JPH07296433A - Information recording / reproducing method, information recording / reproducing apparatus, and information recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] The areal recording density is improved by improving the reproduction resolution of the magnetic recording medium, and at the same time, the information is reproduced from each layer of the recording medium in which the recording layers are multi-layered and recorded in each layer. It is possible to increase the recording capacity of the recording medium. [Structure] Information is reproduced by irradiating an information recording medium with microwaves and recording information corresponding to the presence or absence of absorption of microwaves in a magnetic film. Information is reproduced by locally heating a part of the information recording medium irradiated with microwaves with an optical head. As the recording medium, one having a magnetic film of one layer or a plurality of layers formed on a transparent substrate is used.
The magnetic film is an amorphous alloy thin film whose main composition is one or more of heavy rare earth metals Tb, Dy and Gd, and Fe and Co. Further, information can be reproduced even on a magnetic film in which the recording layer is composed of a recording holding layer and a reproducing layer which are different from each other, and the recording holding layer and the reproducing layer are exchange-coupled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing method, an information recording device and an information recording medium using microwaves.

[0002]

2. Description of the Related Art With the advent of an information-oriented society, the amount of information we handle has increased dramatically. Among them, information recording / reproducing devices have become indispensable, and floppy disks and hard disks are widely used in computer peripheral devices and video tape recorders are widely used in AV-related fields. The recording density of these information recording apparatuses is remarkably improved, and the recording capacity is also increasing year by year. These magnetic recording media have a very low cost per bit as compared with semiconductor memories, and are suitable for applications requiring a large amount of information. However, in a multimedia environment that is expected to grow in the future, it is expected to handle enormous amounts of information including images and audio, and even hard disks and magneto-optical disks that have high recording density among magnetic recording, The recording capacity will be insufficient. Therefore,
Further densification and capacity increase of magnetic recording are being studied.

In a hard disk, a perpendicular magnetic recording method can be mentioned as a trump card for increasing the recording density. With such an increase in recording density, it is necessary to reduce the distance between the recording medium and the magnetic head. In the current hard disk drive, the flying height of the magnetic head is about 0.1 micron, and in order to dramatically reduce the flying height in the future, problems such as the surface condition of the recording medium and more precise control of the flying height of the magnetic head are overcome. This requires a great deal of effort to improve the recording density. Therefore, it is considered difficult to dramatically increase the recording capacity with the current low bit cost. Also, hard disks dislike dust and the like in order to realize the minute flying height. Therefore, there is a drawback that the recording medium cannot be replaced and the usage form is limited.

A method of compensating for the drawbacks of this high-density magnetic recording is an optical recording memory such as magneto-optical recording and phase change. A typical magneto-optical recording method will be described. Information is recorded by focusing light on the recording film, heating a region of about 1 micron square, and determining the direction of magnetization either up or down. Since the recording area is about the size of a light spot, the recording density is improved as compared with magnetic recording. The direction of magnetization is determined by the direction of external magnetization during heating, but since it can be recorded by a magnetic field of several hundred Oe, it is not necessary to place the magnetic field applying means close to the medium. Therefore, the recording medium is replaceable. In the magneto-optical recording method, a direct overwrite method by magnetic field modulation using a magnetic head has been proposed to improve the transfer rate, but in this case as well, the flying height of the magnetic head is much higher than that of high-density magnetic recording. The compatibility of the recording medium is ensured. The recording density of the optical recording method is limited by the beam spot diameter of the laser. The beam spot diameter is proportional to λ / NA (λ: laser wavelength, NA: numerical aperture of objective lens). Therefore, in order to improve the recording density, it is conceivable to shorten the laser wavelength or increase the NA of the objective lens. If the NA of the objective lens is increased, the control of the optical head is required to be more precise, which increases the load on the recording / reproducing apparatus. Therefore, the NA of the objective lens is set to about 0.65 as an upper limit, and the density is increased by shortening the wavelength of the light source. However, a semiconductor laser with a wavelength of 600 nm or less is currently in the research and development stage, and it will take a lot of time to put it into practical use. Further, when the wavelength is 300 nm or less, new problems such as absorption of light by the substrate occur, and thus there is a limit to increasing the optical recording density by only shortening the wavelength of the light source. As described above, even in the optical recording system, the densification of density is essentially limited.
It is considered that the density can be increased to about 10 times that of the magneto-optical recording device of m.

