JP2000057649A - High-density magnetic recording and reproducing method and high-density magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to read out multiple-value information of an extremely large number by recording one kind of magnetization within multistage intensity proportional to the intensity of an impressed magnetic field in one spot of a magnetic recording medium, irradiating a recording section with linearly polarized light and reading out the rotating angle of the plane of polarization of light as the multiple-value information. SOLUTION: A reflection film 2, multilayered dielectric films, a magnetic film 3 which is a perpendicularly magnetized film and a protective film 4 are formed on a substrate 1. The magnetic field intensity by the soft magnetic core of the recording section is changed to six stages of ±0.5, ±0.75, ±1.0 k Gauss and the spot of 0.5 μm×05 μm is irradiated with a laser beam of 515 nm. Confirmation is then made that the rotating angle of the deflection plane of a Faraday effect is proportional to magnetic field intensity. As a result, confirmation is made that the rotating angle of the deflection plane may be read out as the multiple-value information. Since the rotation of the deflection plane of the Faraday effect is utilized, higher S/N may be obtd. The one side of the high-density magnetic recording layer is provided with a reflection layer and reproduction is executed by reflected light. Since the recording and reproducing head is arranged on one side, the device is made compact and the easy reproduction is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density magnetic recording / reproducing method and a high-density magnetic recording medium applicable to a large-capacity magnetic disk, a large-capacity magnetic tape, and the like.

[0002]

2. Description of the Related Art There are three typical types of conventional magnetic recording systems. One is an in-plane magnetic recording method, which is used for current audio, video, floppy, hard disk, and the like. A magnetic recording medium has in-plane magnetic anisotropy. If magnetized at an extremely short interval, the demagnetizing field increases, and leakage magnetic flux does not come out of the medium, and is not suitable for high-density recording. If the width of the recording unit is not as wide as 2 microns or more, the output is weak and the S / N is insufficient.

The second type is a perpendicular magnetic recording system, in which a magnetic recording medium has magnetic anisotropy in the direction perpendicular to the film surface, and can be magnetized even if one recording unit (bit) is about 50 nmφ.
Suitable for high density recording. However, if there is a space between the magnetic head and the medium, there is not much problem at the time of writing (because the head magnetic field is large), but at the time of reading (reproduction), it is necessary to detect a weak magnetic field from the medium. Since N has decreased, it has not been put to practical use.
In addition, if the reproduction is performed with strong contact with the medium surface in order to reduce the space between the magnetic head and the medium, wear of the medium and the head becomes a problem.

The third type is a magneto-optical recording system, which is used for a magneto-optical disk. In this method, a laser beam is absorbed by a magnetic recording medium, heated, magnetized by applying a weak magnetic field, and the polarization plane rotation angle of reflected light from the laser medium is reproduced as a binary digital signal.

As described above, the in-plane magnetic recording system is basically not suitable for high-density recording, and the perpendicular magnetic recording system is suitable for high-density recording. It is still a technology ahead. In the magneto-optical recording method, since thermomagnetic (heat mode) recording is performed, binary (with or without recording,
Or the direction of magnetization is plus or minus). That is, when a recording portion is heated, it is difficult to perform tens of multi-step intensity modulation recording even if the heating temperature or the magnetic field intensity is changed. Also, the Kerr rotation angle of the reflected light is used, but the angle is at most about 0.4 degrees at present, which is too small for multi-leveling. Therefore, when the signal changes at a high speed, it is impossible at present to resolve the signal into multiple values and detect it with the resolution of the detector.

[0006]

Therefore, recently, a multi-value recording method using a magneto-optical recording method of a multilayer film instead of recording on one recording layer has been studied. That is, the upper layer utilizes light transmission. For example, the 21st
Of the Annual Meeting of the Japan Society of Applied Magnetics (1997) 49
On page 9, as a future large-capacity image memory, a plurality of magnetic garnets having different wavelength characteristics of the Faraday effect are laminated to have wavelength selectivity, and wavelength multiplex reproduction (selective reading of signals of each layer) ( A laser having a wavelength corresponding to the number of magnetic layers is used) (NHK). Also, on page 501 of the Abstract of the Lecture (1997), the former uses magnetic garnet for both layers as a large-capacity memory, whereas the other uses magnetic garnet for one layer (using Faraday rotation of transmitted light). ), But the other uses a reflective magnetic film (using Kerr rotation of reflected light)
A multilevel magneto-optical recording method in which two laser wavelengths are selected from the wavelength characteristics of each layer is described (Nihon University). Further, the present inventor has disclosed in Japanese Patent Application No. 03-139788 (Japanese Unexamined Patent Application Publication No.
No. 3,386,611), ferromagnetic particles having different particle diameters are dispersed in the same layer, heated by laser light having a plurality of wavelengths according to the light absorption characteristics of the particle diameters, and Faraday rotation angles are individually read and reproduced. A method was proposed.

