JP3335320B2 - Magnetic recording media - Google Patents

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 such as a hard disk mounted on an external storage device of a computer, and more particularly to a high coercive force and low noise magnetic recording medium having a seed layer provided between a substrate and a base film. It relates to a recording medium.

[0002]

2. Description of the Related Art As a magnetic recording medium of this kind, for example, a magnetic recording medium described in Japanese Patent Application Laid-Open No. 9-259418 has been proposed. This magnetic recording medium
A seed layer made of at least Al _1-x Co _x on the substrate,
A Cr or Cr alloy base film and a Co alloy magnetic layer are laminated in this order to achieve high coercive force and low noise. The higher coercive force in this magnetic recording medium is achieved by increasing the crystal orientation of the (110) plane in the body-centered cubic (bcc) of Cr or Cr alloy as the underlayer,
The crystal orientation of the (100) plane in which the axis of easy magnetization (c-axis) of the Co magnetic layer epitaxially grown thereon is parallel to the in-plane direction is improved. Further, in this magnetic recording medium, the thickness of the underlayer can be reduced by providing the seed layer. Therefore, by making the underlayer thinner, the Co magnetic particles thereon become finer, and the magnetization transition between recording bits changes. Since the area (domain wall width) can be reduced, noise can be reduced.

[0003]

However, as the thickness of the seed layer is increased in order to obtain a high coercive force, the crystal grain size and the grain size distribution forming the seed layer increase with the increase. There is a problem that the crystal grain size and the grain size distribution of the underlying film and the magnetic layer formed thereon also increase with the crystal growth and noise cannot be reduced. Also, if the crystal grain size of the magnetic layer is made very small to reduce noise, the magnetization becomes thermally unstable, and the recorded signal attenuates over time, eventually erasing the recorded signal. There is a problem that a phenomenon called thermal fluctuation occurs. Noise and thermal fluctuation are in a trade-off relationship. As the crystal grain size of the magnetic layer is reduced, noise is reduced, but signal attenuation due to thermal fluctuation increases.
The recorded signal tends to decay or disappear over time. When thermal fluctuations occur, signal attenuation (reduction of reproduction output)
In addition, the medium noise increases and the value of PW50 (half-value width of the isolated reproduction signal) deteriorates. As will be described later, the fine structure of the medium that is desirable for high-density recording is to make the crystal grains of the magnetic layer finer, reduce the particle size distribution (particle size distribution), and make the magnetic layer excessively susceptible to thermal fluctuations. It has become important to suppress the generation of fine particles.

The present invention has been made under the above-mentioned background, and has as its object to provide a magnetic recording medium which achieves high coercive force and low noise and is hardly affected by thermal fluctuation.

[0005]

The present invention has the following arrangement.

(Structure 1) In a magnetic recording medium in which at least a base layer and a magnetic layer are formed in this order on a substrate, the base layer is a seed layer for miniaturizing at least crystal grains of the magnetic layer. Wherein the seed layer has a non-magnetic film composed of at least two layers,
A magnetic recording medium characterized in that an intermediate layer made of a material different from that of the nonmagnetic film is interposed between these nonmagnetic films.

(Structure 2) The magnetic recording medium according to Structure 1, wherein a base film for adjusting the crystal orientation of the magnetic layer is formed between the seed layer and the magnetic layer.

(Structure 3) The thickness of each nonmagnetic film is 10
3. The magnetic recording medium according to Configuration 1 or 2, wherein the angle is 0 to 550 °.

(Structure 4) The thickness of the intermediate layer is 5 to 5
The magnetic recording medium according to any one of Configurations 1 to 3, wherein the angle is 0 °.

(Structure 5) The magnetic recording medium according to any one of structures 1 to 4, wherein the intermediate layer is made of a nonmagnetic material having the same crystal structure as the nonmagnetic film.

(Structure 6) The magnetic recording medium according to Structure 5, wherein the intermediate layer is made of a material that does not match the crystal lattice spacing of the nonmagnetic film.

(Structure 7) The non-magnetic film is made of NiAl, A
1Co, FeAl, FeTi, CoFe, CoTi, C
oHf, CoZr, NiTi, CuZn, AlMn, A
1Re, AgMg, CuSi, NiGa, CuBe, M
nV, NiZn, FeV, CrTi, CrNi, NiA
lRu, NiAlW, NiAlTa, MiAlHf, N
iAlMo, NiAlCr, NiAlZr, NiAlN
b. The magnetic recording medium according to Configuration 6, wherein the intermediate layer is made of a material containing one alloy selected from the group of Al ₂ FeMn ₂ , and the intermediate layer is made of a material containing Cr.

(Structure 8) The intermediate layer is composed of Cr, Mo,
The magnetic recording medium according to Configuration 7, wherein the magnetic recording medium is a material comprising at least one selected from the group consisting of V, W, and Ta.

