickness of the r alloy layer is 0.2 nm, and the thickness of each Pd layer is 1.2
The magnetic recording medium was manufactured under the same conditions as in Example 1 except that a magnetic multilayer film was prepared by setting the number of laminations to 20 times (20 layers each for a CoCr alloy layer and a Pd layer) and setting the Ar gas pressure to 1.5 Pa. Fabricated and evaluated.

Table 1 summarizes the manufacturing conditions of the magnetic recording media of the above-mentioned examples and comparative examples. Table 2 shows the values of the coercive force in the perpendicular direction to the film surface of these magnetic recording media, the inclination of the MH loop in the perpendicular direction, and the S / N ratio. In Comparative Examples 1 and 2, the inclination A of the MH loop in the vertical direction was large, and S
/ N ratio is poor. In comparison with these, Example 1
Is that the gradient A of the MH loop in the vertical direction is 1.4 × １ ／ π
And smaller than the comparative example, and the S / N ratio also shows a good value.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

As described above in detail, according to the present invention, a magnetic recording medium having a higher coercive force and an excellent S / N ratio than a magnetic recording medium having a conventional structure, and a magnetic recording medium using this magnetic recording medium. A high-density, low-noise magnetic recording device is provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an MH curve in a direction perpendicular to a film surface of a magnetic multilayer film.

Claims (8)

[Claims] A magnetic recording layer formed on a non-magnetic substrate;
A magnetic recording medium having a magnetic multilayer film in which an alloy layer containing o as a main component and a layer containing Pt or Pd as a main component are alternately laminated, and has a magnetic characteristic perpendicular to the film surface of the magnetic multilayer film. A magnetic recording medium characterized in that the slope A at the point of M = 0 of the MH curve that satisfies the following expression. ４π (emu / cc / Oe) ≦ A <2 × １ ／ π
(Emu / cc / Oe) 2. An alloy layer containing Co as a main component is composed of Cr and B.
The magnetic recording medium according to claim 1, comprising: 3. The magnetic recording medium according to claim 1, wherein a Cr content of the alloy layer containing Co as a main component is 10 atomic% or more, and a B content is 1 atomic% or more. 4. The magnetic recording medium according to claim 1, wherein a Cr content of the alloy layer containing Co as a main component is 15 atomic% or more, and a B content is 5 atomic% or more. 5. The method according to claim 1, wherein the substrate temperature at the time of forming the magnetic multilayer film is 200.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is formed at a temperature equal to or higher than ° C. 6. 6. The magnetic recording medium according to claim 1, wherein the thickness of each of the alloy layers containing Co as a main component is 0.8 nm or more. 7. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a perpendicular magnetic recording medium. 8. A magnetic recording medium, a driving unit for driving the magnetic recording medium in a recording direction, a magnetic head including a recording unit and a reproducing unit, and means for moving the magnetic head relative to the magnetic recording medium. 8. A magnetic recording apparatus comprising: a recording signal input means for inputting a recording signal to the magnetic head and a reproduction signal output from the magnetic head; wherein the magnetic recording medium is defined by any one of claims 1 to 7. A magnetic recording device, which is a magnetic recording medium.