JP3294231B2 - Magnetic recording device and magnetic recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording apparatus and a magnetic recording method for magnetically recording and reproducing information.

[0002]

2. Description of the Related Art With the recent increase in processing speed of computers, magnetic recording devices (HDs) for recording and reproducing information have been developed.
D) requires high speed and high density. But,
Densification has physical limitations.

In a magnetic recording apparatus, it is necessary to reduce magnetic domains recorded in a recording layer in order to perform high-density recording. In order to be able to separate small recording magnetic domains, it is necessary that the boundaries between the magnetic domains are smooth, and for that purpose, it is necessary to reduce the size of the magnetic particles constituting the recording layer. In order to perform high-density recording, it is necessary to reduce the thickness of the recording layer, and it is also necessary to reduce the size of the magnetic particles. However, when the magnetic particles are miniaturized, the magnetic anisotropy energy of the magnetic particles (magnetic anisotropy energy density Ku × volume of the magnetic particles)
However, there is a risk that the energy becomes smaller than the thermal fluctuation energy.
When the energy of the magnetic particles becomes smaller than the thermal fluctuation energy, the magnetization reversal of the recording magnetic domain occurs, and the recording can no longer be held. This is called the thermal fluctuation limit, or super-paramagnetic limit. In order to prevent magnetization reversal due to thermal fluctuation, it is conceivable to use magnetic particles having a large Ku. However, when Ku of the magnetic particles increases, the coercive force of the magnetic particles increases in proportion to Ku. Therefore, the magnetization cannot be reversed by the magnetic field generated by the recording head, and there is a possibility that recording cannot be performed.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording apparatus and a magnetic recording method capable of high-density recording exceeding a thermal fluctuation limit.

[0005]

A magnetic recording apparatus according to the present invention comprises a magnetic recording medium having a recording layer formed on a substrate, a means for heating the recording layer, and a means for applying a magnetic field to the recording layer. The magnetic recording medium, the heating means, and the magnetic field applying means, wherein the magnetic anisotropy energy density Ku (T) at the temperature T of the recording layer and the density Ku (T
Ratio with a): RKu (T) = Ku (T) / Ku (Ta)
Are characterized by satisfying the relationship of T / RKu <11200 / (ln (t) +20.72) with respect to the elapsed time t after the application of the magnetic field.

[0006] In the magnetic recording apparatus of the present invention, the coercive force of the recording layer is preferably at least 4 kOe at room temperature.

A magnetic recording method according to the present invention is a magnetic recording method for a magnetic recording medium in which a recording layer composed of magnetic particles and a non-magnetic material interposed therebetween is formed on a substrate, The method includes a step of heating the recording layer and a step of recording by applying a magnetic field to the recording layer, wherein the value of the magnetic anisotropy energy density of the recording layer at a temperature T is Ku (T) and the value at a room temperature Ta is The value is Ku (Ta) and the ratio of these values is RKu (T) = K
u (T) / Ku (Ta), the ratio RKu
(T) and the elapsed time t after the end of the application of the magnetic field satisfies the relationship of T / RKu <11200 / (ln (t) +20.72).

[0008] In the present invention, for example, in the above heating step RKu of a maximum temperature T _max (T _{m ax)} is heated so that 0.01 or less, the recording 1ns or 50ns within the time the maximum temperature reached in step To complete the recording operation.

In the present invention, the recording layer is heated so that RKu (T) of the recording layer becomes 0 before reaching the maximum temperature in the heating step.
A method of completing the recording operation within 0 ns to 100 ns may be used.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic recording apparatus according to the present invention includes a magnetic recording medium, a heating unit, and a magnetic field applying unit. In the apparatus of the present invention, after the recording layer of the magnetic recording medium is heated by the heating means, recording is performed by applying a magnetic field by the magnetic field applying means. This method uses heat-assisted recording (th
ermal assisted recording). Since the coercive force Hc decreases when the temperature of the magnetic material increases, magnetic recording can be performed by easily reversing the magnetic domain by applying a magnetic field. The magnetic recording apparatus according to the present invention can perform magnetic recording even on a magnetic material having a coercive force Hc of 4 kOe or more at room temperature, which cannot be conventionally recorded.