[0005]

In the magnetic recording system, it is known that it is possible to form a super high density magnetic domain by using a magnetic head. For example, according to "The 79th Research Society of Japan Applied Magnetics Society", P9, "Magnetic Media and Recording Magnetic Fields for Ultra-High Density Magnetic Recording", it is possible to form a magnetic domain of about 0.05 micron by the perpendicular magnetic recording method. It is possible. However, it is practically difficult to reproduce magnetic information recorded in such an ultra-high density because the SN ratio of the reproduction signal is lowered, and at present, only information having a size of about 0.2 μm can be reproduced. That is, the magnetic recording method has a problem that the resolution during reproduction is lower than the resolution during recording.

In the case of magneto-optical recording as well, it is known that it is possible to form a super high density magnetic domain using an optical head, as in magnetic recording. For example, according to "Optical Memory Symposium '90 Papers", P63, "Short Wavelength Recording Magneto-Optical Disk", it is easy to form a magnetic domain with a size of about 0.3 micron, and even a magnetic domain with a smaller size can be formed. It is possible. However, the beam spot diameter is considerably larger than that, and it is difficult to satisfactorily reproduce high-density recorded information by an ordinary reproducing method. That is, in the magnetic recording method including the magneto-optical recording, the resolution during reproduction is lower than the resolution during recording. Therefore, the recording density is limited by the reproduction resolution.

Further, in magnetic recording media, it is easy to think of an attempt to increase the recording capacity by forming multiple recording layers. It is relatively easy to record information on each layer of the magnetic film thus multilayered. However, it is very difficult to reproduce the information recorded in multiple layers. When a magnetic head is used, it is possible to easily reproduce information from the recording layer which is close to the magnetic head, but when the distance between the magnetic head and the recording layer increases, it becomes extremely difficult to reproduce the information. Not realistic. In the case of magneto-optical reading, if the recording layers are multi-layered, information can be reproduced from the first recording layer arranged on the light incident side. However, there is a problem that the reproduced signal from the second and subsequent recording layers cannot obtain a sufficient SN ratio,
At present, there is no reproducing method that can realize an increase in recording capacity due to multi-layering. In a magnetic recording method including magneto-optical recording, it is difficult to dramatically increase the recording capacity by increasing the number of recording layers.

As described above, the magnetic recording method including magneto-optical recording has a problem that the resolution during reproduction is low and the recording capacity cannot be increased by multilayering the recording layers.

[0009]

In the information recording / reproducing method of the present invention, the information recording medium is irradiated with microwaves to reproduce the information by absorbing the microwaves in the information recording medium. At the same time, a part of the information recording medium irradiated with microwaves is locally heated to reproduce information, and a laser beam is focused on the information recording medium by using an optical head, whereby A method of locally heating a part is desirable. Information is reproduced while applying a magnetic field to the information recording medium irradiated with microwaves. A method of reproducing information by irradiating microwaves having different frequencies or a method of reproducing information by changing the magnitude of the applied magnetic field may be used.

Further, the information recording / reproducing apparatus of the present invention has means for irradiating the information recording medium with microwaves of at least one kind of frequency, and means for detecting absorption of microwaves in the information recording medium. A Gunn diode or a klystron may be used as a means for irradiating the information recording medium with microwaves. An optical head is desirable as a means for locally heating a part of the information recording medium irradiated with microwaves. A means for applying a magnetic field to the information recording medium irradiated with microwaves to change the magnitude of the magnetic field is provided.

Further, in the information recording medium of the present invention, one layer or a plurality of layers of magnetic film are formed on the substrate. The magnetic film is
An amorphous alloy thin film having one or more selected from heavy rare earth metals Tb, Dy and Gd and Fe and Co as main compositions is desirable. Further, it is also preferable that the magnetic film is composed of a recording holding layer and an absorbing layer which are different from each other, and the recording holding layer and the absorbing layer are exchange-coupled. Garnet, ferrite or other oxides may be used for the magnetic film, and an in-plane magnetized film may be used as the magnetic film.

