JP2000348335A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium high in coercive force and S/N ratio, low in PW50 value and satisfying heat fluctuation resistance. SOLUTION: A seed layer 2, an underlaid layer 3, an intermediate layer 4, a first magnetic layer 5, a nonmagnetic layer (crystal grain control layer) 6, a second magnetic layer 7, a protection layer 8 and a lubricating layer 9 are successively laminated on a glass substrate 1. The nonmagnetic layer 6 is formed from an alloy containing Cr and C and the magnetic layers are formed from the alloy containing Co and Pt.

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 magnetic tape and a magnetic disk, and more particularly to a magnetic recording medium in which the generation of noise during reproduction of a recording signal is suppressed by reducing the thickness of a magnetic layer. About.

[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. 8-227516 has been proposed. This magnetic recording medium
It has a basic structure in which two Co-Pt-based magnetic layers are provided on a substrate, and a non-magnetic layer mainly composed of Cr and Mo is interposed between the two magnetic layers. By dividing the magnetic layer into two non-magnetic layers as described above, the thickness of each magnetic layer is smaller than that of a single magnetic layer having the same total film thickness. Noise can be reduced. On the other hand, US Pat.
There has been proposed a magnetic recording medium employing a structure having a B2 structure intermetallic compound as a lower layer as described in JP-A-63-42626. The B2 structure intermetallic compound is generally called a seed layer. In particular, as a further lower layer of a Cr-based underlayer having good compatibility with the Co-based magnetic layer, fine B
By forming a seed layer having two structures, a Cr-based layer serving as an underlayer can be epitaxially grown, and a fine Cr-based underlayer can be formed. Moreover, at the same time, epitaxial growth reflecting the fine state of the underlayer can also be caused on the magnetic layer as the upper layer,
Noise can be reduced. Such a type of magnetic recording medium can be suitably used as a magnetic recording medium for an MR (magnetoresistive) head, in which suppressing noise rather than output is a priority.

[0003]

In the magnetic recording medium having the above-described structure, the magnetic layer is divided by the non-magnetic layer, so that the thickness of the magnetic layer is reduced and the crystal grain size is reduced. Therefore, noise can be suppressed. Also, noise can be suppressed by reducing the crystal grain size of the magnetic layer by epitaxial growth of the upper layer by the seed layer. However, if the crystal grain size of the magnetic layer is made very small in order to reduce noise, the magnetization becomes thermally unstable, and the recorded signal attenuates over time, eventually erasing the recorded signal. Problem. Therefore, as a fine structure of a medium that is desirable for high-density recording, the fine particles are made finer, the particle size distribution is made uniform, the dispersion of the particle size is reduced, and excessively fine particles that are easily affected by thermal fluctuations are formed. It is important to reduce production.

The present invention has been made under the above-mentioned background, and has as its object to provide a magnetic recording medium that satisfies a high coercive force, a high S / N ratio, a low PW50 value, and resistance to thermal fluctuation.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the reason why the S / N ratio, the PW50 value and the thermal fluctuation resistance cannot be sufficiently satisfied is that the crystal grain size and the grain size distribution of the magnetic layer are not sufficient. It was found that it depends on the material of the crystal grain size control layer for controlling the S / N ratio, and that only a specific alloy can achieve a high S / N ratio, a low PW50 value, and a high thermal fluctuation resistance. In particular, it has two or more magnetic layers, and at least one magnetic layer between the magnetic layers.
Finally, in the case of a magnetic recording medium having a non-magnetic layer, it was found that the magnetic layer is based on the material of the film material of the non-magnetic layer dividing the magnetic layer.
Only certain alloys have high S / N ratio, low PW50 value and
It has been found that high thermal fluctuation resistance can be achieved. The present invention has been devised under such a background, and solves the problem by adopting the following configuration.