The magnetic recording medium according to the present invention has a structure in which a recording layer composed of magnetic particles and a non-magnetic material interposed between the magnetic particles is formed on a substrate. Also,
An underlayer may be provided between the substrate and the recording layer, or a protective layer may be provided on the recording layer.

The substrate is for supporting the recording layer, and is made of metal, glass, ceramic, or the like.

The recording layer is a so-called multi-particle layer composed of magnetic particles and a non-magnetic material interposed between the magnetic particles. The recording layer having such a structure can be formed as follows. For example, when a magnetic material is deposited on a substrate by sputtering, as in the case of forming a recording layer of a normal hard disk, a columnar magnetic crystal grows, and a non-magnetic element precipitates around the magnetic crystal, thereby forming a magnetic particle. A non-magnetic material (grain boundary) interposed between the magnetic particles is formed.

After a continuous film of an amorphous magnetic material is formed on a substrate, the film may be processed to form columnar magnetic particles. After a non-magnetic material is formed on the entire surface of the substrate, the surface is polished, whereby a structure in which the non-magnetic material is interposed between the magnetic particles can be formed. Further, a structure in which a non-magnetic material is interposed between magnetic particles can be formed only by applying a lubricant to the entire surface of the substrate.

The material for forming the recording layer includes a saturation magnetization Is.
A magnetic material having a large magnetic anisotropy is suitable. As the magnetic material, for example, Co, Pt, Sm, F
At least one magnetic metal material selected from the group consisting of metals such as e, Ni, Cr, Mn, Bi, and Al, and alloys of these metals. Among these magnetic metal materials, a Co-based alloy having a large crystal magnetic anisotropy, particularly a material based on CoPt, SmCo, or CoCr is more preferable. Specifically, Co-Cr, Co
-Pt, Co-Cr-Ta, Co-Cr-Pt, Co-
Cr-Ta-Pt, Co, Fe and the like.

Further, as the magnetic material, an amorphous rare earth element is used.
Transition metal alloys such as Tb-Fe, Tb-Fe-C
o, Tb-Co, Gd-Tb-Fe-Co, Gd-Dy
-Fe-Co, Nd-Fe-Co, Nd-Tb-Fe-
Co; an ordered alloy such as PtMnSb, FePt; a magnetic oxide such as Co ferrite or Ba ferrite may be used.

For the purpose of controlling magnetic properties such as saturation magnetization and coercive force, at least one element selected from the group consisting of Fe and Ni may be added to the above magnetic material. Additives for improving magnetic properties, such as Cr, Nb, V, Ta, Ti, W, Hf, and C, are added to these magnetic materials.
r, V, In, Si, B, or the like, or a compound of these elements and at least one element selected from oxygen, nitrogen, carbon, and hydrogen may be added.

The recording layer may have in-plane magnetic anisotropy like a recording layer of a hard disk, or may have perpendicular magnetic anisotropy like a recording layer of a magneto-optical recording medium. Good.

The underlayer may be magnetic or non-magnetic.
The underlayer made of a magnetic material is magnetically coupled to the magnetic domain of the recording layer by an exchange coupling interaction or a magnetostatic coupling interaction. When a magnetic underlayer having a large coercive force is provided and exchange-coupled with a magnetic domain of the magnetic layer, the magnetic domain can be stabilized. When a magnetic underlayer having a large magnetization is provided and exchange-coupled with a magnetic domain of the recording layer, an output signal can be increased.

The underlayer made of a non-magnetic material is provided for the purpose of controlling the crystallinity of the recording layer or the purpose of preventing impurities from entering the recording layer from the substrate. For example, by using an underlayer having a lattice spacing close to the crystal lattice spacing of the recording layer, it is possible to control the crystallinity of the magnetic part. Examples of such an underlayer include Cr and the like.
Also, for example, when an amorphous underlayer is used, the recording layer can generally be made amorphous. In order to prevent impurities from entering the recording layer from the substrate, it is preferable to use a thin film having a small lattice spacing or a dense film as the underlayer.