(Constitution 9) The intermediate layer is mainly composed of Cr and W
9. The magnetic recording medium according to configuration 8, wherein the magnetic recording medium is an alloy containing:

[0015]

According to the above configuration 1, the underlayer has at least a seed layer for making crystal grains of the magnetic layer fine, and the seed layer has a nonmagnetic film composed of at least two layers. Since an intermediate layer made of a material different from that of the non-magnetic film is interposed between these non-magnetic films, the non-magnetic film becomes an initial growth film having a small crystal grain size, and a base film and / or Alternatively, since the crystal grain size of the magnetic layer becomes small, the magnetization transition region (domain wall width) can be made small and uniform, and noise is reduced. As for the coercive force, a high coercive force can be maintained by making the total thickness of the alloy films constituting the seed layer the same as that when the seed layer is formed of a single alloy film. Further, by interposing an intermediate layer between the non-magnetic films, the particle size distribution of the non-magnetic film formed on the seed layer is reduced, and when the under-film and the magnetic layer are formed, In the case where the underlayer is not formed, the particle size distribution of the magnetic layer is also reduced, so that the generation of excessively fine particles that are easily affected by thermal fluctuation can be suppressed, and therefore the influence of thermal fluctuation can be avoided. . Specifically, as shown in FIG.
The conventional magnetic recording medium (curve B) described in Japanese Patent Application Laid-Open No. 9-259418 contains excessively fine particles (portion B1) that are easily affected by thermal fluctuations. On the other hand, in the case of the present invention (curve A), excessively fine particles which are easily affected by the thermal fluctuation are reduced (B1 → A1), so that they are less affected by the thermal fluctuation. In the case of the present invention (curve A), the particle size distribution is narrow, the average particle size is small (B3 → A3), and the particles with large particle size are decreasing (B2 → A2). / N ratio and PW50 (half width of isolated reproduction signal) are improved.

The non-magnetic film constituting the seed layer is 2
Consists of more than layers. The number of non-magnetic films can be two or more, such as three, four, or five, in consideration of reproduction output, overwriting characteristics, and the like. However, from a practical point of view, usually up to 3
Layers are preferred. In the seed layer of the present invention, an intermediate layer is interposed in at least one of two or more nonmagnetic films. This intermediate layer has a function of temporarily blocking the crystal growth of the nonmagnetic film. When there are three or more nonmagnetic films, it is preferable to provide an intermediate layer between each nonmagnetic film. In this case, if the number of nonmagnetic films is n, n-1 intermediate layers are provided. However, when there are three or more nonmagnetic films, an intermediate layer may be provided between at least one of the nonmagnetic films without providing an intermediate layer between all the nonmagnetic films in some cases. As the film configuration of the seed layer, in addition to the non-magnetic film-intermediate layer-non-magnetic film shown in the examples described later,
For example, a non-magnetic film-intermediate layer-non-magnetic film-intermediate layer-non-magnetic film, or a non-magnetic film-intermediate layer-non-magnetic film-non-magnetic film-intermediate layer-non-magnetic film The number may be further increased. The material and the thickness of each non-magnetic film in the two or more non-magnetic films may be the same or different. Similarly, in the two or more intermediate layers, the material and the thickness of each intermediate layer may be the same or different. Further, the intermediate layer of the non-magnetic film blocks crystal growth of the non-magnetic film below the intermediate layer,
The role of the non-magnetic film (underlayer, magnetic layer) formed on the intermediate layer in which generation of excessively fine particles is suppressed, the average crystal grain size is small, and the grain size distribution is small (narrow). There is.

In the present invention, as in the above configuration 2, an underlayer may be formed between the seed layer and the magnetic layer for the purpose of adjusting the crystal orientation of the magnetic layer. Here, it is preferable that the base film is made of a material that can obtain a high coercive force. The base film can be composed of one layer or two or more layers. As the base film, for example, CrMo alloy, CrV alloy, C
An rW alloy or the like can be used. By using a Cr alloy as described above, when the magnetic layer is a Co alloy, the lattice spacing between the magnetic layer and the underlying film is well matched, so that the easy axis of magnetization of the magnetic layer is easily oriented in the in-plane direction. As a result, coercive force and electromagnetic conversion characteristics are improved. In addition, the underlayer is made of Cr.
If the coercive force is the same as in the case of the above, the thickness of the Cr alloy can be reduced, so that an excessive increase in the particle size due to the increase in the thickness of the Cr alloy can be suppressed. Is improved.

In the present invention, if necessary, an intermediate film may be formed between the underlayer and the magnetic layer, preferably at a position in contact with the magnetic layer. This intermediate film is provided for the purpose of improving the C-axis orientation of the magnetic layer. This intermediate film is a non-magnetic material, and its crystal system is desirably adjusted to the crystal system of the magnetic layer. For example, when the magnetic layer is a CoPt system, it has an HCP crystal structure having a hexagonal close-packed crystal structure. Therefore, the intermediate film has an HCP crystal structure, CoCr, Co
CrNb, CoCrPt, CoCrPtTa alloy and the like are preferable.