According to the magnetic recording medium of the present invention, in a magnetic recording medium having at least a magnetic layer on a substrate, a grain size and a grain size distribution of crystal grains of the magnetic layer are controlled between the substrate and the magnetic layer. It has a crystal grain size control layer, and the crystal grain size control layer is characterized by being an alloy containing Cr (chromium) and C (carbon). In the present invention, the crystal grain size control layer is an alloy containing Cr (chromium) and C (carbon). The effect of adding C (carbon) to Cr (chromium)
Since (carbon) refines the Cr layer, it is necessary to promote the refinement of the Co particles grown on the crystal grain size control layer and to improve the particle size distribution. As a result, the number of fine particles having excessively poor heat fluctuation characteristics is reduced, the S / N ratio and the PW50 value are improved, and the heat fluctuation characteristics are also improved. The content of C (carbon) in the crystal grain size control layer is 0.1%.
It is preferably in the range of 01 at% to 0.5 at%. C
When the content of (carbon) is less than 0.01 at%, the effect of miniaturizing the crystal grain size control layer is reduced, so that the crystal size of the magnetic layer formed thereon becomes large, and the high S / N ratio is reduced. It is not preferable because the particle size distribution cannot be uniformed because heat resistance fluctuation characteristics are deteriorated. On the other hand, if the content of C (carbon) exceeds 0.5 at%, a high coercive force cannot be obtained, which is not preferable. The crystal grain size control layer has M
It is preferable to add n (manganese). In particular, when the magnetic layer is formed directly on the crystal grain size control layer, Mn contained in the crystal grain size control layer precipitates at the interface between Co and Cr in the magnetic layer, and is deposited on the Cr alloy layer. Cr in initial Co layer growing
It selectively precipitates in the phase and reduces magnetic interaction between Co grains. This further improves the S / N ratio. Therefore, by appropriately adding both of these elements, the PW
Improvement of both 50 value and S / N ratio became possible. Mn
The content of (manganese) is 0.5 at% to 5 at
% Is preferred. If the concentration is less than 0.5 at%, the effect of diffusing Mn into the Co interface of the magnetic layer cannot be expected, and the S / N
The ratio does not improve. If it exceeds 5 at%, Co of the magnetic layer
This is because the effect of diffusion of Mn into the interface is large, and the magnetic interaction between Co grains becomes extremely weak, and as a result, especially, signal attenuation is deteriorated. Furthermore, Mo (molybdenum), V (vanadium), W (tungsten), Zr (zirconium), Ti (titanium),
It may be configured to include at least one element selected from Ta (tantalum), Ni (nickel), Nb (niobium), O (oxygen), and N (nitrogen). This is for the following reason. In order to achieve a high recording density, recent magnetic disks are required to have a higher coercive force. In order to achieve a high coercive force, the Pt concentration contained in the Co-based alloy of the magnetic layer tends to increase, and at the same time, the lattice constant of the Co-based alloy increases. In order to cause epitaxial growth of the underlayer and the magnetic layer, it is necessary that the lattice constants of the underlayer and the magnetic layer match, and the crystal grain size control layer is no exception. Therefore, among the above elements, Mo,
V, W, Zr, Ti, Ta, Ni, Nb, and the like are elements having an atomic radius larger than that of Cr contained in the crystal grain size control layer, and have a function of matching the lattice constant with the magnetic layer. On the other hand, oxygen and nitrogen have a function of suppressing the growth of grains and refining crystal grains. By effectively using these two types of methods, a magnetic recording medium having a further high coercive force, a high S / N ratio, a low PW50 value, and good thermal fluctuation resistance can be obtained. The sum of the contents of these elements is
Preferably it is 2 at% to 30 at%. The reason is that if it is less than 2 at%, the lattice constant of the Cr alloy becomes smaller than that of the Co-based alloy of the magnetic layer, and if it exceeds 30 at%, it becomes too large. In each case,
This is because epitaxial growth of the magnetic layer becomes difficult, which causes a decrease in coercive force and a decrease in the S / N ratio.

[0007] The material and the like of the substrate are not particularly limited. For example, a glass substrate, a crystallized glass substrate, an aluminum alloy substrate, a ceramics substrate, a carbon substrate, a silicon substrate, or the like can be used.

The magnetic layer of the magnetic recording medium of the present invention may be a single layer or a plurality of layers. In the case of a plurality of layers, another magnetic layer may be directly laminated on the magnetic layer, or a non-magnetic layer may be interposed between the magnetic layers. The magnetic recording medium according to claims 7 to 10 of the present invention has two or more magnetic layers. The number of magnetic layers should be three or more for two or more layers in consideration of reproduction output, overwriting characteristics, and the like.
Layers, four layers, five layers, and the like. However, from a practical viewpoint, the number of layers is usually about 5 at the maximum. However, if necessary, six or more magnetic layers can be provided.

The magnetic recording medium according to claims 7 to 10 of the present invention has a non-magnetic layer in at least one of two or more magnetic layers. The non-magnetic layer is usually provided directly between the magnetic layers. However, if necessary, an intermediate layer may be provided between the nonmagnetic layer and the magnetic layer. When there are three or more magnetic layers, it is preferable to provide a non-magnetic layer between each magnetic layer. In this case, if the number of magnetic layers is n, n-1 non-magnetic layers will be provided. However, when there are three or more magnetic layers, a nonmagnetic layer may be provided between at least one of the magnetic layers without providing a nonmagnetic layer between all the magnetic layers in some cases.

