JP2001195721A - Magnetic storage device with magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic storage device capable of high density information recording and reproduction and having high reliability. SOLUTION: The magnetic storage device has a magnetic recording medium, a magnetic head comprising a driving part which drives the medium in the recording direction, a recording part and a reproducing part, a means of moving the magnetic head relatively to the magnetic recording medium and a recording and reproducing signal processing means for inputting a signal in the magnetic head and reproducing a signal outputted from the magnetic head. The magnetic recording medium has a strtrcture with a magnetic layer formed on a substrate by way of a monolayer or multilayer underlayer and the magnetic layer comprises magnetic crystal particles having a columnar structure or non- crystalline magnetic particles. The average particle diameter of the magnetic particles and particle size dispersion standardized by the average particle diameter are <=16nm and <=0.5, respectively. The value Ku.V/kT given by dividing the product of the magnetic anisotropy constant Ku and volume V of the magnetic particles by the product of the Boltzmann's constant k and absolute temperature T is >=60 and the thickness of the magnetic layer is <2 times the average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic storage device, and more particularly, to a magnetic storage device having a recording density of 2 gigabits per square inch or more, and a low noise and thermal fluctuation for realizing the same. And a thin film magnetic recording medium having sufficient stability.

[0002]

2. Description of the Related Art A demand for a large capacity of a magnetic storage device is increasing at present. Conventional magnetic heads use an electromagnetic induction type magnetic head that utilizes a voltage change accompanying a temporal change in magnetic flux. This is to perform both recording and reproduction with one head.

On the other hand, in recent years, a composite head using a magnetoresistive head, which has a high sensitivity as a reproducing head, separately from a recording head and a reproducing head, is rapidly progressing. The magnetoresistive head utilizes the fact that the electrical resistance of the head element changes with the change of magnetic flux leakage from the medium. Further, the development of a more sensitive head utilizing an extremely large magnetoresistance change (giant magnetoresistance effect or spin valve effect) generated in a magnetic layer of a type in which a plurality of magnetic layers are stacked via a nonmagnetic layer has been advanced. It is getting. This effect is an effect in which the relative directions of the magnetizations of the plurality of magnetic layers via the non-magnetic layer change due to the leakage magnetic field from the medium, thereby changing the electric resistance.

[0004] To increase the recording density, it is necessary to further reduce the noise of the recording medium. Computer simulations and experiments have shown that the reduction of exchange interaction between magnetic crystal grains and the miniaturization of magnetic crystal grains are effective in reducing medium noise (J. Appl. Phys. Vo
l. 63 (8), 3248 (1988); App
l. Phys. Vol. 79 (8), 5339 (1
996)). Specific methods for reducing the exchange interaction mainly include increasing the Cr concentration in the magnetic layer and increasing the degree of spatial separation of magnetic crystal grains. Higher Cr concentration segregates a larger amount of Cr at the crystal grain boundaries and reduces the exchange interaction between magnetic crystal grains. However, at the same time, the Cr concentration in the magnetic crystal grains also increases, which causes a decrease in the saturation magnetic flux density. In order to maintain the value of Br × t, which is the product of the residual magnetic flux density Br and the magnetic layer thickness t, the magnetic layer film is formed. It is necessary to increase the thickness. However, this method has a limit because crystal grains increase in thickness due to an increase in film thickness and increase in medium noise. Further, in order to increase the degree of separation of the magnetic crystal grains, it is necessary to sharpen the crystal grains of each underlayer having a columnar structure. For this purpose, it is necessary to increase the thickness of the underlayer, but in this case also, the magnetic crystal grains formed thereon are enlarged. Therefore, there is a limit to this method.

In Japanese Patent Application Laid-Open No. Hei 7-31929, an oxide such as SiO2 is added to a magnetic layer and segregated at the grain boundary to reduce exchange interaction between crystal grains and to suppress crystal growth. Measures for reducing the particle size have been proposed. However, since the addition of an insulator significantly increases the resistance value of the target, the film must be formed by RF sputtering. The RF sputtering method is inferior to the DC sputtering method in cost, stability, and the like, and is not suitable for mass production. Further, the medium manufactured by the RF sputtering method has a problem that it is difficult to control the crystal orientation, and thus it is difficult to obtain a high coercive force and a coercive force squareness ratio.