According to the present invention, as in the above configuration 3, in view of miniaturization and uniformity of the crystal grain size of the nonmagnetic film and coercive force, the thickness of each nonmagnetic film constituting the seed layer is: 150 ~
It is desirable that the thickness be 550 ° and the total film thickness is 300 to 1100 °. If the thickness of each non-magnetic film is less than 100 °, the coercive force is greatly reduced, which is not preferable.
When the ratio is more than the above, the crystal grain size and the grain size distribution of the non-magnetic film become large, and the crystal grain size of the underlayer and / or the magnetic layer becomes large with the increase. The total thickness of the non-magnetic film constituting the seed layer is:
It can be appropriately adjusted depending on the coercive force to be obtained.

In the present invention, the thickness of the intermediate layer is preferably 5 to 50 ° from the viewpoint of noise reduction as in the above configuration 4. That is, if the thickness of the intermediate layer is less than 5 °, the role of blocking the crystal growth of the non-magnetic film constituting the seed layer is not fulfilled, and the upper non-magnetic film reflects the crystal growth of the lower non-magnetic film as it is. Since the magnetic film is formed, the crystal grain size and the grain size distribution are increased, the noise is increased, and the influence of thermal fluctuation is likely to occur. On the other hand, if it exceeds 50 °, the crystal grain size of the intermediate layer becomes large, so that the crystal grain size and the particle size distribution of the upper non-magnetic film become large, and noise becomes large.

In the present invention, it is preferable that the intermediate layer is made of a non-magnetic material having the same crystal structure as that of the non-magnetic film in order to improve the crystal growth of the magnetic layer.

In the present invention, as in the above configuration 6, the intermediate layer may be made of a material that does not match the crystal lattice spacing of the non-magnetic film. Is preferred. Specifically, the difference between the crystal lattice plane spacings of the intermediate layer and the nonmagnetic film is preferably about 0.001 to 0.011 nm.

In the present invention, as in the above configuration 7, the non-magnetic film only needs to generally fulfill the role of a seed layer (to make the crystal grain size of the magnetic layer uniform and finer).
For example, NiAl, AlCo, FeAl, FeTi, C
oFe, CoTi, CoHf, CoZr, NiTi, C
uZn, AlMn, AlRe, AgMg, CuSi, N
iGa, CuBe, MnV, NiZn, FeV, CrT
i, CrNi, NiAlRu, NiAlW, NiAlT
a, MiAlHf, NiAlMo, NiAlCr, Ni
One alloy selected from the group of AlZr, NiAlNb, and Al ₂ FeMn ₂ is preferable, and the intermediate layer is preferably made of a material containing Cr. Among them, NiAl, CrTi, and NiAlRu, which have a uniform crystal grain size and a high effect of reducing noise due to miniaturization, are preferable.

In the present invention, as in Configuration 8, the intermediate layer is preferably a Cr alloy composed of Cr and at least one selected from the group consisting of Mo, V, W and Ta.
This is preferable in the case of the above-described Cr alloy because only the growth and distribution of the grain size can be suppressed without impairing the matching between the upper and lower seed layers, and the magnetic characteristics are less varied. Mo, V,
The content of at least one selected from W and Ta is 5 to 5.
30 at% is preferable.

In the present invention, as in the ninth aspect, it is particularly preferable that the intermediate layer is an alloy mainly containing Cr and W. This is because when a CrW alloy is used as the intermediate layer, variations in magnetic characteristics are small and productivity is stable. When this CrW alloy is used, the content of W is preferably 5 to 30 at%. If less than 5at%,
The effect of suppressing the grain growth of the seed layer and making the grain size distribution uniform is lost. If it exceeds 30 at%, matching with the upper seed layer becomes poor, and PW characteristics, S / N ratio,
It is not preferable because the coercive force is deteriorated. In addition, for example,
Other elements such as Nb may be contained at about 2 at% or less.

In the above-described magnetic recording medium of the present invention, the material of the substrate is not particularly limited. For example, a glass substrate, a crystallized glass substrate, an aluminum alloy substrate,
A ceramic substrate, a carbon substrate, a silicon substrate, or the like can be used.

In the magnetic recording medium of the present invention, the magnetic layer is not particularly limited. As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiC containing Co as a main component is used.
r, CoCrTa, CoPtCr, CoNiPt or Co
NiCrPt, CoNiCrTa, CoCrPtTa,
A magnetic film of CoCrPtB, CoCrPtTaNb, or the like may be used. The magnetic layer has a multilayer structure (for example, CoCr) in which the magnetic film is divided by a non-magnetic film (for example, Cr, CrMo, CrV, CrMnC, etc.) to reduce noise.
PtTa / CrMo / CoCrPtTa). As a magnetic layer corresponding to a magnetoresistive head (MR head) or a giant (large) magnetoresistive head (GMR head), Co, Y, Si, rare earth elements, Hf,
An impurity element selected from Ge, Sn, and Zn, or an element containing an oxide of these impurity elements is also included. Examples of the magnetic layer include, in addition to the above, a ferrite type, an iron-rare earth type, and a granular having a structure in which magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of SiO ₂ or BN. It may be. The magnetic layer may have any of an in-plane type and a vertical type.