[0007] Of the above prior arts, those of NHK and Nihon University both have a multilayer structure. Moreover, since at least one layer uses Faraday rotation (light transmission), light absorption in this layer causes the light intensity to be practically insufficient when three or more layers are used, so that three or more layers are difficult. That is, there is a problem that the light intensity becomes insufficient due to the light absorption of the multilayer structure. Further, although a plurality of wavelengths selected according to the wavelength characteristics of each layer are used as the laser light, it is not practical to use a plurality of laser lights for each recording and reproduction. The most serious drawback is two layers ↓↓, ↓ ↑, ↑ ↓, ↑↑
Although it is difficult to form the four-valued and three-layers, it is limited to a small number of eight-valued as possible. That is, the maximum value is limited to eight values. Basically, as the number of multi-values increases, the light intensity becomes insufficient and the number of lasers increases, which makes practical use difficult. The proposal of Japanese Patent Application No. 03-139788 has the same problem.

The present invention has been made in view of the above background. Basically, only one kind of laser light is required, and there is only one magnetic layer. It is an object of the present invention to provide a multi-level recording medium and a recording method that can easily obtain numerical values, and that can have a plurality of magnetic layers and the same number of laser beams as the number of magnetic layers.

[0009]

According to the present invention, first, one kind of magnetization of a multi-step intensity proportional to the intensity of an applied magnetic field is recorded on one spot of a magnetic recording medium. There is provided a high-density magnetic recording / reproducing method characterized by irradiating a recording portion with linearly polarized light and reading out a polarization plane rotation angle of light as multi-valued information.

Secondly, there is provided a high-density magnetic recording / reproducing method according to the first aspect, wherein the rotation of the plane of polarization is caused by the Faraday effect.

Third, in the high-density magnetic recording / reproducing method according to the second aspect, a reflection film is provided on one surface of the magnetic recording medium, and reproduction is performed with reflected light. Is provided.

Fourth, there is provided a high-density magnetic recording / reproducing method according to the first aspect, wherein the rotation of the polarization plane is caused by the Kerr effect.

Fifthly, the magnetic recording medium used in the high-density magnetic recording / reproducing method described in the first, second, third or fourth aspect has at least one magnetic layer on a substrate, A high-density magnetic recording medium characterized by having magnetic anisotropy perpendicular to the substrate surface is provided.

Sixth, the magnetic recording medium used in the high-density magnetic recording / reproducing method described in the above first, second, third or fourth embodiment is composed of a plurality of recording layers having different wavelength dependencies of the Faraday effect. A high-density magnetic recording medium is provided.

Seventh, the magnetic recording medium used in the high-density magnetic recording / reproducing method described in the first, second, third or fourth aspect is characterized in that a ferromagnetic film is provided on a groove structure on a substrate surface. Provided is a high-density magnetic recording medium characterized by having a modified structure.

Eighth, a magnetic recording medium used in the high-density magnetic recording / reproducing method described in the first, second, third or fourth aspect has at least one magnetic layer on a substrate, A high-density magnetic recording medium is provided, wherein a dielectric multilayer film is provided on the magnetic layer, or the magnetic layer has a structure sandwiched by the dielectric multilayer films.

Hereinafter, the present invention will be described in detail. The present invention records one type of magnetization of multi-step intensity in proportion to the intensity of an applied magnetic field on one spot of a magnetic recording medium, and then irradiates the recording portion with linearly polarized light, thereby polarizing the transmitted light. The rotation angle is read as multi-value information corresponding to the multi-step magnetization intensity. Therefore, it is possible to record multiples according to the multi-valued number in one recording area than before, and the same recording medium,
For example, when a 5-inch diameter disk is used, recording can be performed several times in the same disk. 3 times for 8 values,
It is 4 times for 16 values and 5 times for 32 values. The following is a further explanation.

The magnetic recording medium of the present invention basically transmits or reflects light, particularly laser light in the visible region. This is because a large polarization plane rotation angle transmitted or reflected by the magnetic recording medium is used. Therefore, it is important that the rotation angle of the polarization plane of the magnetic recording medium after transmission or reflection is significantly different from the conventional one, and is several degrees (5 degrees or more, usually 10 degrees or more). In any case, conventional magnetic materials
As it is, it cannot be used in the present invention.

A feature of the present invention is that recording is performed by an intensity-modulated magnetic field, multi-step magnetic recording is performed with good reproducibility, and reproduction is performed by using a polarization plane corresponding to the multi-step magnetic recording intensity of linearly polarized light irradiated to the recording portion. There is a recording / reproducing method in which the rotation angle is read as multi-valued information. Basically, the recording / playback head is
It is good to be fixedly provided on one side of the recording medium, preferably on the recording layer side. This is because, if the recording and reproducing heads are separately arranged on the recording layer side and the substrate side of the recording medium, it becomes more difficult to adjust the position as the recording density increases. Therefore, in the present invention, when reading the Faraday rotation angle after passing through the recording medium, the reflective layer is provided and the recording is read from the side on which light is incident. This consideration is not particularly necessary when the car rotation angle is used.