On the other hand, the fine magnetic crystal grains are more strongly affected by thermal fluctuations, so that the stability of recorded magnetization is significantly reduced. For this reason, the rate of occurrence of magnetization reversal increases with time, and sufficient reliability cannot be ensured for long-term data storage. Further, the refined crystal grains are more strongly affected by magnetostatic interaction from the adjacent crystal grains, which causes an increase in medium noise. Therefore, the crystal grains need to keep a certain size.

[0007]

As described above, in order to achieve a high recording density, a magnetic recording medium having not only low noise but also sufficient stability against thermal fluctuation is required.

[0008] An object of the present invention is to control the average grain size and the grain size dispersion of the magnetic crystal to values within appropriate ranges, thereby achieving low noise and having sufficient stability against thermal fluctuation. An object of the present invention is to provide a magnetic recording medium, and to provide a highly reliable magnetic storage device having a recording density of 2 gigabits per square inch or more by combining the magnetic recording medium with a highly sensitive magnetic head.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having a magnetic layer formed on a substrate with a single layer or a multi-layer underlayer, wherein the average grain size of crystal grains in the magnetic layer is smaller than
d> is set to 16 nm or less, and the particle size dispersion Δd / <d> (hereinafter, referred to as normalized particle size dispersion) standardized by the average particle size is set to 0.1.
It is achieved by setting it to 5 or less. Where the grain size,
The standardized particle size distribution is defined as follows. The area of each crystal grain is determined from the lattice image of the surface of the magnetic layer obtained by observation with a transmission electron microscope, and the diameter of a perfect circle having the same area is estimated, which is defined as the crystal grain size. At this time, when a structure in which a plurality of magnetic crystal grains are grown with different crystal orientations on the same base crystal grain, that is, a bicrystal structure is observed, a magnetic crystal having the same crystal orientation is counted as one crystal grain. Of the observed crystal grains, the value obtained by normalizing the total area of the crystal grains having a grain size equal to or smaller than the measured area of all the crystal grains is defined as an integrated area ratio. FIG. 1 shows the relationship between the magnetic crystal grain size of the medium and the integrated area ratio (hereinafter, referred to as an integrated area ratio curve) in the present invention. In the present invention, the particle size when the integrated area ratio becomes 50% is defined as an average particle size <d>,
The difference Dd between the particle size at which the integrated area ratio becomes 75% and the particle size at which the integrated area ratio becomes 25% is defined as the particle size dispersion width. Further, a ratio Dd / <d> between Δd and the average particle diameter is defined as a normalized particle diameter dispersion.

When the average particle size is larger than 16 nm, 20
When recording is performed at a high linear recording density of 0 kFCI or more, the disorder (irregularity) of the magnetization transition region increases, and the medium noise increases, which is not preferable. Further, when the normalized particle size distribution is 0.5 or more, the number of extremely fine crystal grains increases,
Since these are strongly affected by thermal fluctuations, the recording magnetization greatly decreases, which is not preferable. Further, at this time, the medium noise also increases, which is not preferable. In this way, not only miniaturization of magnetic crystal grains but also elimination of extremely fine crystal grains that are susceptible to thermal fluctuations by uniformizing not only noise reduction but also stability against thermal fluctuations It is extremely important to ensure the performance. As shown in Example 2, when the normalized particle size distribution is set to 0.4 or less, further reduction in noise and improvement in thermal stability are achieved, which is more preferable. In addition, such control of the magnetic crystal grain size is extremely effective for noise reduction especially for a medium using a glass substrate, which has been difficult to reduce noise compared to a medium using a NiP / Al substrate. Means.

As the magnetic layer, CoCrPt, CoCrP
tTa, CoCrPtTi, CoCrTa, CoNiC
An alloy containing Co as a main component and containing Cr, such as r, can be used. However, in order to obtain a high coercive force, a Co alloy containing Pt is preferably used. The product Ku · V of magnetic anisotropy energy Ku of magnetic crystal grains and volume V
Divided by the product of Boltzmann's constant k and absolute temperature T, K
By setting u · V / kT to 60 or more, the influence of thermal fluctuation can be reduced. When Ku · V / kT is less than this, the probability of magnetization reversal sharply increases due to the influence of thermal fluctuations, so that the attenuation of recording magnetization becomes remarkable,
Not preferred. In particular, for a medium in which the particle size of the magnetic layer is 10 nm or less, a high Pt concentration alloy or S
alloys containing rare earth elements such as mCo, FeSmN, etc.
It is desirable to use a u material. The thickness of the magnetic layer is preferably not more than 2.5 times the average particle size. When the film thickness is more than this, the shape magnetic anisotropy in the direction perpendicular to the film surface increases, and the coercive force in the film surface direction decreases, which is not preferable.