On the magnetic layer, a protective layer and a lubricating layer can be formed as required. The protective layer is formed for the purpose of protecting the magnetic layer from destruction due to sliding contact of the magnetic head. The protective layer can be composed of one layer or two or more layers. As the protective layer, for example, a chromium film, a silicon oxide film, a carbon film, a hydrogenated carbon film, a carbon nitride film,
Examples thereof include a hydrogen nitrided carbon film, a zirconia film, a silicon nitride film, and a silicon carbide film. Note that the protective layer can be formed by a known film formation method such as a sputtering method. The lubricating layer is provided for the purpose of reducing the resistance due to sliding contact with the magnetic head. For example, a liquid lubricant such as perfluoropolyether is generally used.

[0029]

EXAMPLES The magnetic recording medium of the present invention will be further described below with reference to examples. Embodiment 1 As shown in FIG. 2, the magnetic recording medium of this embodiment has a seed layer 2, a base film 3, an intermediate layer 4, a magnetic layer 5,
This is a magnetic disk in which a protective layer 6 and a lubricating layer 7 are sequentially laminated. The glass substrate 1 is made of chemically strengthened aluminosilicate glass, and has a surface roughness Rmax =
Mirror-polished to 3.2 nm, Ra = 0.3 nm. The seed layer 2 includes two alloy films 21 and 23
And an intermediate layer 22 interposed between these alloy films to block the crystal growth of the alloy film 21.
1 is a NiAl thin film (thickness 300 °), and the intermediate layer 22 is
The CrW thin film (thickness 30 °) and the alloy film 23 are NiAl thin films (thickness 300 °). The alloy films 21 and 23
Is composed of Ni: 50 at%, Al:
The CrW thin film having a composition ratio of 50 at% and constituting the intermediate layer 22 has a composition ratio of Cr: 90 at% and W: 10 at%. The underlayer film is a CrMo thin film (thickness: 100 °) and is provided to improve the crystal structure of the magnetic layer. This CrMo thin film has a Cr: 9
The composition ratio is 0 at% and Mo is 10 at%. The intermediate layer 4 is made of a CoCr thin film (thickness: 30).
Å) In order to improve the C-axis orientation of the magnetic layer. This CoCr thin film is made of Co: 65 at.
%, Cr: 35 at% is a nonmagnetic film having an HCP crystal structure. The magnetic layer 5 is a CoCrPtTa alloy thin film (film thickness: 240 °). The contents of Co, Cr, Pt, and Ta are as follows: Co: 72.5 at%, Cr: 16 at%, P:
t: 8 at% and Ta: 3.5 at%. The protective layer 6 is for preventing the magnetic layer from being deteriorated due to contact with the magnetic head, and is made of a hydrogenated carbon film having a thickness of 100 °. The lubricating layer 7 is made of a liquid lubricant of perfluoropolyether, and this film alleviates the contact with the magnetic head. The thickness is 8 °.

Next, a method of manufacturing the magnetic disk having the above-described configuration will be described. First, the main surface of the glass substrate 1 chemically strengthened by ion exchange is mirror-finished (Rmax = 3.2 nm, Ra = 0.3 nm) by precision polishing. Next, on the main surface of the glass substrate 1, a seed layer 2, a base film 3,
An intermediate layer 4, a magnetic layer 5, and a protective layer 6 were sequentially formed. Next, a lubricating layer 7 was formed on the protective layer 6 by dipping a liquid lubricant composed of perfluoropolyether to obtain a magnetic disk.

The coercive force of the obtained magnetic disk, S /
As a result of measuring the N ratio and the PW50 (half width of the isolated reproduction signal), the coercive force was good at 2800 Oe, the S / N ratio was 29.43 dB, and the PW50 was also good at 18.78 nsec. The output signal attenuation is 100Kfci, 6
-0.05dB / decade at 0 ° C, K showing thermal fluctuation characteristics
u · v / kT was also good at 110. Here, in terms of thermal fluctuation resistance, the larger the value of the holding force, the better. The larger the value of the S / N ratio is, the smaller the noise is.
If the difference is about 0.5 dB, the recording density is about 0.6 Gb / inc.
the difference between the h ² it is said that there is. It is said that the smaller the PW50 (half value width of the isolated reproduction signal) value is, the smaller it is. If the difference is about 0.6 nsec, it is said that there is a difference of about 0.8 Gb / inch ^{2 in} the recording density. The smaller the output signal attenuation, the better.
The larger the value of Ku · v / kT, the better the resistance to thermal fluctuations is, so it is preferable. Specifically, the value of Ku · v / kT is 90
Above is good.

The coercive force, S / N ratio, PW50,
Output signal attenuation characteristics and thermal fluctuation characteristics (Ku · v / kT) were measured by the following measurement methods.

The coercive force was measured by cutting a sample of 8 mmφ from the manufactured magnetic disk, applying a magnetic field in the direction of the film surface, and applying a maximum externally applied magnetic field of 10 kO by a vibrating sample magnetometer.
e.