[0012]

The function of reproducing information using microwaves will be described. When the magnetic moment m is placed in the static magnetic field H,
Magnetic moments precess. The state of this precession exercise is shown in FIG. This precession diminishes with time and tends toward the static magnetic field (Fig. 2 (b)). Here, when a high frequency magnetic field h ₀ having the same frequency as that of the precession is applied in the direction perpendicular to the static magnetic field H, this precession continues without being attenuated. An electromagnetic wave has an electric field and a magnetic field vector in a direction perpendicular to its traveling direction, and their magnitude changes at the same frequency as the electromagnetic wave. Therefore, when a magnetic moment placed in a static magnetic field is irradiated with an electromagnetic wave of a certain frequency such that the static magnetic field and the magnetic field vector of the electromagnetic wave are perpendicular to each other, the magnetic moment continues to precess (Fig. 2 (a)). Energy is absorbed by the magnetic moment. This phenomenon is called magnetic resonance, and the frequency of the precession motion of the magnetic moment is called the resonance frequency. When a magnetic material such as a ferromagnetic material is placed in a static magnetic field, the same behavior will occur. That is, since the respective magnetic moments move uniformly by exchange coupling, the whole magnetic body performs a precession as one magnetization M. The resonance frequency of this precession is between 100MHz and 100GHz, which corresponds to the microwave frequency band. Therefore, when the magnetic material is irradiated with microwaves having a certain frequency, the microwaves are absorbed by the magnetic material.

Assuming that a thin film magnetic material is used as a sample and that the magnetic material exerts an anisotropic magnetic field H _A in a direction perpendicular to the film surface, the relationship between the microwave frequency and the applied magnetic field is expressed by the following equation. Be done.

When the static magnetic field H _r is in the sample plane:

[0015]

[Equation 1]

When the static magnetic field H _r is perpendicular to the sample:

[0017]

[Equation 2]

Where ω ₀ is the resonance frequency, M is the magnetization, and γ
Represents the gyromagnetic ratio. From these equations, it can be seen that the resonance frequency is different when the magnetic characteristics of the magnetic film are different.
In addition, when a certain magnetic field is applied and a microwave of a certain frequency is irradiated, the magnetic resonance state is different depending on whether the direction of the magnetization M and the direction of the static magnetic field H _r match. From this, it is understood that it is possible to reproduce the information by the microwave by making the magnetization direction correspond to whether the resonance condition is satisfied or not.

Next, the sensitivity of reproducing information by microwave will be described. The detection sensitivity of magnetic resonance is usually evaluated by the minimum spin number N _min , but the value is

[0020]

[Equation 3]

It is known that this is,
It is the detection sensitivity when the sample is placed in the cavity resonator.
Where V is the volume of the microwave cavity resonator and Q ₀ is its Q
The value, ΔH ₀ / H ₀ is the ratio of the resonance magnetic field H ₀ and the absorption line width ΔH ₀ , B is the bandwidth of the amplifier, and P ₀ is the microwave power. In a typical system, N _min will be on the order of 10 ⁹ -10 ¹⁰ . This value shows that the detection of magnetic resonance is very sensitive and is suitable for reproducing information recorded at high density.

As described above, reproduction of information by microwave has a very high detection sensitivity. However,
It is difficult to narrow down microwaves to less than 1 micron square. Therefore, when a disk-shaped or card-type recording medium is assumed, it is difficult to realize high surface resolution, that is, high surface recording density using only microwaves. Therefore, a high areal recording density was achieved by heating a part of the recording medium irradiated with the microwave. FIG. 3 shows the reproducing principle. A part of the recording medium is heated by irradiation with laser light (302) or the like. At this time, in order to cause magnetic resonance only when the temperature of the recording medium rises and the direction of the magnetization (308) of the recording film (307) is directed in a certain direction, the microwave (303) Frequency and applied magnetic field
Set the size of (309) in advance. In this case, the microwave is not absorbed in the region where the temperature has not risen because magnetic resonance does not occur. Since the absorption of microwaves occurs only in the heated region and when specific conditions are satisfied, it is possible to obtain a very high areal recording density.