The magnetic properties of the magnetic layer are as follows: a coercive force measured by applying a magnetic field in the recording direction is 2 kOe or more;
If the product Br × T of the residual magnetic flux density Br and the film thickness t is 40 Gauss / micron or more and 140 Gauss / micron or less, 1
It is preferable because good recording / reproducing characteristics can be obtained in a recording density region of 2 gigabits per square inch or more. When the coercive force is smaller than 2 kOe, a high recording density (20
(0 kFCI or more), which is not preferable because the output becomes small.
Further, when Br × T is larger than 140 Gauss / micron, the resolution is reduced, and when it is smaller than 40 Gauss / micron, the reproduction output is undesirably reduced.

Further, carbon is formed to a thickness of 5 nm to 20 nm as a protective layer for the magnetic layer, and a lubricating layer made of adsorbable perfluoroalkyl polyether is formed to a thickness of 2 nm to 10 nm.
By providing nm, a magnetic recording medium with high reliability and capable of high-density recording can be obtained. Further, a carbon film to which hydrogen is added as a protective layer, a film made of silicon carbide, tungsten carbide, a compound such as (W—Mo) —C, (Zr—Nb) —N, or a film of these compounds and carbon It is preferable to use a mixed film because sliding resistance and corrosion resistance can be improved. In addition, after forming these protective layers, plasma etching is performed using a fine mask or the like to form fine irregularities on the surface, or a heterogeneous projection is formed on the surface of the protective layer using a compound or mixture target. Alternatively, it is preferable to form irregularities on the surface by heat treatment because the contact area between the head and the medium can be reduced, and the problem of the head sticking to the medium surface during CSS operation is preferable.

The magnetic recording medium, a drive unit for driving the magnetic recording medium in a recording direction, a magnetic head including a recording unit and a reproducing unit, a unit for moving the magnetic head relative to the magnetic recording medium, In a magnetic storage device having recording / reproduction signal processing means for performing signal input to a magnetic head and reproduction of an output signal from the magnetic head, by configuring a reproduction unit of the magnetic head by a magnetoresistive magnetic head, A sufficient signal intensity at a high recording density can be obtained, and a highly reliable magnetic storage device having a recording density of 2 gigabits per square inch or more can be realized. Further, the distance between two shield layers (shield distance) sandwiching the magnetoresistive sensor portion of the magnetoresistive head used in the magnetic recording apparatus of the present invention is preferably 0.30 μm or less. This is because when the shield interval is 0.30 μm or more, the resolution is reduced and the phase jitter of the signal is increased. Further, the magneto-resistance effect type magnetic head is composed of a plurality of conductive magnetic layers that generate a large resistance change due to a relative change in their magnetization directions due to an external magnetic field, and a conductive layer disposed between the conductive magnetic layers. By using a magnetoresistive sensor including a conductive nonmagnetic layer and utilizing the giant magnetoresistance effect or the spin valve effect, the signal strength can be further increased,
A highly reliable magnetic storage device having a recording density of 4 gigabits per square inch or more can be realized.

[0015]

<Embodiment 1> An embodiment of the present invention will be described with reference to FIGS. 2, 3 and 4. FIG. FIGS. 2A and 2A are a schematic plan view and a schematic sectional view of the magnetic storage device of the present embodiment.
(B). This device is a magnetic storage device having a known structure including a magnetic head 1, a drive unit 2 for the magnetic head, a recording / reproducing signal processing means 3 for the magnetic head, a magnetic recording medium 4, and a drive unit 5 for rotating the magnetic head. .

FIG. 3 shows the structure of the magnetic head. This magnetic head is a composite type head having both an electromagnetic induction type magnetic head for recording and a magnetoresistive magnetic head for reproduction formed on the base 6. The recording head is a coil 7
The upper recording magnetic pole 8 and the lower recording magnetic pole / upper shield layer 9 sandwiching the magnetic recording medium and the gap layer thickness between the recording magnetic poles was 0.3 μm.