The intensity of the applied magnetic field during recording is modulated by modulating the current of a coil used in a recording head.
For a ferromagnetic material to be used, if the magnetic field strength is such that the magnetic spin rotates all at once at a certain magnetic field strength or higher, it is always recorded at a constant magnetization strength, so multi-step magnetization is recorded. It is not possible. In a certain magnetic field strength range, it is necessary to be magnetized in proportion to the applied magnetic field strength. This magnetic field strength range is preferably 1 kGauss or less (depending on the material used) because the magnetic head can be made compact.

In the present invention, a so-called perpendicular magnetic recording medium having magnetic anisotropy perpendicular to the film surface is preferable as the magnetic recording medium because linearly polarized light is perpendicularly incident on the film surface for reproduction. This is because it is necessary for the magneto-optical properties that the traveling directions of the spin and the light are parallel. In this case, since the magnetic spin has an upward direction and a downward direction perpendicular to the film surface, the rotation angle of the polarization plane is reversed, and there is a merit unique to the present invention that a double multivalue can be obtained. This is an effect that cannot be obtained by the conventional magnetic recording method for detecting a change in magnetic flux described in the related art. It is needless to say that the conventional method in which the ferromagnetic film is heated and magnetized in a demagnetized state cannot be magnetized in multiple steps with good reproducibility.

In order to perform this multi-step magnetization on a small area of a perpendicular magnetic recording medium, a perpendicular magnetic head is preferable. This is because the magnetic field generated from the so-called magnetic head is preferably perpendicular to the film surface. The perpendicular magnetic head, which is the easiest to manufacture and can record at high density, has a rod-shaped soft magnetic material wound with a copper wire. The strength of the magnetic field is controlled by the value of the current flowing through the coil. However, if the distance between the surface of the ferromagnetic material and the tip of the perpendicular magnetic head is not constant, magnetization cannot be performed in multiple steps with good reproducibility.

The reason that the perpendicular magnetic recording method using such a perpendicular magnetic head has been difficult to put to practical use is that it is not easy to perform reproduction after recording with the perpendicular magnetic head. That is, perpendicular magnetic recording can be recorded as fine as about 100 mm in diameter, but can only be reproduced in about 500 mm in diameter due to the gap between the ferromagnetic material surface and the tip of the perpendicular magnetic head during reproduction. The fatal drawback is that only a larger area can be regenerated.

The present invention solves this problem by using perpendicular magnetic recording capable of high-density recording and reading out by a method using a polarization plane rotation angle of linearly polarized light that does not contact the magnetic recording medium during reproduction. It is for this reason that the recording and reproduction methods are different, and the good points of each method are used. In particular, in the case of the magnetic recording medium used in the present invention, the magneto-optical characteristics are greatly increased by the two methods as compared with the conventional method.

One is a method of forming a groove structure on a substrate surface. The polarization plane rotation angle of linearly polarized light greatly increases at a specific wavelength depending on the design value of the groove structure dimensions, so that the resolution and reproducibility of the magnetization intensity are greatly increased compared to the case of reproducing the magnetization directly with a magnetic head. It has the effect of doing. The present inventor has made detailed proposals on this point in several cases such as Japanese Patent Application No. 09-117626. That is, after forming a groove (having a rectangular, triangular or bowl-like shape) having a pitch and a depth of about the wavelength on the substrate surface, a transparent magnetic material thin film is provided on this surface. In order to further improve the transparency, the same function is obtained even if a part of the thin film between the grooves is removed. By changing the pitch and the depth as described above, an arbitrary visible light wavelength (several nm) can be obtained.
), The polarization plane rotation angle can be increased to 20 degrees or more. However, since the incident light is diffracted, zero-order diffracted light is used.

The other is a wavelength in which the ferromagnetic film is sandwiched between dielectric multilayer films and has a maximum magneto-optical characteristic (Faraday effect) according to the wavelength dependence peculiar to the ferromagnetic material. It can be designed to increase the rotation angle. In this regard, we have proposed in detail in Japanese Patent Application No. 09-154972 and several others. The dielectric multilayer film is formed by alternately stacking low-refractive-index layers and high-refractive-index layers. The film thickness is 1/4 of its optical thickness
λ (λ is the wavelength to be increased) is preferable,
There are other design methods. If the thickness of the magnetic layer is 1 / 2λ, light of λ can be transmitted, and magneto-optical characteristics can be increased. However, also in this case, there is a method of setting another film thickness. The magneto-optical characteristics can be arbitrarily increased by stacking the structure of the dielectric multilayer / magnetic layer / dielectric multilayer. As the magnetic layer, a transparent magnetic layer described later is used.

It is difficult to use the Faraday effect or the Kerr effect as a multi-level signal without changing the polarization plane rotation angle. When the two polarization function elements are rotated by θ degrees with respect to an axis (for example, an absorption axis in the case of an absorption type), the light intensity decreases in proportion to cos (θ). Therefore, in order to use it as a digital signal, the change in the rotation angle is first converted into an electric intensity signal through a polarizing element. Further, a method of converting into a digital signal using an AD converter is used.