Next, it will be shown that information from a plurality of stacked recording layers can be reproduced by using microwaves. The penetration depth (skin depth) of a good conductor of electromagnetic waves is

[0024]

[Equation 4]

It is expressed as Here, μ represents magnetic permeability, ω represents angular frequency, and σ represents conductivity. When a good conductor is irradiated with microwaves with a frequency of about 10 GHz, the penetration depth is about 1 μm. Therefore, when it is used as a recording layer of a magnetic layer having a thickness of 1000Å, it is possible to make a multilayer of about 10 layers. If the thickness of the magnetic layer is reduced, even if more magnetic films are laminated, The waves can penetrate well. Therefore, by changing the magnetic characteristics of each recording layer to change the resonance magnetic field and the resonance frequency, it is possible to reproduce the multiple-recorded information in the film thickness direction by using the microwave. Figure 4
Shows the principle of reproduction when the recording layers are multi-layered. FIG. 4 shows a case where the number of recording layers is two for the sake of simplicity. The recording medium is irradiated with two types of microwaves (403, 404) having different frequencies. The magnetic properties of the recording layer 1 (409) are set so that a part of the region whose temperature is raised by the laser (402) resonates by irradiation with the microwave (403) having the frequency ω ₁ . Recording layer 2 (4
In 10), the magnetic characteristics are set so as to resonate at the frequency ω ₂ . In both cases, the magnitude of the applied magnetic field during reproduction is set to be the same. By separately detecting the absorption of each microwave, the information recorded in the recording layer 1 and the recording layer 2 can be independently reproduced. As described above, by using the microwave, it is possible to independently reproduce the information from the multi-layered recording layers, so that the recording capacity can be increased several times as compared with the conventional recording / reproducing system. .
On the other hand, in the case of reproducing by light, the penetration depth becomes several hundred Å from the formula (4), and it is found that it is difficult to reproduce the information recorded in multiplex in the film thickness direction.

As described above, when the method of reproducing information using microwaves is compared with the method of reproducing light, the resolution in the surface direction is determined by the area of increased temperature, so that the surface recording density is the same or higher. Therefore, since it is possible to reproduce the information recorded in multiplex in the film thickness direction, the recording capacity of several times or more can be obtained by the reproduction by the microwave.

[0027]

EXAMPLES The present invention will be described below with reference to examples.

Embodiment 1 FIG. 1 is a block diagram of an apparatus used for reproducing information. A Gunn diode was used as the microwave oscillation source (105). Microwave frequency is 9.3GH
The power of z and microwave was set to 1 mW. A silicon crystal diode was used as the microwave detector (107), and the signal was detected by homodyne detection. The microwave oscillated by the Gunn diode is guided to the recording medium (101) by the waveguide (106), and the microwave partially absorbed by the recording medium reaches the detector through the recording medium. It is a configuration that is converted into an electrical signal. A disk-shaped recording medium is used, and is rotated at a constant angular velocity by a spindle motor (102). Optical head with laser wavelength of 830 nm (10
4) was placed directly above the recording medium, and the light spot was controlled so as to be focused on the recording layer of the recording medium. The spot diameter on the recording medium is about 1.4 microns. By forming a guide groove on the recording medium, the position of the light spot was controlled in the radial direction of the disk. As the recording medium, a transparent substrate having a recording layer formed thereon was used, and a laser beam was emitted from the substrate side and a microwave was emitted from the opposite side. The microwave detection system was arranged on the same side as the optical head with respect to the recording medium. As a means for applying a magnetic field to the recording medium during reproduction, a magnetic field applying coil (103) is arranged on the opposite side of the recording medium from the optical head, and a desired magnetic field can be obtained by passing a desired current. And

The recording medium used here was 750 Å AlSiN as a protective layer 1 and GdDyFeCo amorphous as a recording layer on a disk-shaped glass substrate having guide grooves formed by a photo polymer process (2P method). Alloy thin film 700 Å, further protective layer 2
As the AlSiN, 1000 Å was continuously deposited by the sputtering method. When the recording layer is irradiated with microwaves of 9.3 GHz, the resonance magnetic field is 3.5 kGauss at room temperature.
And was about 300 Gauss at 100 ° C. Also,
The easy axis of magnetization of the recording layer is perpendicular to the film surface, the Curie temperature is 180 ° C., and the coercive force at room temperature is 2.2 kOe.
Recording magnetic domains were previously formed on this recording medium by a magneto-optical recording method. Recording conditions are disk rotation speed 18
00 rpm, recording radius 30 mm, recording frequency 3.7 MHz, duty ratio 50%, recording magnetic field 300 Gauss. As a result, a recording magnetic domain having a domain length of 0.76 μm was formed in the recording layer.