It is appropriate that the thickness of each magnetic layer is 50 to 250 Å, preferably 80 to 150 Å. If the thickness of the magnetic layer is less than 50 Å, the reproduction output becomes insufficient, the coercive force decreases, and the thermal fluctuation characteristic deteriorates. This causes the PW50 value to deteriorate (decrease). It is appropriate that the thickness of each nonmagnetic layer is 5 to 100 angstroms, preferably 10 to 50 angstroms. If the nonmagnetic layer is less than 5 angstroms, the magnetic layers formed above and below the nonmagnetic layer have no magnetic separation effect, and the S / N ratio is not improved. Also, 1
If the thickness exceeds 00 angstroms, the magnetic layers formed above and below the non-magnetic layer are excessively magnetically separated, resulting in a decrease in coercive force and a deterioration in thermal fluctuation characteristics.

The film structure of the magnetic layer may be, for example, magnetic layer-nonmagnetic layer-magnetic layer-magnetic layer-nonmagnetic layer-magnetic layer in addition to the magnetic layer-nonmagnetic layer-magnetic layer shown in the following embodiments. The number of films of the magnetic layer may be further increased as a layer. Also, 2
In the above magnetic layers, the materials and thicknesses of the respective magnetic layers may be the same or different. Similarly, in the two or more nonmagnetic layers, the material and the thickness of each nonmagnetic layer may be the same or different.

In the present invention, the material of the magnetic layer is not particularly limited. As the material of the magnetic layer, for example, Co and Pt
, An alloy mainly containing Co and Ni, an alloy mainly containing Co and Cr, and the like. Specifically, CoPt, CoNi, CoCr, CoPtC
r, CoPtTa, CoPtNi, CoNiCr, Co
CrTa, CoCrPtTa, CoCrPtB, CoC
Each alloy such as rPtTaNb and CoCrPtBNb can be used. The magnetic layer of a magnetic recording medium compatible with a magnetoresistive head or a magnetic recording medium having a high coercive force is made of Co
An alloy containing Pt and Pt as main components is preferable. From the viewpoint of obtaining a sufficient coercive force, the alloy containing Co and Pt as main components is preferably an alloy having a total of 70 at% or more of Co and Pt. The ratio between Co and Pt is not particularly limited, but considering coercive force, noise, and cost, Pt (at%) / Co (at%) is in the range of 0.06 or more and 0.25 or less. Is appropriate.

There are no particular restrictions on the components other than Co and Pt. For example, Cr, Ta, Ni, Si, B, O, N,
One or more of Nb, Mn, Mo, Zn, W, Pb, Re, V, Sm, and Zr can be used as appropriate. The addition amount of these elements is appropriately determined in consideration of the magnetic characteristics and the like, and is usually preferably 30 at% or less. More specific materials for the magnetic layer include, for example, Co
PtCr alloy, CoPtTa alloy, CoPtCrTa alloy, CoPtCrNi alloy, CoPtCrB alloy and the like can be mentioned.

The magnetic layer is made of CoP from the viewpoint of noise reduction.
In the case of a tCr alloy, the preferable contents of Co, Pt, and Cr are Co: 62 to 90 at%, Pt: 5 to 20 at%,
Cr: 5 to 18 at%. In addition, CoPtCrTa
In the case of an alloy, the preferred contents of Co, Pt, Cr, and Ta are Co: 55 to 89 at%, Pt: 5 to 20 at%,
Cr: 5 to 25 at%, Ta: 1 to 7 at%, CoPt
In the case of a CrB alloy, the preferable contents of Co, Pt, Cr, and B are Co: 46 to 89 at% and Pt: 5 to 17 at.
%, Cr: 5 to 25 at%, and B: 1 to 12 at%.

Further, from the viewpoint of high coercive force, the saturation magnetic flux density Bs of the magnetic layer on the substrate side is preferably larger than the saturation magnetic flux density Bs of the magnetic layer on the medium surface side. The magnetic layer on the substrate side is considered to mainly determine the coercive force of the magnetic recording medium, and is required to have a high saturation magnetic flux density Bs. The magnetic layer on the medium surface side is considered to mainly determine the S / N ratio and corrosion resistance (corrosion resistance) of the magnetic recording medium, and is required to have a small saturation magnetic flux density Bs. In this case, the preferable range of the composition of the magnetic layer is such that when the magnetic layer is CoPtCrTa, the substrate-side magnetic layer has Co:
59 to 81 at%, Pt: 5 to 13 at%, Cr: 13
-23 at%, Ta: 1-5 at%, and in the medium surface side magnetic layer, Co: 57-79 at%, Pt: 5-13 at%.
%, Cr: 15 to 25 at%, and Ta: 1 to 5 at%.