Further, the magnetic underlayer may have the function of the above-mentioned nonmagnetic underlayer. For example, the magnetic underlayer may have a function of controlling the crystallinity of the recording layer.
In this case, the effect of improving the recording / reproducing characteristics and the effect of improving the crystallinity can be simultaneously obtained. Examples of such an underlayer include an underlayer made of amorphous CoZrNb.

The underlayer may be a surface modified layer of the substrate. The surface modified layer is obtained by ion plating, doping of gas components, neutron irradiation, or the like. In this case, the process of forming the underlayer can be omitted.

As the protective layer, for example, carbon, Si
N, SiO ₂ , Au, or a laminate thereof is used.

The heating means may be a means for heating the entire surface of the recording medium uniformly or a means for locally heating the recording medium.
In general, when a high-density magnetic recording medium is heated, the effect of thermal fluctuations is exerted and the recording retention characteristics are deteriorated. Therefore, it is preferable to locally heat the medium and keep most of the medium at room temperature. However, in a recording apparatus using a medium in which the recording retention characteristics do not deteriorate even when the entire surface of the recording medium is heated, heating the entire surface may be preferable because the cost can be reduced.

Examples of the heating means capable of high-speed and local heating include heating by a laser used in an optical disk, induction heating, and heating by a probe heated by a heating wire or the like. In order to perform more localized heating, a method of heating the laser beam by focusing it on the medium surface with a lens or the like, a method of forming a fine antenna at the tip of the probe and performing induction heating from the antenna,
It is possible to use a method in which the shape of the medium facing surface of the heating probe is made as sharp as possible or the distance from the medium is made shorter to heat the probe. The heating means as described above may be arranged on the recording surface side of the medium or on the side opposite to the recording surface.

As the magnetic field applying means, an ordinary recording head can be used. The recording head forms a magnetic circuit including a magnetic pole and an induction coil. As the magnetic field applying means, a permanent magnet may be used. When a permanent magnet is used, the distance between the permanent magnet and the recording medium is made variable,
Alternatively, a high-resolution magnetic field can be applied at high speed by devising a method such as miniaturizing the permanent magnet. Further, as the magnetic field applying means, another magnetic layer laminated with the recording layer may be used. By heating or light irradiation, the added magnetic layer has a temperature distribution to generate a magnetization distribution, and a magnetic field can be applied to the recording layer. Further, a leakage magnetic field generated from the magnetic layer may be applied to the recording layer as a recording magnetic field.

An example of the magnetic recording apparatus according to the present invention will be described with reference to FIG. In FIG. 1, a magnetic recording medium 10
Are formed on a disk substrate 11 with an underlayer 12, a recording layer 13,
And a protective layer 14 is laminated. This magnetic recording medium 10 rotates in the direction indicated by A in the figure.

A slider 20 is disposed on the recording medium 10, and a recording / reproducing element 30 is provided on an end face of the slider 20. The recording element portion of the recording / reproducing element 30 corresponds to a magnetic field applying unit. In addition, slider 20
Is provided with an optical waveguide 40 for transmitting a laser beam, and a laser beam is applied to the medium 10 from an end 41 of the optical waveguide 40. The slider 20 is a magnetic recording medium 1
It floats by rotation of 0. The optical waveguide 40 and the recording / reproducing element 30 are arranged such that the recording layer 13 is heated by irradiating the recording layer 13 with a laser beam irradiated from the end 41 of the optical waveguide 40, and then a magnetic field is applied to the recording layer 13 by the recording element. Have been.

In the magnetic recording apparatus according to the present invention, the temperature and the magnetic characteristics of the recording layer are expressed by the following relational expression (1) with respect to the elapsed time t after the end of the application of the magnetic field to the recording layer (after the end of recording). Is performed so as to satisfy the following.

T / RKu (T) <11200 / (ln (t) +20.72) (1) where T is the temperature of the recording layer. RKu (T) is a value Ku at the temperature T of the magnetic anisotropy energy density of the recording layer.
The ratio between (T) and the value Ku (Ta) at room temperature Ta, that is, Ku (T) / Ku (Ta). If the recording layer satisfies the condition of the expression (1), even if the recording layer is composed of magnetic particles having a small size and a high coercive force, a uniform and clear magnetic domain is formed in the recording layer. Can be formed. As a result, high-density magnetic recording exceeding the thermal fluctuation limit becomes possible.