The S / N ratio was determined by measuring the recording / reproducing output as follows. Magnetic head flying height is 0.025
The relative speed between the MR head and the magnetic disk is set to 10 m using a μm magnetoresistive head (hereinafter referred to as MR head).
The recording / reproducing output at a linear recording density of 346 kfcl (a linear recording density of 346,000 bits per inch) was measured as / sec. Also, the carrier frequency is 67.6 MH.
At z, the measurement bandwidth was 76.3 MHz, and the noise spectrum during signal recording and reproduction was measured by a spectrum analyzer. The MR head used for this measurement was written /
The track width is 1.2 / 0.9 μm on the reading side,
The magnetic head gap length is 0.27 / 0.15 μm.

The measurement of PW50 (half width of isolated reproduction signal) was performed as follows. An isolated reproduction signal was extracted by an electromagnetic conversion characteristic measuring instrument (GUZIK) equipped with an MR head for measuring PW50, and the width of the isolated waveform at 50% of the peak value of the output signal with respect to the ground (0) was defined as PW50. The smaller the PW50 is, the better the recording density is. This is because if the pulse width is small, more pulses (signals) can be written on the same area. On the other hand, if the PW50 is large, adjacent pulses (signals) interfere with each other and appear as an error when reading out the signal. This waveform interference degrades the error rate. From these, PW50 is 19.2 nsec.
It must be:

The measurement of the output signal attenuation characteristic was performed as follows. Only the signal attenuation due to the thermal fluctuation of the magnetic recording medium is not affected by the thermal off-track (a phenomenon in which the magnetic head is shifted with respect to the track on the magnetic recording medium due to the thermal expansion of the head suspension, causing signal attenuation). For accurate evaluation, an MR head characterized in that it has a read / write element whose write track width is twice or more as large as the read track width is prepared. Set it in the head / disk mechanism. Next, the head / disk mechanism is placed in a temperature-controllable environmental bath in order to expose it to a high-temperature environment. When the temperature in the environmental chamber stabilizes to the set temperature, the read signal is sent from the read / write circuit to the MR.
The signal is sent to the write element of the head and a signal is written to the magnetic disk. Immediately after writing the signal, the signal written on the magnetic disk is read from the read element of the MR head, amplified by the read / write circuit section, and measured by the signal evaluation section. The signal evaluation unit records the amplitude value of the read signal at regular time intervals. The signal evaluation unit performs measurement using, for example, a spectrum analyzer. The conditions for this measurement were as follows: the temperature of the environmental bath was 60 ° C., and the recording density of the signal written on the magnetic disk was 100 KFlux / inc
h. The head used in this measurement had a write track width of 12.0 μm and a read track width of 2.4 μm.
m, the write gap length is 0.35 μm, the read gap length is 0.30 μm, and the flying height of the read / write element portion is 2
0 nm MR head.

The measurement of the thermal fluctuation characteristics was performed as follows. Activation magnetic moment (vIsb), which is the product of the activation volume (v) and the saturation magnetization (Isb) of the minimum unit of magnetization reversal
Was calculated by Hf (thermal fluctuation field) obtained by the Waiting Time method. The Waiting Time method measures as follows. Waiting time of magnetic field in remanent magnetization curve measurement
Are sequentially changed, and Hr (t) is measured. A sample cut to φ8 mm is set on a VSM (sample signal magnetometer), and a sufficiently large positive magnetic field is applied to the sample. Next, the slight negative magnetic field H
Apply 1 to remove the magnetic field. The remaining magnetization M1 is measured.
Next, a positive magnetic field is applied again, a magnetic field H2 larger than H1 is applied, and the residual magnetization M2 after removing the magnetic field is measured. The same operation is repeated until Mi becomes the remanent magnetization Mr.
The obtained (Hi, Mi) is plotted to obtain a remanent magnetization curve. The magnetic field H value at M = 0 is defined as Hr (remanence coercive force). Next, a sufficiently large positive magnetic field is applied to the sample, a negative magnetic field H1 is applied for a waiting time of 15 seconds, the magnetic field is removed, and the residual magnetization M1 (15) is measured. Further, after applying a positive magnetic field to the sample and applying a negative magnetic field H2 for 15 seconds, the magnetic field is removed and the residual magnetization M2 (15) is measured. This operation is repeated until it becomes equal to Mi (15) residual magnetization Mr.
The obtained (Hi, Mi) (15) is plotted, and the Waiting Time
Obtain a remanence curve of 15 seconds. The H value at M = 0 is H
It is defined as r (15). Hold the same operation for the holding time (Waiting Ti
me) 15 seconds, 30 seconds, 60 seconds, 120 seconds, 240 seconds, 4
Repetition was performed for 80 seconds (= 8 minutes), and the magnetic fields Hr (15), Hr (30), Hr (60), Hr (120), Hr (24
0), Hr (480) is obtained. This Hr (t) is expressed as the logarithm of time (ln
When plotted with respect to t), Hr (t) decreases linearly, and the thermal fluctuation field Hf is obtained from the slope dHr (t) / d (lnt). From the Hf thus obtained, vIsb is calculated by the following equation. vIsb = kT / Hf where k is Boltzmann's constant (1.38 × 10 ⁻¹⁶ er)
g / K) and T is the absolute temperature (K) during the measurement. The activation volume v is a volume of the minimum unit of the magnetization reversal of the magnetic layer, and vIsb obtained by multiplying this by the saturation magnetization (Isb) is the magnetic moment amount of the minimum unit of the magnetization reversal. In addition, for the calculation of v · Ku / kT, it is necessary to measure v and Ku.
(Hk · Isb) / 2, and Hc0 == Hk
/ 2 and is calculated by the following equation. v · Ku = V · Hk · Isb / 2 = vIsb · Hk / 2 = vIs
b · Hc0 Here, Hc0 is Hc (coercive force) before Hc (coercive force) decreases due to thermal fluctuation, and is Hc (coercive force) obtained in a measurement time of 10 ⁻⁹ sec. Hk is an anisotropic magnetic field of the minimum unit of magnetization reversal, and vbIsb is an activation magnetic moment. Since Hc0, which is the Hc (coercive force) before Hc (coercive force) decrease due to thermal fluctuation, cannot be substantially measured, Hc and vIs are calculated using the Sherlock equation.
Hc0 is calculated from b. The Sherlock equation is an approximate equation that depends on the measurement time of Hc obtained as a result of the micro-magnetics simulation and is expressed as follows. Hc / Hc0 = 1 − ｛(kT / v · Ku) ln (f0 ·
t) {0.735} When the above-mentioned assumption of Hc0 = Hk / 2 is put, the following equation is obtained. Hc / Hc0 = 1 − ｛(kT / vIsb · Hc0) ln (f0
T) {0.735} where k is Boltzmann's constant (1.38 × 10 ⁻¹⁶ erg)
/ K), T is the measured absolute temperature, f0 is the vibration factor (10 ＾ 9)
Hz), t is the measurement time (600 sec), and vIsb is the activation magnetic moment (emu). In the above equation, Hc0
Since Hc0 is known, Hc0 can be obtained by numerical analysis of Hc0. Incidentally, the coercive force, S / N ratio, P
W50, output signal attenuation characteristics, and thermal fluctuation characteristics were measured based on the above-described measurement methods.