In the present invention, the nonmagnetic layer is an alloy containing Cr and C. The effect of adding C to Cr is as follows.
In order to reduce the size of the layer, the size of the Co particles to be subsequently grown is promoted and the particle size distribution is improved. As a result, the number of fine particles having excessively poor heat fluctuation characteristics is reduced, and S / S
The N and PW are improved, and the heat fluctuation characteristics are also improved. In addition, Mn precipitates at the interface between the Co layer and the Cr layer,
It selectively precipitates in the Cr phase of the initial Co layer growing on the r alloy layer, and reduces magnetic interaction between Co grains. Thereby, the S / N is improved. Therefore, both PW and S / N can be improved by appropriately adding both of these elements.

The magnetic recording medium of the present invention may have, for example, a seed layer, an underlayer, a protective layer, a lubricating layer, etc., in addition to the magnetic layer and the nonmagnetic layer. These, seed layer,
Known underlayers, intermediate layers, protective layers and lubricating layers can be used as they are.

The seed layer is generally made of a material having a small crystal grain size and uniform crystal grains, while keeping the crystal grains of the underlayer, the intermediate layer, and the magnetic layer formed on the seed layer fine, It is provided for the purpose of improving crystal growth. As a typical material of the seed layer, a material having a B2-type crystal structure such as a NiAl alloy, a CrTi alloy,
CrNi alloy and the like can be mentioned. Note that a seed layer may be stacked to improve the crystal growth.

The underlayer is preferably made of a material that can provide a high coercive force. The underlayer can be composed of one layer or two or more layers. As the underlayer, for example,
CrMo alloy, CrV alloy, CrW alloy and the like can be used. By using a Cr alloy in this way, the lattice spacing between the magnetic layer and the underlayer 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, in-plane coercive force and electromagnetic conversion characteristics are improved. If the underlayer has the same coercive force as compared to the case where the underlayer is Cr, the thickness of the Cr alloy can be reduced, so that
An excessive increase in the particle size due to an increase in the thickness of the Cr alloy can be suppressed, and as a result, the PW and the S / N ratio are improved.

The intermediate layer is formed between the underlayer and the magnetic layer, preferably at a position in contact with the magnetic layer, and is provided for the purpose of improving the C-axis orientation of the magnetic layer. The intermediate layer is a non-magnetic material, and its crystal system is preferably matched to the crystal system of the magnetic layer. When the magnetic layer is a CoPt system as in the present invention, the HCP crystal structure having a hexagonal close-packed crystal structure Therefore, the intermediate layer has an HCP crystal structure. As the intermediate layer having the HCP crystal structure, CoCr, CoCrNb, Co
CrPt, CoCrPtTa alloy, and the like. The protective layer is provided on the magnetic layer (the surface opposite to the substrate) for the purpose of protecting the magnetic layer from destruction due to sliding contact of the head. The protective layer can be composed of one layer or two or more layers.

As the protective layer, for example, a silicon oxide film,
Examples include a carbon film, a zirconia film, a hydrogenated carbon film, a hydrogen nitrided carbon film, a carbon nitride film, a silicon nitride film, and a SiC film. Note that the protective layer can be provided by a known film formation method such as a sputtering method. The lubricating layer is provided for the purpose of reducing resistance due to sliding contact with the head, and for example, perfluoropolyether or the like is generally used. Incidentally, the crystal grain size control layer of the present invention,
It may be formed anywhere between the substrate and the magnetic layer. For example, between the substrate and the seed layer, when there are a plurality of seed layers, between the seed layer, between the seed layer and the underlayer, between the seed layer and the magnetic layer, between the substrate and the underlayer, and between the substrate and the underlayer. In the case of a plurality of layers, there are magnetic layers and the like. Specifically, the substrate /
Crystal grain size control layer / seed layer, substrate / seed layer / crystal grain size control layer / seed layer, substrate / seed layer / crystal grain size control layer /
Underlayer, substrate / seed layer / crystal grain size control layer / magnetic layer, substrate / crystal grain size control layer / underlayer / (intermediate layer) / magnetic layer, magnetic layer / crystal grain size control layer / magnetic layer, etc. The layer configuration is mentioned.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the magnetic recording medium of the present invention will be described more specifically with reference to examples. (Embodiment 1) As shown in FIG. 1, a magnetic recording medium of the present embodiment has a seed layer 2, an underlayer 3, an intermediate layer 4, a first magnetic layer 5, a non-magnetic layer 6, This is a magnetic disk in which two magnetic layers 7, a protective layer 8, and a lubricating layer 9 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 is made of a NiAl thin film (thickness: 700 Å). The NiAl thin film was made of Ni: 5
The composition ratio is 0 at% and Al: 50 at%.