A signal was reproduced from the recorded recording medium by microwave. Focused on the recording layer with a disk rotation speed of 1800 rpm and an optical head laser power of 2.5 mW,
A part of the recording layer was heated. 300G magnetic field in heated area
auss was applied. Here, the recording medium was irradiated with microwaves, and the signal of the absorption was measured with a spectrum analyzer. The evaluation conditions are a resolution bandwidth of 30 kHz and a video bandwidth of 100 Hz. The CN ratio of the measured reproduced signal at 3.7 MHz was 51.0 dB, and it was confirmed that good reproduction was possible. When the microwave was applied while applying the magnetic field without heating by the optical head, the 3.7 MHz component was not detected in the reproduced signal. From the above results, it was confirmed that it is possible to reproduce magnetic information only in the heated area by irradiating the microwave while heating a part of the recording medium. Further, when the same recording medium was measured by the magneto-optical reproducing method, the CN ratio was 50.3 dB. From the above, it was confirmed that the reproduction method using microwaves has almost the same reproduction characteristics as the magneto-optical reproduction method.

In the present embodiment, transmission type and homodyne detection is used for microwave detection. However,
There are various combinations of microwave detection methods. For example, there are reflection type detection and superheterodyne detection methods, and these methods are also effective. Further, a method of arranging the medium in the cavity to improve the detection sensitivity is also effective. As described above, the present invention is effective in various microwave detection methods and microwave circuits, and the present invention should not be considered to be limited to this embodiment.

Example 2 The information is reproduced by changing the microwave oscillation source (505) of the reproducing apparatus used in Example 1 to a klystron and the microwave detector (507) to a GaAs Schottky barrier diode. I did. The microwave frequency is 9.3 GHz. In addition, the microwave detector is a recording medium
It was arranged on the opposite side of the optical head (504) with respect to (501), and signals were detected by a reflection type arrangement. FIG. 5 is a block diagram of the reproducing apparatus used here. Magnetic field applying coil (503)
Was placed on the same side of the recording medium as the optical head. The recording medium used was 750Å of AlSiN as the protective layer 1, 400Å of TbFeCo amorphous alloy thin film and 300Å of GdFeCo amorphous alloy thin film as the recording layer on a disk-shaped glass substrate having guide grooves formed by the 2P method. Exchange-bonded laminated film of A, and A as the protective layer 2
lSiN was used by continuously depositing 1000 Å by sputtering method. Here, the TbFeCo film functions as a layer that retains recording, and GdFeCo functions as a layer that absorbs microwaves. When the GdFeCo layer as the absorption layer was irradiated with microwaves of 9.3 GHz, the resonance magnetic field was 3.5 kGauss at room temperature and about 300 Gauss at 100 ° C. On the other hand, since the TbFeCo layer of the recording holding layer used here does not have a resonance magnetic field near 300 Gauss in the range of room temperature to 130 ° C., it does not affect the reproduction. The TbFeCo layer has an easy axis of magnetization perpendicular to the film surface and a Curie temperature of 180.
℃. Furthermore, the coercive force of the exchange-coupled magnetic film at room temperature is 4.3 kOe. Information was recorded in advance on this recording medium under the same conditions as in Example 1.

Next, a signal was reproduced from the recorded recording medium by microwave. Disk speed 1800rp
m, the laser power of the optical head was 2.5 mW, and the light was focused on the recording layer to heat a part of the recording layer. Apply a magnetic field to the heated area
300 Gauss was applied. Here, the recording medium was irradiated with microwaves, and the signal of the absorption was measured with a spectrum analyzer. The evaluation conditions are a resolution bandwidth of 30 kHz and a video bandwidth of 100 Hz. 3.7 MHz of measured playback signal
The CN ratio was 49.8 dB, and it was confirmed that good reproduction was possible. When the microwave was applied while applying the magnetic field without heating by the optical head, the 3.7 MHz component was not detected in the reproduced signal.

From this example, it was confirmed that it is possible to use as the recording layer the exchange coupling film of the layer for holding the recording and the layer for absorbing the microwave. As a result, it is possible to use TbFeCo, DyFeCo, and other compositions of the magneto-optical recording material suitable for conventional high-density recording as they are as the recording holding layer, and to adjust the resonance condition of the absorbing layer without being influenced by the recording condition. Since it can be selected, any magnetic film satisfying the resonance condition can be used as the absorption layer.