[0038] NiA the seed layer 2 of Comparative Example 1 Example 1, a single layer having a thickness of 600Å
A magnetic disk was manufactured in the same manner as in Example 1, except that the thin film (Ni: 50 at%, Al: 50 at%) was used. The coercive force, S / N ratio, PW50,
When the output signal attenuation characteristics and Ku · v / kT were measured,
The coercive force is 2800 Oe, the S / N ratio is 29.63 dB,
PW50 was 19.4 nsec, and good results could not be obtained for the value of PW50. Here, in order to generally increase the coercive force, an underlayer having a certain thickness is required. However, as the thickness of the underlayer increases, the crystal grain size of the magnetic layer increases, and the PW50 and the S / N ratio deteriorate. When the seed layer 2 of the first embodiment is used, PW50,
A desired coercive force can be obtained while maintaining the S / N ratio. Further, the magnetic disk of Comparative Example 1 also exhibited a higher error rate than that of Example 1. further,
The output signal attenuation is -0.07 dB / decade under the measurement conditions of 100 Kfci and 60 ° C., and Ku · v showing the thermal fluctuation characteristic.
The value of / kT was also 100, and the thermal fluctuation resistance was lower than that of Example 1.

Example 2 and Comparative Example 2 The thickness of the magnetic layer 5 in Example 1 and Comparative Example 1 was 18
A magnetic disk was manufactured in the same manner as in Example 1 and Comparative Example 1 except that the temperature was set to 0 ° or less. The coercive force, S / N ratio, PW50, output signal attenuation characteristics, Ku ·
When v / kT was measured, it was as follows.

[0040]

[Table 1]

As shown in Table 1, as the thickness of the magnetic layer becomes thinner, the influence of the thermal fluctuation becomes remarkable. The case where the divided seed layer 2 of the first embodiment is used (Example 2) and the case of the comparative example 1 are different. The difference in the output signal attenuation (-dB / decade) is larger in the case where the single-layer seed layer is used (Comparative Example 2). As shown in FIG. 3, when the thickness t (Mr is residual magnetization) of the magnetic layer is large (M
(rt = around 0.5 to 0.6) (in the case of Example 1 and Comparative Example 1) is the output signal attenuation (-dB / deca) due to the difference in the seed layer.
Although the difference in de) is small, as the thickness of the magnetic layer becomes thinner (Mrt = approximately 0.4 to 0.3), when the divided seed layer is used (curve A) and when the single-layer seed layer is used. In the case (curve B), the difference in output signal attenuation (-dB / decade) becomes large, and the effect of thermal fluctuation becomes remarkable. In general, miniaturization of magnetic particles decreases the value of Ku · v / kT. In the present invention, however, the number of excessively fine particles that are narrow in particle size distribution of magnetic particles and easily affected by thermal fluctuations is reduced. Since it is small, the value of Ku · v / kT does not decrease even if the magnetic particles are miniaturized, and the thermal fluctuation resistance is good.