The underlayer 3 is made of a CrMo thin film (film thickness: 100
Angstrom) to improve the crystal structure of the magnetic layer. In addition, this CrMo thin film is C
r: 90 at%, Mo: 10 at%. The intermediate layer 4 is made of a CoCr thin film (film thickness:
50 Å) to improve the C-axis orientation of the magnetic layer. This CoCr thin film is a nonmagnetic film having an HCP crystal structure with Co: 65 at% and Cr: 35 at%.

The first and second magnetic layers 5 and 7 are made of the same film material, CoPtCrTa alloy, and both have a thickness of 120 angstroms. The contents of Co, Pt, Cr, and Ta in these magnetic layers are as follows. That is, the first magnetic layer is made of Co: 72.5 at%,
Pt: 8 at%, Cr: 16 at%, Ta: 3.5 at
%. The second magnetic layer is composed of Co: 71 at%, Pt: 8
at%, Cr: 18 at%, and Ta: 3 at%.

The nonmagnetic layer 4 existing between the first and second magnetic layers 5 and 7 is a CrMnC thin film (thickness: 30 angstroms), and its composition ratio is Cr: 97.95.
at%, Mn: 2.00 at%, and C: 0.05 at%.

The protective layer 8 is for preventing the magnetic layer from deteriorating due to contact with the magnetic head. The protective layer 8 is formed of the first protective layer 8a and the second protective layer 8b which are sequentially stacked from the magnetic layer side. It is composed of two layers. The first protective layer 8a is
It is made of a Cr film having a thickness of 50 angstroms, and serves as a chemical protective layer for preventing the magnetic layer from deteriorating its magnetic properties due to oxidation. The other second protective layer 8b has a thickness of 1
It is made of a hydrogenated carbon film having a thickness of 00 Å and has abrasion resistance.

The lubricating layer 9 is made of a liquid lubricant of perfluoropolyether, and this film alleviates the contact with the magnetic head. The thickness is 8 Å.

Hereinafter, a method of manufacturing a magnetic disk having the above configuration will be described. First, the main surface of the glass substrate 1 chemically strengthened by ion exchange was mirror-finished (Rmax = 3.2 nm, Ra = 0.3 nm) by precision polishing. Next, on the main surface of the glass substrate 1, the seed layer 2, the underlayer 3,
An intermediate layer 4, a first magnetic layer 5, a non-magnetic layer 6, a second magnetic layer 7,
The first protective layer 8a and the second protective layer 8b were sequentially formed. (The seed layer 2, the underlayer 3, the intermediate layer 4, the first magnetic layer 5, the nonmagnetic layer 6, the second magnetic layer 7, and the first protective layer 8a are in an Ar gas atmosphere, and the second protective layer 8b is in the form of Ar + H2. (H2: 7%) was formed by sputtering in a mixed gas atmosphere.)

Next, a lubricating layer 9 was formed on the second protective layer 8b by dipping a liquid lubricant composed of perfluoropolyether to obtain a magnetic disk. As a result, the coercive force, S / N ratio, and PW50 of the obtained magnetic disk were as good as 2300 Oe, the S / N ratio was 29.5 dB, and the PW50 was 22.8 nsec. The signal attenuation is -0.080 dB / 100kfci at 60 ° C.
Dec, Ku · V / kT = 90.

The coercive force, S / N ratio, and PW50 were measured by the following measuring methods. The coercive force was measured by cutting out a sample of 8 mmφ from the manufactured magnetic disk, applying a magnetic field in the direction of the film surface, and measuring with a vibrating sample magnetometer at a maximum externally applied magnetic field of 10 kOe. Further, the recording / reproducing output was measured as follows. Using a MR head having a magnetic head flying height of 0.025 μm, recording / reproducing output was measured at a linear recording density of 346 kfcl (a linear recording density of 346000 bits per inch), with the relative speed between the MR head and the magnetic disk being 10 m / sec. . At a carrier frequency of 67.6 MHz, the measurement band is 7
The noise spectrum at the time of signal recording and reproduction was measured with a spectrum analyzer at 6.3 MHz. The MR head used for this measurement had a track width of 1.2 / 0.9 μm on the write / read side and a magnetic head gap length of 0.27 / 0.15 μm.

PW50 (half width of isolated reproduction signal)
Was measured as follows. MR for PW50 measurement
An isolated reproduction signal is extracted by an electromagnetic conversion characteristic measuring instrument (GUZIK) equipped with a head, and the width of the isolated waveform at 50% of the peak value of the output signal with respect to the ground (0) is determined by PW50.
And In addition, this PW50 has a high recording density.
The smaller, the better. 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 23.5 ns
ec or less.