An example of the effect of the present invention is as follows. When the rotation angle is +10 degrees (when the Faraday effect is used by reflection, it becomes +20 degrees due to the reciprocation of light in the medium).
20 degrees. Since the rotation angle detection resolution is at least 2 degrees or less, 20 values or more are possible (40 values in the case of Faraday). However, when the rotation angle is close to 0 degree and 90 degrees, the linearity is low, so that the value is slightly lower. A plurality of types of magnetic recording media having different wavelength dependencies of the Faraday effect are used in an overlapping manner. In this case, it is natural that the transparency of the layer near the surface is important, but the coercive force of each layer also needs to be different. In this case, for example, even if it has two layers, the storage capacity does not always become twice, but it is inevitable that the storage capacity becomes twice or less.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Materials used in the present invention are described below.
Embodiments will be described. First, used in the present invention
Transparent substrate, quartz glass, sapphire, crystallized
Transparent glass, Pyrex glass, Al₂O₃, Mg
O, BeO, ZrO₂, Y₂O₃, ThO ₂, CaO,
GGG (gadolinium, gallium, garnet), etc.
Inorganic transparent materials, MMA, PMMA, polycarbonate,
Polypropylene, acrylic resin, styrene resin, A
BS resin, polyarylate, polysulfone, polye
Tersulfone, epoxy resin, poly-4-methyl pen
Ten-1, fluorinated polyimide, fluororesin, phenoki
Transparent resin, polyolefin resin, nylon resin, etc.
A plastic film is used. Transparent plastic
Use of film has advantages such as lightness and flexibility.
Easy to use. When using a reflective film, the substrate is transparent
Any organic or inorganic material may be used.
You. However, if the surface is not smooth, magnetization can be reproduced in multiple steps
I can't record well.

As the reflection layer, A formed by the PVD method was used.
1, Cu, Ag, Au, Pt, Rh, Al ₂ O ₃ , Si
O ₂ , TeC, SeAs, TeAs, TiN, TaN,
CrN or the like is used.

As the polarizer layer, various commercially available polarizing films, high transmittance polarizers using a beam splitter, and the like can be used. The polarizing film is roughly classified into a polyhalogen polarizing film, a dye polarizing film, a metal polarizing film, and the like. More preferably, a Nicol prism, a Gran Thomson prism, a Gran Foucault prism, a Gran Taylor prism, a Lochon prism, a Wallaston prism and a combination thereof can be used as appropriate. In recent years, structural birefringent polarizers with artificially provided periodic fine structures on the order of wavelength, and reflective thin-film polarizers made by laminating thin films are applicable, but are not limited to these. It is not something to be done.

As the transparent magnetic layer, conventionally used generally
A transparent magnetic material exhibiting the magneto-optical effect
So-called performance with large Rad effect and high transparency
Magnetic materials with a large index are preferred. For example, 50 nm or less
Of ferromagnetic metals such as iron, cobalt and Ni
An ultrafine particle film is used. Other than ultrafine metal particles in this case
Is a film composition such as oxygen and carbon. Iron, Kovar
And Ni and other ferromagnetic metals show a large magneto-optical effect,
It cannot be used on a thin film as it is due to its high light absorption.
It has a large figure of merit when it is an ultrafine particle membrane
Become like Also, by controlling the particle size, an appropriate coercive force
Can be obtained. In addition, rare earth iron garnet and edge
Oxides, such as iron ferrite and Ba ferrite, FeBO
₃, FeF ₃, YFeO₃, NdFeO₃Birefringence
Is large, MnBi, MnCuBi, PtCo, etc.
There is. The above is mainly transparent and uses the Faraday effect
But then use reflection to make use of the Kerr effect.
For magnetic materials. What can be used in common
There is also. MnBi, MnCuBi, PtCo, GdC
o, GdFe, TbFe, GdTbFe, TbDyF
e, TbFeCo, DyFeCo, TbCo, etc.
You.

The greatest effect can be obtained when the traveling direction of light and the direction of spin are parallel to each other.
These materials are preferably films having magnetic anisotropy perpendicular to the film surface. For these transparent magnetic materials, general sputtering, vacuum deposition, PVD such as MBE, CVD, plating and the like are used.

Table 1 shows examples of materials used for the dielectric multilayer film.
3 are shown.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

Any of these materials may be appropriately selected, and other materials such as organic substances may be used. When a stack of dielectric materials having a low refractive index and a high refractive index is taken as one pair, the number of pairs is not limited, but 2 to 20 layers are preferable in terms of performance and cost. It is preferable that the two dielectric multilayer films in contact with the transparent magnetic material have exactly the same configuration. However, since the same type of film is used for the film directly in contact with the transparent magnetic material, the stacking order is reversed.

[0039]

The present invention will be described more specifically with reference to the following examples. Example 1 A 200 nm thick aluminum reflective film was provided on a 0.5 mm thick quartz substrate by vacuum evaporation. Then, using ion plating, SiO ₂
Is 89 nm (refractive index: 1.44), and Ta ₂ O ₅ is 61 nm.
(Refractive index: 2.1) Six layers were alternately laminated. The substrate temperature is 150 ° C. and the oxygen gas pressure is SiO ₂ .
1.0 × in the case of 1 × 10 ⁻⁴ torr and Ta ₂ O ₅
10 ^- was ⁴ torr. The film rate is SiO
₂ for 2 nm / sec, Ta ₂ O ₅ for 0.6 nm
/ Sec. The variation in the film thickness of the dielectric multilayer film was 3% of the total film thickness at the thickest portion and the thinnest portion. FIG. 1 shows the result of measuring the spectral transmittance of the dielectric multilayer film in the visible light region.