Example 3 The reproduction of information from a recording medium having multiple recording layers will be described. FIG. 6 is a block diagram of an apparatus used for reproduction. Microwave source 1 (605) with a frequency of 9.3 GHz and microwave source 2 with a frequency of 15.0 GHz
Prepare (606). Both used Gunn diodes.
The microwave power was set to 1 mW. A silicon crystal diode was used as the microwave detector (609), and the signal was detected by homodyne detection.
This detector can detect microwaves of 9.3 GHz and 15.0 GHz with similar sensitivity. The microwave detection system was arranged on the same side as the optical head (604) with respect to the recording medium. The optical head for heating a part of the recording medium (601) is the same as that used in the first embodiment. A magnetic field applying coil (603) was arranged on the side opposite to the optical head with respect to the recording medium.

The structure of the recording medium used here is shown in FIG. Disk-shaped glass substrate with guide grooves formed by 2P method (7
On top of 01), 750Å AlSiN as the protective layer 1 (702), recording layer 1
(703) DyFeCo amorphous alloy thin film (704) 350Å and GdDyFeC
o Amorphous alloy thin film (705) 300Å exchange coupling laminated film, AlS as a dielectric layer (706) for separating recording layer 1 and recording layer 2
iN is 250Å, TbFeCo amorphous alloy thin film as recording layer 2 (707)
(708) 350Å and GdDyFeCo amorphous alloy thin film (709) 300Å exchange-coupling laminated film, and AlSiN 1000Å as protective layer 2 (710)
Was continuously formed into a film by a sputtering method. Here, the DyFeCo film of the recording layer 1 and the TbFeCo of the recording layer 2 are GdDyFe of the recording layer 1 and the recording layer 2 as layers for holding the recording.
Co functions as a layer that absorbs microwaves. When GdDyFeCo of the recording layer 1 was irradiated with a microwave of 9.3 GHz, the resonance magnetic field at room temperature was 3.9 kGauss, and at 120 ° C it was about 300 Gauss. 15.0GH for GdDyFeCo of recording layer 2
When irradiated with a microwave of z, the resonance magnetic field at room temperature was 3.0 kGauss and was about 300 Gauss at 80 ° C. On the other hand, the recording layer 1 used here, DyFeCo, and the recording layer 2
TbFeCo has no resonant magnetic field near 300 Gauss in the range of room temperature to 140 ° C, so it does not affect the reproduction. Further, in both DyFeCo of the recording layer 1 and TbFeCo of the recording layer 2, the easy axis of magnetization is perpendicular to the film surface, and the Curie temperatures of these films are 190 ° C. and 240 ° C., respectively. Recording was performed in advance on this recording medium. Recording conditions are a disk rotation speed of 1800 rpm and a recording radius of 30 mm. First, erasing was performed with a laser power of 11 mW, and recording was performed on the recording layer 2 under the conditions of a laser power of 10.5 mW, a recording magnetic field of 300 Oe, a recording frequency of 2.5 MHz, and a duty ratio of 25%. Subsequently, erasing was performed with a laser power of 5 mW, and recording was performed on the recording layer 1 under the conditions of a laser power of 6.5 mW, a recording magnetic field of 300 Oe, a recording frequency of 3.7 MHz, and a duty ratio of 20%.

Signals were reproduced by microwaves from the recording medium having the two recording layers recorded as described above. A part of the recording layer was heated by focusing on the recording layer with a disk rotation speed of 1800 rpm and a laser power of the optical head of 2.5 mW. A magnetic field of 300 Gauss was applied to the heated region. Here, the recording medium was irradiated with microwaves having a frequency of 9.3 GHz, and the absorption signal was measured by a spectrum analyzer. The reproduction signal was evaluated in the same manner as in Example 1. The measured reproduction signal has a CN ratio of 3.7 MHz of 5
It was 1.0 dB, and the signal of 2.5 MHz was not detected. Next, when the recording medium was irradiated with microwaves having a frequency of 15.0 GHz, the reproduced signal had a CN ratio of 2.5 MHz of 51.4 dB.
As before, the 3.7MHz signal was not detected. From the above, it was confirmed that in a recording medium having two recording layers, a good reproduction signal can be independently obtained even if signals of different frequencies are recorded in the respective recording layers. It was confirmed that the recording capacity can be dramatically increased because the recording films can be laminated.

In this embodiment, information is reproduced by irradiating microwaves of different frequencies separately. However, it is possible to reproduce information from a plurality of recording layers at the same time by irradiating the recording medium with microwaves having different frequencies at the same time and arranging a plurality of detectors for detecting the microwaves having only the respective frequencies. Further, although the recording medium having the two recording layers is used in the present embodiment, the present invention is effective even in the recording medium having three or more recording layers, and the present invention is limited to the present embodiment. Should not be considered.