Example 3 The magnetic layer 5 of Example 1 was replaced by a first magnetic layer 51, a divided layer 52,
The second magnetic layer 53 is formed, and the protective layer 6 is formed of the first protective layer 61 and the second protective layer 61.
A magnetic disk was manufactured in the same manner as in Example 1 except that the protective layer 62 was used. The first magnetic layer 51 and the second magnetic layer 53 are made of the same film material, CoCrPtT.
It is made of alloy a and has a thickness of 120 °. The contents of Co, Cr, Pt, and Ta in these magnetic layers are the first.
The magnetic layer is composed of Co: 72.5 at%, Cr: 16 at%,
Pt: 8 at%, Ta: 3.5 at%, the second magnetic layer is composed of 71 at% of Co, 18 at% of Cr, and 8 a of Pt.
t%, Ta: 3 at%. The split layer 52 interposed between the first magnetic layer 51 and the second magnetic layer 53 is a CrMnC thin film (thickness: 30 °) made of a non-magnetic material.
The composition ratio is as follows: Cr: 97.95 at%, Mn: 2.0
0 at% and C: 0.05 at%. The first protective layer 61 is made of a Cr film having a thickness of 50 ° and plays a role of a chemical protective film for preventing the magnetic layer from deteriorating magnetic characteristics due to oxidation. The second protective layer has a thickness of 100 °
Is a hydrogenated carbon film.

The coercive force, S / N ratio, P
When W50, output signal attenuation characteristics and Ku · v / kT were measured, the coercive force was 2580 Oe and the S / N ratio was 30.7.
The dB and PW50 were 19.1 nsec, and good results were obtained. The output signal attenuation is 100Kfci, 60
-0.08dB / decade at ℃, Ku showing thermal fluctuation characteristics
・ V / kT was also good at 90. In the third embodiment, since the magnetic layer is divided and the particle diameter of the magnetic particles is reduced, the magnetic layer is more susceptible to the thermal fluctuation than the magnetic recording medium of the first embodiment.

Comparative Example 3 The seed layer of Example 3 was replaced with a single layer of NiAl having a thickness of 600 °.
A magnetic disk was manufactured in the same manner as in Example 3 except that the thin film (Ni: 50 at%, Al: 50 at%) was used. The coercive force, S / N ratio, PW50,
When the output signal attenuation characteristics and Ku · v / kT were measured,
Coercivity is 2580 Oe, S / N ratio is 30.6dB, P
W50 is 19.6 nsec, output signal attenuation is -0.10
The dB / decade and Ku · v / kT were 80.

Examples 4 to 7 and Comparative Examples 4 and 5 The alloy films 21 and 23 constituting the seed layer 2 of Example 1 have a thickness of 90 ° (Comparative Example 4), 100 ° (Example 4) and 250 ° (comparative example). Example 5), 450 ° (Example 6),
A magnetic disk was manufactured in the same manner as in Example 1 except that the temperature was changed to 550 ° (Example 7) and 600 ° (Comparative Example 5). The coercive force, S / N ratio, PW5 of these magnetic disks
0, the output signal attenuation characteristics, and Ku · v / kT were as follows.

[0046]

[Table 2]

As shown in Table 2, the thickness of the alloy films 21 and 23 constituting the seed layer 2 should be in the range of 100 to 550 °, depending on the coercive force, the S / N ratio (noise), and the magnetic property of the PW50. It can be seen that this is preferable in terms of characteristics, output signal attenuation characteristics, and thermal fluctuation characteristics (Kuv / kT).

Examples 8 to 10 and Comparative Examples 6 and 7 The intermediate layer 22 in Example 1 was made of CrMo (Mo: 10a).
t%), and the thickness of the intermediate layer 22 is 4Å
(Comparative Example 6) A magnetic disk was manufactured in the same manner as in Example 1 except that the angles were changed to 5 ° (Example 8), 15 ° (Example 9), 50 ° (Example 10), and 60 ° (Comparative Example 7). did. The coercive force, S / N ratio, P
W50, output signal attenuation characteristics, and Ku · v / kT were as follows.

[0049]

[Table 3]

As shown in Table 3, the thickness of the intermediate layer 22 is
The coercive force, S / N ratio, P
W50, output signal attenuation characteristics, and thermal fluctuation characteristics (K
u · v / kT).

The intermediate layer 22 (Cr
W (W: 10 at%)), an experiment was conducted in the same manner, but the coercive force, S / N ratio, P
W50 was a good value. The difference from the CrMo alloy is that when the film thickness is in the range of 5 to 50 °, the coercive force: 28
20 Oe, noise: 29.3 dB, PW50: 18.
That is, each value of 6 nsec was constant. this is,
CrW alloy, compared to other Cr alloys such as CrMo alloy,
It is considered that the material is unlikely to change its crystal growth property with respect to a change in the film thickness with the seed layer. That is, the variation in each magnetic characteristic is small and the productivity is stable.