Next, a Bi-substituted rare earth iron garnet film was formed on the dielectric multilayer film by a sputtering method so as to have an average film thickness of 290 nm. Substrate temperature is 300 ℃
And Then, the film on the substrate was heated at 650 ° C. for 3 hours in air.
Heated for hours. The composition of the film is Bi _2.2 Dy _0.8 Fe
_3.8 Al _1.2 O ₁₂ FIG. 2 shows the wavelength dependence (applied magnetic field of 10 K gauss) of the Faraday rotation angle measured by a magneto-optical effect measuring device (K250 manufactured by JASCO Corporation). At a wavelength of 515 nm, the value of the rotation angle was 0.9 degrees. The hysteresis of the Faraday rotation angle at a wavelength of 515 nm measured by the apparatus is as shown in FIG. 3, and it can be seen that the film is a so-called perpendicular magnetization film having a strong anisotropic magnetic field perpendicular to the film surface. The coercive force measured by applying a magnetic field perpendicular to the film surface with the VSM was 600 Oe.

Next, a multilayer film of SiO ₂ and Ta ₂ O ₅ was formed on the Bi-substituted rare earth iron garnet film by ion plating in exactly the same order as described above. Wavelength dependence of Faraday rotation angle (Fig. 4, applied magnetic field 1
0K Gauss), the rotation angle was 11 degrees at a wavelength of 515 nm.

As shown in FIG. 5, recording was performed on the magnetic layer from the magnetic layer side of the above-mentioned film composition using the recording portion of the recording / reproducing head. Recording was performed by changing the magnetic field intensity by the soft magnetic core of the recording portion in three steps so as to be 0.5, 0.75, and 1.0 K Gauss in the magnetic layer. L in FIG. 5 in this case
(Distance between recording / reproducing head and protective film) was about 50 nm. The size of the recorded spot was 0.5 × 0.5 μm. In another magnetic recording layer produced in the same manner, ± 0.
In the case where recording is performed in six steps so as to be 5, ± 0.75, ± 1.0K Gauss, the Faraday rotation angle (zero magnetic field) measured by the magneto-optical effect measuring device is linear as shown in FIG. Has increased. The magnetic recording spot was irradiated with a laser beam of 515 nm, and the Faraday rotation angle was measured. There was a proportional relationship corresponding to ± 0.5, ± 0.75, ± 1.0K Gauss. Thus, 1 of the magnetic recording medium
Recording one type of magnetization of multi-step intensity in proportion to the intensity of the applied magnetic field on a spot, irradiating the recording part with linearly polarized light, and reading the polarization plane rotation angle of light as multi-valued information Was completed.

Example 2 An iron film having a thickness of 200 nm was formed on a quartz substrate by vacuum evaporation. Next, Example 1
A dielectric multilayer film of SiO ₂ and Ta ₂ O ₅ was produced in exactly the same manner as described above. From the wavelength dependence of the Kerr rotation angle for measuring the polarization plane rotation angle of the reflected light, the rotation angle was 10 degrees at a wavelength of 515 nm. Hysteresis and VSM of Kerr rotation angle at a wavelength of 515 nm measured with the same device as in Example 1.
From the measurement results, having a strong anisotropic magnetic field perpendicular to the film surface,
It turned out to be a so-called perpendicular magnetization film. Recording was performed on the magnetic layer from the magnetic layer side of the above-described film composition using the recording section of the recording / reproducing head in the same manner as in Example 1. 515 nm
Was irradiated on the magnetic recording spot, and the Kerr rotation angle was measured. There was a proportional relationship corresponding to ± 0.5, ± 0.75, ± 1.0K Gauss.

[Embodiment 3] The reflection layer, dielectric multilayer film and magnetic layer (Bi _2.2 Dy _0.8 Fe _3.8 Al) of the first embodiment were used.
_In addition to the laminated recording layer with _1.2 O ₁₂ ), another laminated recording layer was formed thereon. SiO ₂ has a thickness of 110
nm and Ta ₂ O ₅ were 76 nm, and six layers were alternately laminated. The magnetic layer was formed using the sputtering method as in the first embodiment.
It was produced with a film thickness of 150 nm. The composition is Bi _0.4 Dy
_2.8 Ge _0.4 Co _0.4 Fe _{4. 1} O ₁₂ . The magnetic layer (Bi _0.4 Dy _2.8 Ge)
_0.4 Co _0.4 Fe _4.1 O ₁₂ ), the wavelength dependence of the Faraday rotation angle is 633 n
m had a rotation angle peak of 12 degrees in the minus direction. From the hysteresis of the Faraday rotation angle at a wavelength of 635 nm, it was found that the film was a perpendicular magnetization film having magnetic anisotropy in a direction perpendicular to the film surface, and the coercive force was 2 KOe.