Further, the measurement of the thermal fluctuation characteristic was performed as follows. First, the 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 is measured as follows. In the remanent magnetization curve measurement, the magnetic field holding time (W
Hr (t) is measured while sequentially changing the Aiming Time. 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, a minute negative magnetic field H1 is applied 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. Obtained (Hi, Mi)
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, and a negative magnetic field H1 is applied for a waiting time of 15 seconds.
After the application, the magnetic field is removed, and the residual magnetization M1 (15) is measured. Further, a positive magnetic field is applied to the sample, and a negative magnetic field H2 is set to 1
After applying for 5 seconds, the magnetic field is removed and the residual magnetization M2 (15)
Is measured. This operation is repeated until Mi (15) becomes equal to the remanent magnetization Mr. (Hi, Mi
(15)), Waiting Time
Obtain a remanence curve of 15 seconds. The H value at M = 0 is defined as Hr (15).

The same operation is performed for a holding time (Waiting
Time) 15 seconds, 30 seconds, 60 seconds, 120 seconds, 24
Repeated at 0 seconds and 480 seconds (= 8 minutes), the magnetic fields Hr (15), Hr (30), Hr (60),
Hr (120), Hr (240) Hr (480) is obtained. When this Hr (t) is plotted against the logarithm of time (Int), Hr (t) decreases linearly, and the slope dHr (t) / d (Int) causes the thermal fluctuation field Hf.
Ask for. From the Hf thus obtained, vI
sb is calculated. vIsb = kT / Hf where k is Boltzmann constant (1.38 × 100 ^{over 16} e
rg / k) and T are absolute temperatures (K) during measurement. The activation volume v is the minimum unit volume of the magnetization reversal of the magnetic layer,
VIsb obtained by multiplying this by the saturation magnetization (Isb) is the magnetic moment amount of the minimum unit of the magnetization reversal.

In the calculation of vKu / kT, v and Ku are used.
Must be measured, but Ku = (Hk · Isb) / 2
And further, the following equation is calculated assuming that Hco = Hk / 2. v · ku = v · Hk · Isb / 2 = vIsb · Hk / 2
= VIsb · Hco where Hco is the Hc due to thermal fluctuation (coercive force) before the drop occurs Hc (coercive force), which is obtained in the 10 ^{@ 9} s measurement time Hc (coercive force). Hk is the anisotropic magnetic field of the minimum unit of magnetization reversal, and vIsb is the activation magnetic moment.

Hco, which is Hc (coercive force) before the decrease in Hc (coercive force) due to thermal fluctuations, cannot be measured substantially. Therefore, Hc and vIsb are calculated using the Sherlock equation.
Hco is calculated from The Sherlock equation is an approximate equation that depends on the measurement time of Hc obtained as a result of the micromagnetics simulation and is expressed as follows. Hc / Hco = 1 − ｛(kT / vKu) ln (fo ·
t) {0.735}

When the above-mentioned assumption of Hco = Hk / 2 is taken into account, the following equation can be obtained. Hc / Hco = 1 − ｛(kT / vIsb · Hco) ln
(Fo · t) ^ 0.735} where k is Boltzmann constant (1.38 × 10 ^{over 16} er
g / k, T is the measured absolute temperature, fo 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, Hc
Since values other than o are known, Hco can be obtained by performing numerical analysis calculation of Hco. The coercive force, S / N ratio, PW50, signal attenuation, and Ku · V / kT of the following examples and comparative examples are measured based on the above-described measurement methods.

Comparative Example 1 The nonmagnetic layer 6 of CrMnC of Example 1 was formed of a CrMo thin film (Cr: 94 at%, M
o: 6 at%) (Comparative Example 1) A magnetic disk was produced in the same manner as in Example 1. When the coercive force, S / N ratio, and PW50 of these magnetic disks were measured, the coercive force was 2300 Oe, the S / N ratio was 29.5 dB, and the PW5
0 was 23.8 nsec, and a good result was not obtained for PW50. Further, the error rate also showed a higher value as compared with Example 1. The signal attenuation is 100 kfc
i, -0.095 dB / decade at 60 ° C, Ku ·
V / kT was 80. Here, in terms of the thermal fluctuation characteristics, the larger the value of the coercive force, the better. The larger the value of the S / N ratio, the smaller the noise. The smaller the PW50 (half width of isolated reproduction signal) value, the better.
It is said that if the difference is about 0 nsec, there is a difference of about 1.3 Gb / inch2. The smaller the signal attenuation, the better the thermal fluctuation resistance, which is preferable. Specifically, Ku · V / k
It is preferable that T ≧ 85.