Hereinafter, the relationship of the above equation (1) will be described in more detail.

Of the physical properties related to the magnetization reversal of the recording layer,
A magnetic property that greatly changes with temperature is a magnetic anisotropy energy density Ku. Magnetic anisotropy energy density Ku
Decreases monotonically with an increase in the temperature T. Coercive force Hc
Is generally proportional to Ku, and thus also decreases as the temperature T increases. Further, T / RKu (T) in the equation (1) monotonically increases as the temperature T increases. FIG. 2 shows a qualitative relationship between these functions.

First, the present inventors simulated the temperature response by irradiating a recording medium having a laminated structure of thin films as shown in FIG. 1 with a laser beam. as a result,
It was found that the reciprocal 1 / T of the temperature T of the recording medium and the logarithm ln (t) of the elapsed time t after the application of the magnetic field showed a simple relationship. FIG. 3 shows the reciprocal 1 / T of the temperature T of the recording medium,
An example of the relationship between the elapsed time t after the application of the magnetic field and the logarithm ln (t) is shown. As is apparent from this figure, 1 / T and ln (t) are used at the beginning and the end of the cooling process of the recording medium, respectively.
Are almost proportional to each other, and the relationship between the two can be approximated by two straight lines (broken lines in the figure). Therefore, recording is performed under various conditions in which the temperature response of the recording layer is different, and the recording state is changed to ln.
It was presumed that, by examining in connection with (t), it is possible to know the conditions for obtaining a complete recording state even when it is unknown at which point in the process of cooling the medium the magnetization reversal occurs.

As described above, the change in the magnetic anisotropy energy density Ku closely related to the magnetization reversal of the recording layer changes monotonically with T. However, when the recording layer is cooled, T and Ku
Since both of these variables change, it is difficult to associate each of these variables alone with the recording state. Thus, we have found that Ku / T as a function of decreasing with temperature,
Or a function RK that standardizes this function with the value of Ku at room temperature
It has been found useful to correlate u / T with ln (t).

Based on the above prediction, a recording / reproducing experiment was actually performed as follows. As the magnetic recording medium 10 shown in FIG.
On top of this, Cr having a thickness of 70 nm as the underlayer 12 and the recording layer 1 were formed.
As No. 3, a layer of CoPtCr having a thickness of 20 nm and a layer of carbon having a thickness of 10 nm as the protective layer 14 were used. C
Ku of the recording layer 13 made of oPtCr at room temperature is 8 × 1
0 ⁶ erg / cc, the coercive force was 4kOe.

The magnetic recording medium 10 is rotated at 4500 rpm in the direction of arrow A, and the flying height of the slider 20 is reduced to 8
It was set to 0 nm. A wavelength of 650 nm and an output of 3 m from a semiconductor laser (not shown) through the end 41 of the optical waveguide 40
While continuously irradiating the medium 10 with the laser beam of W,
A recording frequency of 200 kfci is applied by applying a magnetic field from the recording element.
Recorded. The beam spot diameter on the medium surface is 2 at half width.
μm. The recording track width was 2 μm. The recording state of the medium was confirmed by magnetic domain observation using a magnetic force microscope (MFM).

When the recording medium was not irradiated with a laser beam by this apparatus, no clear magnetic domain could be confirmed.
On the other hand, it was confirmed that a magnetic domain was formed by irradiating the recording medium with the laser beam under the above conditions.

Further, in order to examine the conditions under which magnetic domains are formed, recording was performed under various rotational speeds of the medium and heating conditions using a laser beam. Then, magnetic domains of the medium were observed by MFM, and it was examined whether uniform and clear magnetic domains were formed.

Here, the value of Ku (T) of the medium was obtained by measurement, and RKu (T) was calculated. The temperature of the medium was obtained by simulation.