Further, Cu having a thickness of 3 μm was used for the coil. The reproducing head comprises a magnetoresistive sensor 10 and electrode patterns 11 at both ends thereof.
It is sandwiched between a lower recording magnetic pole / upper shield layer having a thickness of m and the lower shield layer 12, and the distance between the shield layers is 0.25 μm.

FIG. 4 shows a sectional structure of the magnetoresistive sensor.
The signal detection region 13 of the magnetic sensor includes a portion in which a lateral bias layer 15, a separation layer 16, and a magnetoresistive ferromagnetic layer 17 are sequentially formed on a gap layer 14 of Al oxide. A 20 nm NiFe alloy was used for the magnetoresistive ferromagnetic layer. NiFeNb of 25 nm was used for the lateral bias layer.
Any ferromagnetic alloy such as Rh or the like having a relatively high electric resistance and good soft magnetic properties may be used. The lateral bias layer is magnetized in an in-plane direction (lateral direction) perpendicular to the current by a magnetic field generated by a sense current flowing through the magnetoresistive ferromagnetic layer, and applies a lateral bias magnetic field to the magnetoresistive ferromagnetic layer. As a result, a magnetic sensor showing a linear reproduction output with respect to the leakage magnetic field from the medium can be obtained.

The separation layer for preventing the shunt of the sense current from the magnetoresistive ferromagnetic layer is made of Ta having a relatively high electric resistance.
The film thickness was 5 nm.

At both ends of the signal detection area, there are tapered portions 18 formed into a tapered shape. The tapered portion includes a permanent magnet layer 19 for converting the magnetoresistive ferromagnetic layer into a single magnetic domain, and a pair of electrodes 11 formed thereon for extracting a signal.
Consists of The permanent magnet layer needs to have a large coercive force and the magnetization direction does not easily change.
A Pt alloy or the like is used.

FIG. 5 shows the layer structure of the magnetic recording medium of this embodiment. As the substrate 20, a super smooth Al alloy substrate coated with NiP plating (hereinafter referred to as Al substrate) was used. After being heated by a lamp heater, the Cr-20 at% Ti alloy underlayer 21 is removed by DC magnetron sputtering.
-20 at%, Co-21 at% Cr-10 at% Pt alloy magnetic layer 22 at 20 nm, and carbon protective film 23 at 10 n
m. Ar was used as a sputtering gas, and the gas pressure at the time of forming each layer was changed from 5 to 20 mTorr. As the lubricant 24, a material obtained by diluting a perfluoroalkyl polyether-based material with a fluorocarbon material was used.

[0022]

[Table 1]

Table 1 shows the values of coercive force, normalized medium noise, and Ku · V / kT of the medium prepared under the above conditions.
Here, the normalized medium noise kNd is a linear recording density 220
This is a value obtained by standardizing the medium noise measured under the conditions of kFCI and head flying height of 50 nm by the solitary reproduction wave and the square root of the track width. Ku · V / kT is an anisotropic magnetic field Hk obtained from the measurement of rotational history loss at room temperature, an anisotropic constant Ku obtained from the saturation magnetization Ms as Ku = Hk · Ms / 2, This is a value calculated using the volume V. V is a value obtained from the average particle size and the thickness of the magnetic layer. k and T are Boltzmann's constant and absolute temperature, respectively.

When the magnetic layers of these media were observed with a transmission electron microscope, the magnetic layers had a columnar structure.
No clear segregation phase was observed between the magnetic crystal grains.

FIG. 6 shows the average particle size and the normalized particle size dispersion obtained from the obtained TEM image (lattice image) by the above-mentioned method.
Shown in In all of the media B to D of the present examples, as shown in Table 1, the normalized particle size dispersion was 0.5 or less, and the ratio of the thickness of the magnetic layer to the average particle size was 2 or less. The normalized medium noise is 0.018 or less, and the coercive force is 2 kOe or more, which is sufficient for realizing a high recording density of 2 gigabits per square inch or more. On the other hand, the medium A having an average particle diameter of 16 nm or more has a remarkably high noise. As described above, in the media of this example, no clear grain boundary phase was observed in any of the media, and the X-ray diffraction patterns of each of the media showed a (11.0) diffraction peak from the magnetic layer and a lower Only the (200) diffraction peak from the formation was shown, and no significant difference was found in the crystal orientation. From this, it is considered that the high noise in the medium A is due to the influence of the crystal grain size. Therefore, in order to realize a high recording density of 2 gigabits per square inch or more, it is understood that the average particle size needs to be 16 nm or less.