(Examples 2-5, Comparative Examples 2-3) Example 1
The thickness of the nonmagnetic layer 6 made of CrMnC is 5 Å (Example 2), 10 Å (Example 3), 50 Å (Example 4), 100 Å (Example 5), 3 Å (Comparative Example 2). ) And 120 Å (Comparative Example 3), except that a magnetic disk was manufactured in the same manner as in Example 1. The coercive force, S / N ratio, PW50, signal attenuation (dB / decade), and Ku · V / kT of these magnetic disks are shown in FIG.
As shown in Table 1.

As is apparent from Table 1 of FIG.
It can be seen that the thickness of the nonmagnetic layer of C is preferably 5 to 100 Å in terms of coercive force, S / N ratio, magnetic properties of PW50, signal attenuation, and thermal fluctuation of Ku · V / kT.

(Examples 6 to 10, Comparative Examples 4 and 7)
1 CrMn_TwoC_0.05(Cr: 97.95 at%, M
n: 2 at%, C: 0.05 at%)
CrMn_0.5C_0.01(Cr: 99.49 at%, M
n: 0.5 at%, C: 0.01 at%) (Example)
6), CrMn _FiveC_0.01(Cr: 94.9 at%, M
n: 5 at%, C: 0.01 at%) (Example 7), C
rMn_TwoC_0.1(Cr: 97.9 at%, Mn: 2 at
%, C: 0.1 at%) (Example 8), CrMn_TwoC_0.5
(Cr: 97.5 at%, Mn: 2 at%, C: 0.5
at%) (Example 9), CrC_0.2(Cr: 99.8a
t%, C: 0.2 at%) (Example 10), CrMn_Two
(Cr: 98 at%, Mn: 2 at%) (Comparative Example 4),
CrMn_TwoC_0.55(Cr: 97.45 at%, Mn: 2
at%, C: 0.55 at%) (Comparative Example 5), CrMn
_0.4C_0.01(Cr: 99.59 at%, Mn: 0.4a
t%, C: 0.01 at%) (Comparative Example 6), CrMn₆
C_0.01(Cr: 93.99 at%, Mn: 6 at%,
C: 0.01 at%) (Comparative Example 7)
A magnetic disk was manufactured in the same manner as in Example 1. These magnetic
The disk coercive force, S / N ratio, and PW50 are shown in Table 2 in FIG.
It was as it was.

As is clear from Table 2 in FIG. 3, the nonmagnetic layer is an alloy containing at least Cr and C, and preferably is an alloy containing Cr, C and Mn and has a C content of 0%. 0.01 to 0.5 at%, Mn content is 0.5 to 5 a
It can be seen that t% is desirable.

In the above embodiment, a CrX (X: Mo, W, Ta, V, Ti) alloy may be used instead of Cr. In this case, it is CrCX. The content of X is 2 to 30 at%. In the above-described embodiment,
Although an example is described in which a nonmagnetic layer (crystal grain size control layer) made of an alloy containing Cr and C is interposed between the magnetic layers, the nonmagnetic layer (crystal grain size) of the present invention is provided below the substrate-side magnetic layer. It is also effective to provide a control layer). Hereinafter, as Examples 11 to 13,
Here are some examples.

(Embodiments 11 to 13) FIG. 4 is a diagram showing a configuration of a magnetic recording medium according to an eleventh embodiment. As shown in FIG. 4, the magnetic recording medium of Example 11 is different from the magnetic recording medium of Example 1 in that a nonmagnetic layer (crystal grain size) made of CrMnCN is further provided between the glass substrate 1 and the seed layer 2. This is an example in which a control layer 61 (film thickness: 500 angstroms) is provided. The non-magnetic layer made of CrMnCN is
A film was formed by sputtering in a mixed gas atmosphere of Ar + N2 (N2: 20 at%). Other configurations are the same as those of the first embodiment.

FIG. 5 is a diagram showing the configuration of the magnetic recording medium according to the twelfth embodiment. As shown in FIG.
The magnetic recording medium of the second embodiment is the same as the magnetic recording medium of the first embodiment except that the seed layer 2 is divided into two layers to form a first seed layer 21 and a second seed layer 22, and a CrMn layer is interposed between these seed layers.
C nonmagnetic layer (crystal grain size control layer) 62 (film thickness: 1)
5 angstrom). Other configurations are the same as those of the first embodiment.

Further, the magnetic recording medium according to the thirteenth embodiment has a material (Mn: 2a) in which 15 at% of Mo is added to the nonmagnetic layer (crystal grain size control layer) made of CrMnC of the first embodiment.
t%, C: 0.05 at%, Mo: 15 at%, Cr:
(Remaining part). Other configurations are the same as those of the first embodiment.