FIG. 4 shows an experimental result in a coordinate system of RKu / T and ln (t). In FIG. 4, white circles indicate the case where magnetic domains could be formed, and black circles indicate the case where magnetic domains could not be formed. It can be seen that recording is possible in an area above the straight line shown in FIG. This relationship is expressed as RKu (T) / T> (ln (t) +20.72) / 11200 (2).

FIG. 5 shows an experimental result in a coordinate system of T / RKu and the elapsed time t after recording to make it easier to understand the relationship that the temperature T decreases with the elapsed time t. Also in this figure, white circles indicate the case where magnetic domains could be formed, and black circles indicate the case where magnetic domains could not be formed. FIG. 5 shows that recording is possible in the area below the curve. This relationship is obtained by reversing the denominator and the numerator of the equation (2), and is expressed as T / RKu (T) <11200 / (ln (t) +20.72) (1). As described above, if the condition of Expression (1) is satisfied,
Magnetic domains are formed in the recording layer.

In the same manner as described above, heating and magnetic recording of the medium were performed under the four conditions, and RKu /
The change in T was tracked. The four conditions are selected near the boundary in FIG. FIG. 6 shows experimental results in a coordinate system of RKu / T and ln (t). The four marks in FIG. 6 correspond to four conditions. Also in FIG. 6, white circles indicate conditions under which magnetic domains could be formed, and black circles indicate conditions under which magnetic domains could not be formed. The area above the straight line in FIG. 6 is represented by the above equation (2). FIG. 6 shows that if there is a time that does not satisfy the condition of the expression (2) even temporarily after recording, no magnetic domain is formed in the recording layer under that condition.

FIG. 7 shows an experimental result in a coordinate system of T / RKu and the elapsed time t after recording in order to easily understand the relationship that the temperature T decreases with the elapsed time t. In this figure, the description of each mark is the same as that in FIG. In FIG.
The area below the curve is represented by the above equation (1). FIG.
If there is a time that does not satisfy the condition of Expression (1) even temporarily after recording, it indicates that no magnetic domain is formed in the recording layer under that condition. Therefore, it can be concluded that the condition of Expression (1) must always be satisfied in the cooling process after recording.

In the magnetic recording apparatus according to the present invention, the magnetic recording medium, the heating means, and the magnetic field applying means are configured so that a recording operation satisfying the above equation (1) is performed. Therefore, factors to be considered for satisfying the condition of the expression (1) will be described.

The manner of changing the temperature of the recording layer can be controlled as follows. For example, as employed in an optical recording medium, it is conceivable to use a medium provided with a heat sink layer having a high thermal conductivity or a heat insulating layer made of a dielectric material having a low thermal conductivity in the vicinity of the recording layer. . By providing the heat sink layer, the rate at which the temperature T of the recording layer changes with respect to time t (dT / dt) can be increased to realize a steep temperature change. Examples of the material of the heat sink layer include a conductive material such as Ag. On the other hand, by providing the heat insulating layer, (dT / dt) can be reduced and a gradual temperature change can be realized. As a material of the heat insulating layer, for example, a dielectric such as SiO ₂ can be used.
Further, by arranging the heat sink layer and the dielectric layer in combination, it is possible to design a desired temperature change for the recording layer. Such a medium can be applied whether the heating method is laser heating or induction heating. In the case of using laser heating as a heating method, (dT / dt) of the medium can be controlled by providing a light absorption layer whose light absorption rate and film thickness are adjusted.

The temperature dependence of Ku of the recording layer, and therefore R
Ku (T) can be controlled by appropriately selecting a material forming the recording layer. In the present invention, the coercive force Hc of the recording layer is preferably 4 kOe or more at room temperature so that recording can be performed on the recording layer containing fine magnetic particles by heating and recording can be maintained at room temperature.

In the case of a recording layer made of CoPt, which is a ferromagnetic substance, the Curie temperature decreases as the amount of Pt added increases, so that (dKu / dT) near room temperature can be increased. A similar effect can be obtained by increasing the amount of Cr added in the CoPtCr recording layer. Generally, (dKu / dT) near room temperature can be increased by increasing the amount of the nonmagnetic element added to the recording layer. On the other hand, when an additive element for increasing the Curie temperature is added to the recording layer, the opposite effect can be obtained.