Further, in order to examine the effect of thermal fluctuation, which is another problem in increasing the recording density, a measurement was made of the decay rate of the reproduction output with respect to time. FIG. 7 shows the results. Here, the decay rate of the reproduction output is a value ΔS / obtained by normalizing the difference ΔS (= S1−S0) between the reproduction output S1 measured after standing for a certain period of time in the air at room temperature and the reproduction output S0 measured immediately after recording with S0. S0, which is considered to be a value indicating the stability of the medium with respect to thermal fluctuation. The linear recording density at this time was 220 kFCI. Each of the mediums A to D in the present embodiment is 9
The decay rate after 6 hours was within 2%. In this case, 10
The decay rate when extrapolated until the year after (8.76 × 104 hours) is estimated to be 5% or less, and is considered to be sufficiently suitable for long-term recording. On the other hand, Ku · V / kT is 60
The medium E of less than the above has a large output decay rate, indicating that the thermal stability is insufficient. Therefore, it is understood that Ku · V / kT needs to be 60 or more in order to obtain sufficient thermal stability.

In a magnetic storage device incorporating the medium of the present embodiment together with the above-described head, a CSS test (contact and
Start-stop test), 30,000 times C
Even when SS was performed, the coefficient of friction was 0.3 or less. Also,
The number of bit errors after 50,000 head seek tests from the inner circumference to the outer circumference of the medium was 10 bits / plane or less, and an average failure interval of 300,000 hours or more was achieved. <Embodiment 2> 10 nm Cr for the first underlayer and 5-20 nm (Cr-15at% Ti) -xa for the second underlayer.
Using a t% B alloy, a magnetic recording medium was manufactured in which the B concentration x was changed from 0 to 10 at%. 18 nm for the magnetic layer
Co-18at% Cr-14at% Pt-2at% T
a alloy was used.

Table 2 shows the magnetic characteristics of each medium.

[0029]

[Table 2]

Here, the normalized medium noise and the decay rate of the reproduction output are measured under the same conditions as in the first embodiment, and the decay rate is a value after 96 hours. As a result of obtaining the average particle size and the normalized particle size dispersion from the TEM image (lattice image), as shown in FIG. 8, the average particle size was 16 nm or less for all the media, and the ratio of the thickness of the magnetic layer to the average particle size was shown. Was 2 or less. Media B and D having a normalized particle size dispersion of 0.5 or more have an average particle size of Ku ·
Despite being in the region where V / kT> 60, the normalized medium noise is extremely high. These media also have large output attenuation rates of -4.2% and -5.6%, respectively. TE
In the M images, no clear grain boundary phase was observed in any of the media, and it is considered that there is no significant difference in the segregation state of each medium. Also, X
As a result of the line diffraction, in each medium, only the (200) diffraction peak of the body-centered cubic structure was observed from the first and second underlayers, and only the (11.0) diffraction peak of the hexagonal dense structure was observed from the magnetic layer. Was seen. Thus, the segregation state of the medium of the present embodiment,
Since there is no significant difference in the crystal orientation, it is considered that the difference in the magnetic properties described above is mainly caused by the uniformity of the magnetic crystal grains. Therefore, in order to obtain sufficient magnetic properties and thermal stability for high-density recording of 2 gigabits per square inch or more, it is necessary to produce a uniform medium having a normalized particle size distribution of 0.5 or less. I understand. Further, the medium E having a normalized particle size dispersion of 0.4 or less has extremely low noise and a low output decay rate although the average particle size is almost the same as that of the medium F. . From this, it can be seen that reducing the normalized particle size dispersion to 0.4 or less is extremely effective for further reducing noise and improving thermal stability.

In this embodiment, all the films are formed by the DC sputtering method, but the same effect can be obtained by other methods such as the ion beam sputtering method and the ECR sputtering method.

<Embodiment 3> In a magnetic storage device having the same configuration as in Embodiment 1, a magnetic recording medium using a Fe-Sm-N alloy for the magnetic layer was manufactured.

A CrB underlayer is formed to a thickness of 10 nm on a chemically strengthened soda lime glass substrate, and the B concentration is set to 0 to 10 a.
t%. The substrate is 3
After heating to 00 ° C., a magnetic layer of 12 nm FeSmN alloy and a carbon protective film were sequentially formed. An Fe-87 at% Sm-2 at% N alloy was used as the magnetic target. As a sputtering gas, a mixed gas obtained by adding 3% of nitrogen to Ar was used, and the gas pressure was 5 to 20 mTorr.