In the magnetic recording medium of the eleventh embodiment, the crystal orientation of the magnetic layer (Co) is improved by providing an additional CrMnC layer under the seed layer. PW50 value is equivalent, coercive force is +70
[Oe] Improved. In the magnetic recording medium of the twelfth embodiment, the seed layer (NiAl) is formed by using two seed layers.
, And the upper layer is made finer than the second seed layer by the nonmagnetic layer of CrMnC, so that the coercive force and the S / N ratio are the same as in Example 1, and the PW50 value is less than 0.1. It became smaller by 3 to 0.5 nsec and could be improved. In the magnetic recording medium of the thirteenth embodiment, the matching with the magnetic layer is improved, so that the PW50 value is equal to that of the first embodiment.
The coercive force was improved by +50 [Oe] and the S / N ratio was improved by +0.3 dB. As described above, a better result was obtained in the magnetic characteristics as compared with Example 1, and the thermal fluctuation resistance was sufficiently satisfied.

[0050]

As described in detail above, the present invention relates to a magnetic recording medium having at least a magnetic layer on a substrate,
A crystal grain size control layer for controlling the grain size and grain size distribution of crystal grains of the magnetic layer is provided between the substrate and the magnetic layer, and the crystal grain size control layer is composed of Cr (chromium) and C (carbon). ), Whereby a magnetic recording medium satisfying a high coercive force, a high S / N ratio, a low PW50 value and a thermal fluctuation resistance is obtained.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a magnetic recording medium according to a first embodiment of the present invention.

FIG. 2 is a table showing characteristics of magnetic recording media of Examples and Comparative Examples.

FIG. 3 is a table showing characteristics of magnetic recording media of Examples and Comparative Examples.

FIG. 4 is a partial sectional view of a magnetic recording medium according to Example 11 of the present invention.

FIG. 5 is a partial sectional view of a magnetic recording medium according to Example 12 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass board, 2,21,22 ... Seed layer, 3 ... Underlayer, 4 ... Intermediate layer, 5 ... First magnetic layer, 6,61,62 ... Nonmagnetic layer (crystal grain size control layer), 7 ... Second magnetic layer, 8: protective layer, 9: lubricating layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Genshichi Hatake 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Inside Hoya Corporation (72) Inventor Seiichiro Umezawa 2-chome Nakachiai, Shinjuku-ku, Tokyo No. 5 F-term in Hoya Corporation (reference) 5D006 BB07 BB08 CA01 CA05 CA06 FA09 5E049 AA04 AA09 AC05 BA06 DB04 DB12 DB20

Claims (10)

[Claims] 1. A magnetic recording medium having at least a magnetic layer on a substrate, wherein a crystal grain size control layer for controlling the grain size and grain size distribution of crystal grains of the magnetic layer is provided between the substrate and the magnetic layer. A magnetic recording medium, wherein the crystal grain size control layer is an alloy containing Cr (chromium) and C (carbon). 2. The magnetic recording medium according to claim 1, wherein said crystal grain size control layer contains 0.01 at% to 0.5 at% of C (carbon). 3. The magnetic recording medium according to claim 1, wherein the crystal grain size control layer is an alloy further containing Mn (manganese). 4. The magnetic recording medium according to claim 3, wherein the crystal grain size control layer contains 0.5 at% to 5 at% of Mn (manganese). 5. The crystal grain size control layer is made of Mo (molybdenum), V (vanadium), W (tungsten), Zr
(Zirconium), Ti (titanium), Ta (tantalum), Ni (nickel), Nb (niobium), O (oxygen), and N (nitrogen). The magnetic recording medium according to claim 1, wherein: 6. The total of the elements is 2 at% to 30 at%.
The magnetic recording medium according to claim 5, wherein 7. A magnetic recording medium having two or more magnetic layers on a substrate and having a non-magnetic layer in at least one of the magnetic layers, wherein the non-magnetic layer is any one of claims 1 to 7. A magnetic recording medium comprising the crystal grain size control layer according to any one of the preceding claims. 8. A magnetic recording medium having two or more magnetic layers on a substrate and a non-magnetic layer in at least one of the magnetic layers, wherein the non-magnetic layer is composed of Cr (chromium) and C (carbon ), And the magnetic layer is an alloy containing Co (cobalt) and Pt (platinum). 9. The magnetic recording medium according to claim 7, wherein said nonmagnetic layer has a thickness of 5 to 100 Å. 10. The magnetic layer according to claim 7, wherein the magnetic layer has a saturation magnetic flux density Bs of the substrate side magnetic layer larger than a saturation magnetic flux density Bs of the medium surface side magnetic layer. recoding media.