In the case of a recording layer made of TbFeCo, which is a ferrimagnetic material used in a magneto-optical recording medium, the Curie temperature decreases as Co decreases, so that (dKu / dT) near room temperature should be increased. Can be. Further, if the recording layer is formed using a ferrimagnetic material having a Curie point higher than the maximum temperature of the recording layer by heating, the coercive force Hc can be maintained while RKu is maintained at a certain value.
Can be recorded. In this case, (T /
Since RKu) and T have a proportional relationship, there is an advantage that the design of the magnetic recording medium is facilitated.

The RKu of the recording layer can also be controlled by adjusting the size of the magnetic particles constituting the recording layer. As described above, CoCrP used for hard disks
The recording layer made of tTa or the like is composed of fine magnetic crystal grains separated so as not to cause exchange coupling interaction. If the recording layer is formed such that the volume of the magnetic crystal grains is reduced, the effect of thermal energy becomes relatively large, so that (dKu / dT) can be increased. This effect can be reduced by using a material having a large Ku. Thus, RKu of the recording layer can be controlled by selecting a material having an appropriate Ku. The Ku of the recording layer can be increased without changing the material by aligning the easy axis of the magnetization reversal in the plane of the recording layer from a random direction to one direction.

In order to satisfy the condition of the expression (1), the laser heating may be variously adjusted as shown below.

(1) The power of the laser to be irradiated is changed. The higher the irradiation power, the higher the maximum temperature of the recording layer.

(2) The method of laser irradiation is changed. For example, when the laser beam is continuously irradiated, heat flows in from a region where the laser beam has already passed. Therefore, the temperature change of the recording layer becomes gentle.

(3) Change the linear velocity of the recording medium with respect to the laser. Specifically, the rotation speed of the disk is changed. The higher the moving speed of the recording medium, the shorter the laser irradiation time on the area where the recording layer is located, so that the temperature rise is suppressed and the temperature change becomes steep.

(4) Pulse irradiation with a laser is performed to adjust the pulse width. The shorter the pulse width, the lower the temperature rise,
The temperature change becomes steep.

(5) In addition to the method of (4), the irradiation power is adjusted for each pulse. For example, a short pulse of low power is irradiated first for preheating, and then a high power pulse is irradiated for main heating. By this method, the temperature rise can be moderated. In this case, the combinations of the pulse widths, modulations, and powers of the pulse group can be considered almost infinite. Therefore, it is sufficient to select an optimal combination of pulse groups so as to satisfy the condition of Expression (1) for the recording layer exhibiting a certain RKu (T) characteristic.

(6) Change the shape of the laser beam. If the beam shape is long and oval along the moving direction of the medium, the temperature change of the recording layer can be moderated by the same effect as the effect described in (2). In this case, the shape of the laser beam may be changed by driving the laser optical system with a piezo element or a micromachine. By doing so, various RKu
(T) The beam shape can be adjusted according to the recording medium exhibiting the characteristics, the linear velocity of the medium, and the radius of rotation.

(7) Adjust the distance between the magnetic field applying means and the laser heating means. The farther the magnetic field applying means and the laser heating means are, the more gradual the temperature changes during recording. In this case, the position of the laser emission end may be driven by a piezo element or a micromachine. This makes it possible to adjust the above distance with respect to the recording medium exhibiting various RKu (T) characteristics, the linear velocity of the medium, and the radius of rotation.

The above methods (1) to (7) can be appropriately combined. Note that the same method as described above can be applied to a heating method other than laser heating.

Next, an example of recording on a magnetic recording medium having a recording layer made of an amorphous rare earth-transition metal alloy will be described. As a magnetic recording medium 10, on a 2.5-inch glass substrate 11, an underlayer 12 having a thickness of 110 n
m SiN, 20 nm thick GdTb as the recording layer 13
A layer in which FeCo and a protective layer 14 were formed by stacking SiN having a thickness of 40 nm and Au having a thickness of 25 nm was used.