As a result of TEM observation, the structure of the magnetic layer of each medium had a columnar structure similar to that of Example 1. However, the magnetic particles were amorphous, and this structure was surrounded by a crystalline segregation phase. It turned out to be.

Table 3 shows the magnetic characteristics of each medium, and FIG. 9 shows the average particle size and normalized particle size distribution of the amorphous magnetic particles estimated by the same method as in Example 1.

[0036]

[Table 3]

All of these media have an average particle size of 16 nm or less, a standardized particle size dispersion of 0.5 or less, and a magnetic layer thickness of 2 or less with respect to the average particle size. Since a rare earth alloy having high crystal magnetic anisotropy is used for the magnetic layer, a Ku · V / kT of 60 or more is obtained even with a finer grain size than the media of Examples 1 and 2. Media A to C having Ku · V / kT of 60 or more
Has a high coercive force of 2 kOe or more, a low normalized medium noise of 0.018 or less, and an attenuation rate after 96 hours is 2
%, And sufficient characteristics for realizing a high recording density of 2 gigabits per square inch or more. However, since the medium D has a low Ku · V / kT of 56, the output attenuation rate is large and the thermal stability is poor. Again, Ku · V / kT is 6 in order to obtain sufficient stability against thermal fluctuation.
It is shown that it needs to be 0 or more.

When the recording / reproducing characteristics were evaluated using the magnetic storage device of this embodiment under the conditions of a head flying height of 30 nm, a linear recording density of 196 kBPI, and a track density of 10.5 kTPI, an apparatus S / N of 1.6 was obtained. Was. Further, by performing 8-9 code modulation processing on the input signal to the magnetic head and performing maximum likelihood decoding processing on the output signal, information of 2 gigabits per square inch could be recorded and reproduced. Moreover,
The number of bit errors after 50,000 head seek tests from the inner circumference to the outer circumference was 10 bits / plane or less, and 200,000 hours could be achieved at an average failure interval.

<Embodiment 4> In a magnetic storage device similar to that of Embodiment 1, a sensor shown in FIG. 10 was used as a reproducing magnetic head.

This sensor has a thickness of 5 nm on the gap layer 14.
Ta buffer layer 25, 7 nm first magnetic layer 26,
1.5 nm Cu intermediate layer 27, 3 nm second magnetic layer 2
8, 10 nm Fe-50 at% Mn antiferromagnetic alloy layer 2
Reference numeral 9 denotes a structure formed sequentially. A Ni-20 at% Fe alloy was used for the first magnetic layer, and Co was used for the second magnetic layer. The magnetization of the second magnetic layer is fixed in one direction by the exchange magnetic field from the antiferromagnetic layer. On the other hand, the direction of magnetization of the first magnetic layer, which is in contact with the second magnetic layer via the non-magnetic layer, changes due to the leakage magnetic field from the magnetic recording medium, so that a resistance change occurs. Such a change in resistance due to a change in the relative direction of magnetization of the two magnetic layers is called a spin valve effect. In this embodiment, a spin valve magnetic head utilizing this effect was used as a reproducing head. The tapered portion has the same configuration as the magnetic sensor of the first embodiment.

As a first underlayer on a glass substrate, Co-
Using a 30 at% Cr-10 at% Zr alloy, a Cr-15 at% Mo alloy for the second underlayer, and a Co-2 for the magnetic layer.
A magnetic recording medium using 0 at% Cr-12 at% Pt-2 at% Ta was used. The thickness of the underlayer and the film formation conditions are all constant, and only the thickness of the magnetic layer is 4 n from 16 to 36 nm.
Changed in m increments.

[0042]

[Table 4]

As shown in Table 4, all of the media were all Ku.
-V / kT was 60 or more. The average particle size is 16n
m or less, and the normalized particle size distribution was 0.5 or less (FIG. 1).
1). The magnetic layer thickness of each medium is 36 nm for the medium A, decreases by 4 nm below the medium B, and 16 nm for the medium E. Each of the media A and B had a coercive force of 2.4 kOe or less and a normalized medium noise of 0.018 or more when recorded at a linear recording density of 260 kFCI. These media are inadequate for high recording densities of 4 gigabits per square inch or more. This is because the ratio of the thickness of the magnetic layer to the average particle size of both media is 2.2, 2.1 and 2 respectively.
This is probably because the shape magnetic anisotropy in the direction perpendicular to the film was increased due to the larger size. Therefore, in order to obtain good magnetic properties, the thickness of the magnetic layer is preferably not more than twice the average particle size.