From the magnetic layer side of the above-mentioned film composition, Example 1
In the same manner as described above, recording was performed on the magnetic layer using the recording section of the recording / reproducing head. Recording was performed by changing the magnetic field strength by the soft magnetic core of the recording portion in six steps so as to be ± 0.5, ± 0.75, ± 1.0 K Gauss in the magnetic layer. When the laser beam wavelength of the reproducing head is set to 515 nm, the magnetic layer (B
_i2.2 Dy _0.8 Fe _3.8 Al _1.2 O ₁₂ ) was irradiated on the spot to measure the Faraday rotation angle. ±
There was a proportional relationship corresponding to 0.5, ± 0.75, ± 1.0K Gauss.

Next, in the same manner as in Example 1, the current value of the recording / reproducing head was increased, and recording was performed on the magnetic layer. The magnetic field strength of the soft magnetic core of the recording part
Recording was performed in six steps so as to be 2.5, ± 3.0, ± 3.5K Gauss. When the laser beam wavelength of the reproducing head is 633 nm, the magnetic layer (Bi _0.4 Dy _2
. By irradiating _{8 Ge 0.4 Co 0.4 Fe 4.1 O} 12) of the spot was measured Faraday rotation angle. ± 2.
There was a proportional relationship corresponding to 5, ± 3.0, ± 3.5K Gauss.

From these results, it was found that in a plurality of recording layers having different wavelength dependencies of the Faraday effect, one spot (as viewed from the upper surface of the magnetic recording medium) of a multi-step intensity in proportion to the intensity of the applied magnetic field was formed at one spot. When one type of magnetization was recorded, the recording site was irradiated with linearly polarized light, and the polarization plane rotation angle of the light was read out as multi-valued information, it was found that a higher recording density was obtained than in the case of a single layer. .

Example 4 One layer of a 1 mm thick quartz substrate was provided with two layers of Cr ₂ O ₃ and then Cr so as to have a total thickness of 120 nm. Further, a positive resist was provided thereon. A photomask is placed on this resist, and U
Exposure was performed using V light so that L = 1.0 μm in FIG. Next, the resist layer was etched using a wet etching technique, and the quartz surface was further etched using a fluorine-based gas, whereby processing was performed so that H = 0.65 μm. Next, the resist layer was peeled off.

An iron fine particle film was deposited on the processed surface of the quartz substrate by using a gas deposition method without heating the substrate.
The used Ar gas was flowed at a flow rate of 50 CCM, and the total pressure was set to 1.0 Pa. The average film thickness was 100 nm. The average particle diameter of the iron fine particles measured by a transmission electron microscope is 6 nm.
Met. The composition of the film was 66% iron and the others were oxygen, carbon and nitrogen. The coercive force of the iron fine particle film measured at the flat portion was 320 Oe, the squareness ratio in the in-plane direction was 0.80, and the film had in-plane magnetic anisotropy.

The wavelength dependence (the vertical axis is the polarization plane rotation angle deg) of the magneto-optical element manufactured as described above is measured with a magneto-optical effect measuring apparatus (the polarization plane of the incident light is perpendicular to the grating groove direction). And a peak appeared at 633 nm. The hysteresis of the polarization plane rotation angle of the transmitted light with respect to the applied magnetic field was measured at a wavelength of 633.7 nm and a maximum applied magnetic field of 10 K Gauss (FIG. 8).

Using the recording section of the recording / reproducing head, recording was performed on the magnetic layer on the magnetic layer side of the above film composition in the same manner as in Example 1. Recording was performed by changing the magnetic field strength by the soft magnetic core of the recording portion in six steps so as to be ± 0.5, ± 0.75, ± 1.0 K Gauss in the magnetic layer. With the laser beam wavelength of the reproducing head set to 633 nm, the magnetic recording spot was irradiated and the polarization plane rotation angle of the transmitted light was measured.
Corresponding to ± 0.5, ± 0.75, ± 1.0K Gauss,
There was a proportional relationship.

Comparative Example 1 A recording medium was prepared on a disk-shaped quartz substrate in the same manner as in Example 1, and magnetic recording was performed from the magnetic layer side using a recording coil portion of a recording / reproducing head. As in Example 1, +0.5 perpendicular to the film surface,
Three types of magnetic fields of +0.75 and + 1.0K Gauss were applied. Next, using the coil portion of the head used for the same recording, reproduction was attempted to read the output due to the change in magnetic flux when the recording medium was moved. The output by the recording part was confirmed. However, because of the small magnetized area, the output was not proportional to the three types of applied magnetic field strength. Next, three magnetic fields of -0.5, -0.75, and -1.0 K Gauss perpendicular to the film surface were applied. The output in this case is +0.
5, +0.75, almost the same as + 1.0K Gauss. That is, despite recording in six values, it was not possible to read as multi-valued information in six different stages.

Comparative Example 2 A recording medium was produced in the same manner as in Example 1 except that the reflective film was not provided. The magnetic recording was performed in the same manner as in the example, but another light receiving head was required on the opposite side of the substrate for reproduction in addition to the recording head of the example 1. In reproducing, it was very difficult to match the recording position with the reproducing head position.