Embodiments 11 to 16 The film material of the alloy films 21 and 23 constituting the seed layer 2 of the embodiment is NiAlRu (Ni: 45 at%, Al: 50a).
t%, Ru: 5 at%) (Example 11), CrTi (C
r: 80 at%, Ti: 20 at%) (Example 12),
CrNi (Cr: 60 at%, Ni: 40 at%) (Example 13), FeAl (Fe: 50 at%, Al: 50)
at%) (Example 14), NiAlW (Ni: 50 at)
%, Al: 45 at%, W: 5 at%) (Example 1)
5), NiAlNb (Ni: 50 at%, Al: 45a)
t%, Nd: 5 at%) (Example 16) A magnetic disk was manufactured in the same manner as in Example 1 except that the magnetic disk was changed to N%. The coercive force, S / N ratio, PW50, output signal attenuation characteristics, and Ku · v / kT of these magnetic disks were as follows.

[0053]

[Table 4]

As shown in Table 4, when the film materials of the alloy films 21 and 23 are NiAlRu, CrTi and CrNi, the coercive force, the noise, the magnetic characteristics of the PW50, the output signal attenuation characteristics, and the thermal fluctuation characteristics From the point of (Ku.v / kT), it is understood that it is particularly preferable among the materials shown in Table 4.

Examples 17 to 19 The film material of the intermediate layer 22 in Example 1 was changed to CrMo.
(Cr: 90 at%, Mo: 10 at%) (Example 1)
7), CrV (Cr: 80 at%, V: 20 at%)
(Example 18), CrTa (Cr: 95 at%, Ta:
5 at%) (Example 19), except that 100 magnetic disks were manufactured in the same manner as in Example 1. The coercive force, S / N ratio, PW5 of these magnetic disks
0, the output signal attenuation characteristics, and Ku · v / kT were as follows.

[0056]

[Table 5]

As shown in Table 5, when the film material of the intermediate layer 22 is CrW, it is preferable because the magnetic characteristics have little variation and the productivity is stable. This is CrW
This is because the lattice matching with the seed layer is better than that of a Cr alloy film such as CrMo, and therefore, the change in characteristics due to the change in the thickness of CrW is small.

[0058]

As described above, according to the present invention, it is possible to obtain a magnetic recording medium which achieves high coercive force and low noise and is hardly affected by thermal fluctuation.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the function of a seed layer of the present invention.

FIG. 2 is a diagram schematically showing a magnetic disk according to one embodiment of the present invention.

FIG. 3 is a diagram for explaining the relationship between the thickness of a magnetic layer and the effect of thermal fluctuation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 1 2 Seed layer 3 Underlayer 4 Intermediate layer 5 Magnetic layer 6 Protective layer 7 Lubrication layer 21 Non-magnetic film 22 Intermediate layer 23 Non-magnetic film

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Satoshi Yokota Republic of Singapore 638552 Link 2 Tour # 3 Hoya Magnetics Singapore Private Limited (72) Inventor Seiichiro Umezawa 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo No. Masaaki Kurano, Inspector in Hoya Co., Ltd. (56) References JP-A-9-259418 (JP, A) JP-A-9-16941 (JP, A) JP-A-10-134334 (JP, A) JP-A-8-22616 (JP, A) JP-A-1-199314 (JP, A) JP-A-8-249640 (JP, A) JP-A-11-73621 (JP, A) JP-A-10-214412 ( JP, A) JP-A-9-212843 (JP, A) WO 98/6093 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/73 G11B 5/66

Claims (9)

(57) [Claims] 1. A magnetic recording medium in which at least a base layer and a magnetic layer are formed in this order on a substrate, wherein the base layer has at least a seed layer for making crystal grains of the magnetic layer fine. Wherein the seed layer has a non-magnetic film composed of at least two or more layers, and an intermediate layer made of a material different from the non-magnetic film is interposed between these non-magnetic films. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein a base film for adjusting the crystal orientation of the magnetic layer is formed between the seed layer and the magnetic layer. 3. The method according to claim 1, wherein each of the nonmagnetic films has a thickness of 100 to 55.
The magnetic recording medium according to claim 1, wherein the angle is 0 °. 4. The magnetic recording medium according to claim 1, wherein said intermediate layer has a thickness of 5 to 50 °. 5. The magnetic recording medium according to claim 1, wherein the intermediate layer is made of a non-magnetic material having the same crystal structure as the non-magnetic film. 6. The magnetic recording medium according to claim 5, wherein the intermediate layer is made of a material that does not match a crystal lattice spacing of the nonmagnetic film. 7. The non-magnetic film according to claim 1, wherein the non-magnetic film is made of NiAl, AlCo,
FeAl, FeTi, CoFe, CoTi, CoHf,
CoZr, NiTi, CuZn, AlMn, AlRe,
AgMg, CuSi, NiGa, CuBe, MnV, N
iZn, FeV, CrTi, CrNi, NiAlRu,
NiAlW, NiAlTa, MiAlHf, NiAlM
o, NiAlCr, NiAlZr, NiAlNb, Al
Made of a material containing one alloy selected from the group consisting of ₂ FeMn _2, wherein the intermediate layer is a magnetic recording medium according to claim 6, characterized in that a material containing Cr. 8. The intermediate layer comprises Cr, Mo, V, W, T
8. The magnetic recording medium according to claim 7, wherein the material comprises at least one member selected from the group consisting of: a. 9. The magnetic recording medium according to claim 8, wherein the intermediate layer is mainly composed of an alloy containing Cr and W.