The GdTbFeCo recording layer 13 is used for a magneto-optical recording medium, and is a ferrimagnetic material having perpendicular magnetic anisotropy. At room temperature, Ku is 10 ⁸ erg /
The cc and the coercive force Hc are as large as 8 kOe. Recording layer 1
The Ku of 3 decreases almost linearly as the temperature T approaches the Curie temperature. By adjusting the composition ratio of GdTb and FeCo, the coercive force Hc can be significantly reduced without significantly lowering Ku with a rise in temperature. This is a characteristic peculiar to the ferrimagnetic material.

This recording medium was rotated at a linear velocity of 8 m / s. Using a pickup for an optical disk, a laser beam having a wavelength of 650 nm was irradiated from the glass substrate 11 side. 0.7μm laser beam spot diameter on the medium
Focusing control was performed so that The recording operation was performed at a flying height of 100 nm by the recording / reproducing element 30 attached to the slider 10 as in FIG. While continuously irradiating a laser beam at 3 mW, the recording frequency was 200 kcfi.
Was used for magnetic recording. The recording track width was 2 μm. Reproduction was performed with a reproduction head having a GMR element.

When the recording layer 13 reaches the highest temperature,
RKu was 0.9, but the coercive force Hc was 8 k at room temperature.
It decreased from Oe to 0.9 kOe. If the coercive force has such a value, magnetic domains can be formed even with a normal recording head. When the time dependency of T / RKu in this experiment was estimated, it was found that the condition of Expression (1) was sufficiently satisfied because RKu was large.

However, when the GdTbFeCo recording layer was formed as an amorphous continuous film, a domain wall was always formed, and it was difficult to form fine magnetic domains.

Therefore, after forming a continuous film of GdTbFeCo, the continuous film was processed by electron beam lithography to form a structure in which cylindrical magnetic particles having a diameter of 10 nm were arranged at an interval of 10 nm from each other. The same recording experiment as described above was performed on this medium, and magnetic domains were observed by MFM. As a result, the existence of a domain wall was not recognized, and a recording magnetic domain was formed for each particle. This means that high-density recording in units of particle size is possible. As described above, it was found that a higher-density magnetic recording medium can be manufactured by processing the recording layer.

Next, an experiment was conducted to examine an appropriate time for applying a magnetic field after laser beam irradiation. In this experiment,
The magnetic recording medium having the CoPtCr recording layer described above was used.

(A) The structure of the recording medium, the laser power, and the number of revolutions of the disk were adjusted so that RKu ≧ 0.01 at the maximum temperature of the magnetic recording medium. Then, recording was performed while changing the time from when the recording medium reached the maximum temperature to when the recording was completed to 1, 2, 5, 10, 20, 50, and 100 ns. After the recording operation, it was examined whether or not a magnetic domain was formed by MFM. Except for 100 ns, it was found that magnetic domains were formed stably under all conditions. This is because the coercive force Hc of the recording layer increases as time elapses after reaching the maximum temperature,
It can be interpreted that stable recording cannot be performed. Further, in order to maintain the medium at a high temperature at which sufficient recording is possible for about 100 ns, the maximum temperature of the medium must be increased. Therefore, existing magnetic domains existing around the recording magnetic domain become unstable, and the magnetic domain becomes It may have been re-inverted.

(B) The structure of the recording medium, the laser power, and the number of revolutions of the disk were adjusted so that the maximum temperature of the magnetic recording medium exceeded the Curie temperature of the recording layer. in this case,
The recording medium reaches the Curie temperature before reaching the maximum temperature, the magnetization disappears, and RKu becomes zero. Then, recording was performed while changing the time from when the recording medium reached the maximum temperature to when the recording was completed to 1, 2, 5, 10, 20, 50, and 100 ns. After the recording operation, it was examined whether or not a magnetic domain was formed by MFM. Unlike the case (A), only when the time until the end of the recording is 20 ns or more,
It was found that magnetic domains were formed stably. This is RK
Since the recording magnetic domain is extremely unstable near u = 0, it can be interpreted that if the recording is completed early after reaching the maximum temperature, the magnetic domain will be re-inverted. Note that if a long time is required until the completion of recording as in this example, it is not preferable for improving the recording density and the transfer rate. However, in this example, a medium having a very large coercive force Hc at room temperature can be used, so that application to a low-speed magnetic recording system having extremely excellent recording retention characteristics can be considered.