After a lubricant was applied to the medium, the medium was incorporated into an apparatus using the above-described head, and a linear recording density of 245 kBP was applied.
I, when the recording / reproducing characteristics were performed under the conditions of a track density of 16.5 kTPI, a high value of S / N = 1.8 was obtained. By subjecting the input signal to the magnetic head to 16-17 code modulation and applying the maximum likelihood decoding to the output signal, information of 4 gigabits per square inch could be recorded and reproduced. The number of bit errors after 50,000 head seek tests from the inner circumference to the outer circumference of the medium is 10 bits.
/ Plane, and 300,000 hours or more were achieved at the average failure interval.

[0045]

The magnetic recording medium of the present invention has the effects of reducing medium noise and improving stability against thermal fluctuation.
By using the magnetic recording medium and the magnetoresistive head of the present invention, a magnetic storage device having a recording density of 2 gigabits per square inch and an average number of failures of 300,000 hours or more can be realized.

[Brief description of the drawings]

FIGS. 1A and 1B are curves respectively showing the relationship between the average grain size of magnetic crystal grains, the integrated area ratio, and the integrated area in the magnetic recording medium of one embodiment of the present invention.

FIGS. 2A and 2B are a schematic plan view and a sectional view taken along line AA ′ of a magnetic storage device according to an embodiment of the present invention, respectively.

FIG. 3 is a perspective view showing an example of a cross-sectional structure of a magnetic head in the magnetic storage device of the present invention.

FIG. 4 is a schematic diagram showing an example of a cross-sectional structure of a magnetoresistive sensor section of a magnetic head in the magnetic storage device of the present invention.

FIG. 5 is a schematic diagram showing an example of a cross-sectional structure of a magnetic recording medium according to the present invention.

FIG. 6 is a map showing the relationship between the average grain size of magnetic crystal grains and the normalized grain size distribution in the magnetic recording medium of one embodiment of the present invention.

FIG. 7 is a diagram showing an attenuation rate with respect to time of a reproduction output of the magnetic recording medium according to one embodiment of the present invention.

FIG. 8 is a map showing the relationship between the average grain size of magnetic crystal grains and the normalized grain size distribution in the magnetic recording medium of one embodiment of the present invention.

FIG. 9 is a map showing the relationship between the average grain size of magnetic crystal grains and the normalized grain size distribution in the magnetic recording medium of one embodiment of the present invention.

FIG. 10 is a perspective view showing an example of a cross-sectional structure of a magnetic head in the magnetic storage device of the present invention.

FIG. 11 is a map showing the relationship between the average grain size of magnetic crystal grains and the normalized grain size distribution in the magnetic recording medium of one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic head, 2 ... Magnetic head drive part, 3 ... Recording / reproduction signal processing system, 4 ... Air recording medium, 5 ... Magnetic recording medium drive part, 6 ... Substrate, 7 ... coil, 8 ... upper recording magnetic pole, 9 ... lower recording pole and upper shield layer, 10 ... magnetic resistance sensor, 11 ... conductor layer, 12 ... lower shield layer,
13 ... signal detection area, 14 ... gap layer between shield layer and magnetoresistive sensor, 15 ... lateral bias layer, 16 ...
Separation layer, 17 ... Magnetoresistance ferromagnetic layer, 18 ... Tapered portion, 19 ... Permanent magnet layer, 20 ... Substrate, 21 ... Underlayer,
22 ... magnetic layer, 23 ... protective film, 24 ... lubricating film, 2
5 ... buffer layer, 26 ... first magnetic layer, 27 ... intermediate layer, 28 ... second magnetic layer, 29 ... antiferromagnetic layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Ishikawa 2880 Kozu, Odawara-shi, Kanagawa Prefecture, Hitachi, Ltd.Storage Systems Division (72) Inventor Ichiro Tamai 1-1280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Joe Hosoe 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside Hitachi, Ltd.Central Research Laboratory (72) Inventor Yoshifumi Matsuda 2880 Kokuzu, Odawara-shi, Kanagawa Prefecture Storage Systems Division, Hitachi, Ltd. 72) Inventor Toru Tanahashi 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tomoki Yamamoto 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (8)