Comparative Example 3 A recording medium was manufactured in exactly the same manner as in Example 2. Next, the recording medium is irradiated with a laser beam of 515 nm by using the optical reproducing section of the recording / reproducing head and heated, and from the back side of the quartz substrate where the magnetic layer is not provided, ± 0.5, ± 0.75 perpendicular to the film surface. , ± 1.0 K Gaussian, and recorded on the magnetic layer. The Kerr rotation angle of the reflected light was measured using the recording / reproducing head. Despite the difference in magnetic field strength during recording, the rotation angle is the same,
Multi-valued information could not be obtained.

Comparative Example 4 In Example 1, the heating temperature in air after forming the Bi-substituted rare earth iron garnet film was changed to 6
A recording medium was produced in exactly the same manner except that the temperature was lowered to 20 ° C. At a wavelength of 515 nm, the peak value of the rotation angle was 0.9 degree. In the hysteresis of the magnetic characteristics measured by the VSM, the anisotropic magnetic field in the direction perpendicular to the film surface was slightly reduced from the case of heating at 650 ° C. in Example 1 and was close to isotropic. The coercive force measured by applying a magnetic field perpendicular to the film surface with the VSM was 360 Oe. Next, a multilayer film of SiO ₂ and Ta ₂ O ₅ was produced in exactly the same order as in Example 1. From the wavelength dependence of the Faraday rotation angle, a wavelength of 5
At 15 nm, the rotation angle was 10 degrees. Recording was performed from the side of the magnetic layer of the above film composition. The magnetic field strength by the soft magnetic core of the recording portion is ± 0.5, ± 0.75, ±
Recording was performed in six steps so as to be 1.0 K Gauss. The magnetic recording spot was irradiated with a laser beam of 515 nm, and the Faraday rotation angle was measured. ± 0.5,
Corresponding to ± 0.75 and ± 1.0K Gauss, a proportional relationship could be confirmed, but the variation of the rotation angle became large.

Comparative Example 5 A magnetic recording medium having a single recording layer described in Example 3 is referred to as Comparative Example 5.

Comparative Example 6 An iron fine particle film was prepared in exactly the same manner as in Example 2 except that no groove structure was formed on the quartz substrate. The average film thickness, average particle diameter, film composition, coercive force, and squareness ratio in the in-plane direction were the same as in Example 1. In the wavelength dependence of the rotation angle measured by the magneto-optical effect measurement device,
The value showed a substantially constant value of 0.1 degree regardless of the wavelength. Recording was performed on the magnetic layer using the recording section of the recording / reproducing head in the same manner as in Example 1. The magnetic field strength by the soft magnetic core of the recording portion is ± 0.5, ± 0.75, ±
Recording was performed in six steps so as to be 1.0 K Gauss. Assuming that the laser beam wavelength of the reproducing head is 633 nm,
The Faraday rotation angle was measured by irradiating the magnetic recording spot. Despite changing the applied magnetic field strength, such as 0.5, ± 0.75, ± 1.0K Gauss, the Faraday rotation angle did not change correspondingly.
Less than 1 degree, no proportional relationship could be found.

[Comparative Example 7] On a quartz substrate having a thickness of 5 mm,
A Bi-substituted rare-earth iron garnet film was manufactured to have an average film thickness of 290 nm exactly in the same manner as in Example 1 except that the dielectric multilayer film of iO ₂ and Ta ₂ O ₅ was not provided. In Example 1, as shown in the evaluation results of the Bi-substituted rare earth iron garnet film on the dielectric multilayer film, the rotation angle peak at a wavelength of 515 nm was obtained from the wavelength dependence of the Faraday rotation angle measured by the magneto-optical effect measurement device. The value was 0.9 degrees. Similarly, from the hysteresis of the Faraday rotation angle at a wavelength of 515 nm, it was found that the film was a so-called perpendicular magnetization film having a strong anisotropic magnetic field perpendicular to the film surface.
The coercive force measured by applying a magnetic field perpendicular to the film surface with the VSM was also 600 Oe. Recording was performed on the magnetic layer in the same manner as in Example 1 from the magnetic layer side. The magnetic field strength by the soft magnetic core of the recording section is ± 0.5, ± 0.75,
Recording was performed in six steps so as to be ± 1.0 K Gauss. The magnetic recording spot was irradiated with a laser beam of 515 nm, and the Faraday rotation angle of the reflected light was measured.
Despite changing the applied magnetic field strength such as ± 0.5, ± 0.75, ± 1.0K Gauss, the Faraday rotation angle did not change correspondingly, and all were 0.9 degrees or less. It was small and no proportional relationship could be found.

[0059]

As described above, according to the high-density magnetic recording / reproducing method of the first aspect, the magnetization proportional to the intensity of the applied magnetic field is recorded on one spot of the magnetic recording medium, and the recording portion is irradiated with linearly polarized light. Since the rotation angle of the polarization plane of light is read out, multi-value recording can be performed on the same spot, and a high-density, large-capacity memory can be manufactured.