[0068]

As described in detail above, according to the present invention, it is possible to provide a magnetic recording apparatus and a magnetic recording method capable of high-density recording exceeding the limit of thermal fluctuation.

[Brief description of the drawings]

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

FIG. 2: Ku, RKu, T / Ku and T / RKu;
The figure which shows the relationship of the temperature T.

FIG. 3 shows a logarithm 1 of an elapsed time t after recording on a magnetic recording medium.
FIG. 7 is a diagram showing a relationship between n (t) and the reciprocal 1 / T of the temperature T of the recording medium.

FIG. 4 shows RKu / T and l of a magnetic recording medium according to the present invention.
The figure which shows the relationship with n (t).

FIG. 5 is a diagram showing a relationship between T / RKu of a magnetic recording medium and an elapsed time t after recording according to the present invention.

FIG. 6 shows RKu / T and l of a magnetic recording medium according to the present invention.
The figure which shows the relationship with n (t).

FIG. 7 is a diagram showing a relationship between T / RKu of a magnetic recording medium and an elapsed time t after recording according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Magnetic recording medium 11 ... Substrate 12 ... Underlayer 13 ... Magnetic layer 14 ... Protective layer 20 ... Slider 30 ... Magnetic field applying means 40 ... Optical waveguide 41 ... Opening

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 5/02 G11B 5/64 G11B 11/10 502 G11B 11/105

Claims (9)

(57) [Claims] 1. A magnetic recording medium in which a recording layer composed of magnetic particles and a non-magnetic material interposed between magnetic particles is formed on a substrate, means for heating the recording layer, Means for applying a magnetic field, wherein the magnetic recording medium, the heating means, and the magnetic field applying means set a value of the magnetic anisotropy energy density of the recording layer at a temperature T of Ku (T) and a value at a room temperature Ta. Is Ku (Ta), and the ratio of these values is RKu
When (T) = Ku (T) / Ku (Ta), the ratio RKu (T) and the elapsed time t after the end of the application of the magnetic field are: T / RKu <11200 / (ln (t) +20.72) A magnetic recording device configured to satisfy the following relationship. 2. The recording layer having a coercive force of 4 k at room temperature.
2. The magnetic recording apparatus according to claim 1, wherein the magnetic recording apparatus is equal to or more than Oe. 3. The magnetic recording apparatus according to claim 1, wherein the recording layer is made of a Co-based alloy. 4. The magnetic recording apparatus according to claim 1, wherein said recording layer is made of a rare earth-transition metal alloy. 5. The magnetic recording apparatus according to claim 1, wherein said heating means and said magnetic field applying means are provided integrally. 6. A method for magnetic recording on a magnetic recording medium having a recording layer composed of magnetic particles and a non-magnetic material interposed between them on a substrate, wherein the recording layer is heated. And a step of recording by applying a magnetic field to the recording layer. The value of the magnetic anisotropy energy density of the recording layer at a temperature T is Ku (T), and the value at room temperature Ta is Ku (T). T
a), the ratio of these values is given by RKu (T) = Ku (T) / K
When u (Ta), the ratio RKu (T) and the elapsed time t after the end of the application of the magnetic field satisfy a relationship of T / RKu <11200 / (ln (t) +20.72). Magnetic recording method. 7. The coercive force of the recording layer is 4 k at room temperature.
7. The magnetic recording method according to claim 6, wherein the magnetic recording method is Oe or more. 8. In the heating step, heating is performed so that RKu (T _max ) at the maximum temperature T _max becomes 0.01 or less, and the recording operation is completed within 1 ns to 50 ns after the maximum temperature is reached in the recording step. 7. The magnetic recording method according to claim 6, wherein the recording is performed. 9. The method according to claim 9, wherein the RKu of the recording layer is used in the heating step.
(T) is heated so as to become 0 before the maximum temperature is reached, and in the recording step, 20 ns or more and 1 after the maximum temperature is reached.
7. The magnetic recording method according to claim 6, wherein the recording operation is completed within 00 ns.