[Claims] 1. A magnetic recording medium having a magnetic layer formed on a substrate via a single-layer or multi-layer underlayer, a driving unit for driving the magnetic layer in a recording direction, and a magnetic unit having a recording unit and a reproducing unit. A magnetic head having means for moving the magnetic head relative to the recording medium, and processing means for recording / reproducing signals input / output via the magnetic head, wherein the magnetic layer has a columnar structure. The average particle diameter <d> of the magnetic particles measured in a plane parallel to the substrate surface is 16 nm or less, and the ratio of the particle diameter dispersion width Δd to the average particle diameter Δd / <
d> 0.5 or less. 2. A magnetic recording medium having a magnetic layer formed on a substrate via a single-layer or multi-layer underlayer, a driving unit for driving the magnetic layer in a recording direction, and a magnetic unit comprising a recording unit and a reproducing unit. A head, means for causing the magnetic head to move relative to the recording medium, and means for processing a recording / reproducing signal input / output via the magnetic head, wherein the magnetic layer has a columnar structure A region, which is composed of crystalline magnetic particles and is observed as having the same crystal orientation in the lattice image of the magnetic layer by a transmission electron microscope, is defined as a crystal grain and is defined by a diameter of a perfect circle having the same area as the observed region. The integrated area ratio obtained by standardizing the value obtained by integrating the area of the crystal grain calculated from the particle size of the crystal grain with respect to the particle size is 50 % Defined as particle size Diameter <d> is not more than 16 nm, the particle size dispersion width Δd to be defined by the difference between the particle size the integrated area ratio is the particle diameter and the 25% to be 75%, the average particle size <
A magnetic storage device characterized in that a value normalized by d> and a normalized average particle size variance defined as Δd / <d> are 0.5 or less. 3. A magnetic recording medium having a magnetic layer formed on a substrate via a single-layer or multi-layer underlayer, a drive unit for driving the magnetic layer in a recording direction, and a magnetic unit comprising a recording unit and a reproducing unit. A head, means for causing the magnetic head to move relative to the recording medium, and means for processing a recording / reproducing signal input / output via the magnetic head, wherein the magnetic layer has a columnar structure A region composed of amorphous magnetic particles and defined as having a same crystal orientation in a lattice image of the magnetic layer by a transmission electron microscope is defined as a crystal grain and defined as a diameter of a perfect circle having the same area as the observed region. The integrated area ratio obtained by standardizing the value obtained by integrating the area of the crystal grain calculated from the particle size of the crystal grain with respect to the particle size as the integrated area of all the observed crystal grains Average defined as particle size at 50% Diameter <d> is not more than 16 nm, the particle size dispersion width Δd to be defined by the difference between the particle size the integrated area ratio is the particle diameter and the 25% to be 75%, the average particle size <
A magnetic storage device characterized in that a value normalized by d> and a normalized average particle size variance defined as Δd / <d> are 0.5 or less. 4. The method according to claim 1, wherein said normalized average particle size distribution / <d> is 0.1.
The magnetic storage device according to any one of claims 1 to 3, wherein the number is 4 or less. 5. The magnetic storage device according to claim 1, wherein a product of an anisotropy constant Ku and an average volume V of said magnetic particles is a product of a Boltzmann constant k and an absolute temperature T. A magnetic storage device, wherein a value KuV / kT divided by a product is 60 or more. 6. The magnetic storage device according to claim 1, wherein an anisotropy magnetic field HK and a saturation magnetization Ms obtained from a measurement of a rotational history loss at room temperature are used.
It is expressed by an anisotropy constant Ku defined as K · Ms / 2, an average volume V of crystal grains calculated from the average grain size and the thickness of the magnetic layer, a Boltzmann constant k, and an absolute temperature T. A magnetic storage device having a value KuV / kT of 60 or more. 7. The magnetic memory device according to claim 1, wherein the magnetic layer contains a magnetic alloy having a hexagonal close-packed structure, and the c-axis of the magnetic particles is substantially in the plane of the substrate. In the body-centered cubic structure, wherein the magnetic layer is oriented so that the (100) plane is substantially parallel to the substrate surface.
A magnetic storage device characterized by being formed on a base layer mainly composed of: 8. The magnetic storage device according to claim 7, wherein
The magnetic alloy contains 15 to 23 at% of Cr and 6 to 20 at%.
% Pt.