In the high-density magnetic recording / reproducing method according to the second aspect, since the rotation of the polarization plane caused by the Faraday effect is used in the method according to the first aspect, it can be easily converted into the light intensity, and the S / N ratio can be improved. High multi-value recording is now possible.

According to a third aspect of the present invention, in the method of the second aspect, a reflection film is provided on one surface of the recording layer of the high-density magnetic recording medium.
Since the recording / reproducing head can be arranged on one side, the apparatus becomes compact and the recording / reproducing means such as tracking can be simplified.

In the high-density magnetic recording / reproducing method according to the fourth aspect, since the rotation of the polarization plane due to the Kerr effect is used in the first aspect, it is possible to perform one-sided recording / reproduction without providing a reflective film. Since only one side of the multilayer film is required, the recording medium can have a simple configuration, and the performance can be improved, such as easy tracking.

A high-density magnetic recording medium according to a fifth aspect is a magnetic recording medium used in the high-density magnetic recording / reproducing method according to the first, second, third or fourth aspect, having a structure having magnetic anisotropy perpendicular to the substrate surface. As a result, the interaction with light at the time of optical reproduction is strengthened, so that larger multi-valued recording can be performed.

The high-density magnetic recording medium according to claim 6 is a magnetic recording medium used in the high-density magnetic recording / reproducing method according to claim 1, comprising a plurality of recording layers having different wavelength dependences of the Faraday effect. With such a configuration, it is possible to perform multiplex recording on a plurality of recording layers, and it is possible to perform higher-density recording.

A high-density magnetic recording medium according to a seventh aspect is a magnetic recording medium used in the high-density magnetic recording / reproducing method according to the first, second, third or fourth aspect, wherein a ferromagnetic film is provided on the groove structure on the substrate surface. With the configuration, a large magneto-optical effect is obtained,
Large multi-value recording can be performed.

The high-density magnetic recording medium according to the eighth aspect is a magnetic recording medium used in the high-density magnetic recording / reproducing method according to the first, second, third or fourth aspect, wherein a dielectric multilayer film is provided on the magnetic recording layer, Since the magnetic recording layer has a structure sandwiched by the dielectric multilayer films, the magneto-optical effect at a specific wavelength can be increased, and large multi-value recording can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing the spectral transmittance of a dielectric multilayer film in Example 1.

FIG. 2 is a diagram showing the wavelength dependence (I) of a Faraday rotation angle measured in Example 1.

FIG. 3 is a diagram showing a hysteresis of a Faraday rotation angle measured in Example 1.

FIG. 4 is a diagram showing the wavelength dependence (II) of the Faraday rotation angle measured in Example 1.

FIG. 5 is a diagram showing a recording / reproducing head.

FIG. 6 is a diagram showing a relationship between an applied magnetic field measured in Example 1 and a Faraday rotation angle.

FIG. 7 is a cross-sectional view schematically showing a groove structure on a substrate.

FIG. 8 is a diagram showing magneto-optical characteristics of a high-density magnetic recording medium manufactured in Example 4.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Reflective film 3 Magnetic film 4 Protective film 10 Recording / reproducing head 11 Objective lens 12 Coil 13 Soft magnetic coil 20 Light L L in FIG. 5 shows the distance between the recording / reproducing head and the protective film 100 Transparent substrate 110 Iron super Fine particle film L L in FIG. 7 indicates the exposure width of the UV light at the time of forming the groove structure.

Claims (8)

[Claims] 1. A magnetic recording medium in which one type of magnetization of a multi-step intensity proportional to the intensity of an applied magnetic field is recorded on one spot of a magnetic recording medium, and the recording portion is irradiated with linearly polarized light, thereby obtaining a polarization plane of light. A high-density magnetic recording / reproducing method characterized by reading a rotation angle as multi-valued information. 2. The high-density magnetic recording / reproducing method according to claim 1, wherein the rotation of the plane of polarization is based on the Faraday effect. 3. The high-density magnetic recording / reproducing method according to claim 2, wherein a reflection film is provided on one surface of the magnetic recording medium, and reproduction is performed with reflected light. 4. The high-density magnetic recording / reproducing method according to claim 1, wherein the rotation of the polarization plane is based on the Kerr effect. 5. A high-density magnetic recording medium according to claim 1, wherein said magnetic recording medium has a magnetic anisotropy perpendicular to a substrate surface. recoding media. 6. A magnetic recording medium used in the high-density magnetic recording / reproducing method according to claim 1, comprising a plurality of recording layers having different wavelength dependencies of the Faraday effect. High density magnetic recording medium. 7. A magnetic recording medium used in the high-density magnetic recording / reproducing method according to claim 1, having a structure in which a ferromagnetic film is provided on a groove structure on a substrate surface. High density magnetic recording medium. 8. A magnetic recording medium used in the high-density magnetic recording / reproducing method according to claim 1, wherein the magnetic recording medium has at least one magnetic layer on a substrate, and has a dielectric layer on the magnetic layer. A high-density magnetic recording medium comprising: a multi-layered magnetic film; or a structure in which the magnetic layer is sandwiched between dielectric multi-layered films.