Example 4 Another method of reproducing information from a recording medium having multiple recording layers will be described. The apparatus used for reproduction is the same as in Example 1, and the recording medium is irradiated with microwaves having a frequency of 9.3 GHz. The microwave detection system was arranged on the same side as the optical head with respect to the recording medium. The optical head for heating a part of the recording medium is the same as that used in the first embodiment.

Exchange coupling of 750Å AlSiN as the protective layer 1 and 350Å of the DyFeCo amorphous alloy thin film 350Å and the GdTbFeCo amorphous alloy thin film 300Å as the recording layer 1 on a disk-shaped glass substrate having guide grooves formed by the 2P method. Laminated film, AlSiN 250Å as a dielectric layer for separating recording layer 1 and recording layer 2, exchange-bonded laminated film of TbFeCo amorphous alloy thin film 350Å and GdTbFeCo amorphous alloy thin film 300Å as recording layer 2, and further protection AlS as layer 2
A recording medium was formed by continuously depositing 1000 N of iN by a sputtering method. Here, DyFe of recording layer 1
The Co film and the TbFeCo of the recording layer 2 function as a layer that retains recording, and the GdTbFeCo of the recording layer 1 and the recording layer 2 function as a layer that absorbs microwaves. When irradiated with 9.3 GHz microwave, GdTbFeCo in the recording layer 1 has a resonance magnetic field of 3.9 kGaus at room temperature.
s, and was about 300 Gauss at 120 ° C. GdTbFeCo of the recording layer 2 had a resonance magnetic field of 2.9 kGauss at room temperature and about 350 Gauss at 80 ° C. On the other hand, the DyFeCo of the recording layer 1 and the TbFeCo of the recording layer 2 used here are from room temperature.
Since it has no resonant magnetic field near 300 Gauss and 350 Gauss in the range of 140 ℃, it has no effect during reproduction. Further, in both DyFeCo of the recording layer 1 and TbFeCo of the recording layer 2, the easy axis of magnetization is perpendicular to the film surface, and the Curie temperatures of these films are 190 ° C. and 240 ° C., respectively. Recording was performed in advance on this recording medium. Recording conditions are a disk rotation speed of 1800 rpm and a recording radius of 30 mm. First, laser power 1
Erase at 1 mW, laser power 10.5 mW, recording magnetic field 3
Recording was performed on the recording layer 2 under the conditions of 00 Oe, recording frequency 2.5 MHz, and duty ratio 25%. Next, laser power
Erase at 5 mW, laser power 6.5 mW, recording magnetic field 30
Recording was performed on the recording layer 1 under the conditions of 0 Oe, recording frequency 3.7 MHz, and duty ratio 20%.

Signals were reproduced by microwaves from the recording medium having two recording layers recorded as described above. A part of the recording layer was heated by focusing on the recording layer with a disk rotation speed of 1800 rpm and a laser power of the optical head of 2.5 mW. A magnetic field of 300 Gauss was applied to the heated region. Here, the recording medium was irradiated with microwaves having a frequency of 9.3 GHz, and the absorption signal was measured with a spectrum analyzer. The reproduction signal was evaluated in the same manner as in Example 1. The measured CN ratio of the reproduced signal is 3.7MHz
It was 50.9 dB, and the signal of 2.5 MHz was not detected. Next, when the magnitude of the magnetic field applied to the recording medium was changed to 350 Gauss, the CN ratio of the reproduced signal at 2.5 MHz was 51.4 dB, and the 3.7 MHz signal was not detected.

As described above, in a recording medium having two recording layers, even if signals having different frequencies are recorded in the respective recording layers, a good reproduction signal can be independently obtained by changing the magnetic field applied during reproduction. It was confirmed that In the third embodiment, it has been described that the applied magnetic field at the time of reproduction can be the same and the reproduction can be performed by microwaves having different frequencies. However, in the present embodiment, the microwave of one certain frequency is irradiated. It was confirmed that information can be reproduced from the multi-layered recording film by changing the resonance magnetic field of the absorption layer. Needless to say, the present invention is not limited to these embodiments and is also effective for reproducing information by a microwave having a different frequency and a different magnetic field.

Example 5: The results of examining various materials for the microwave absorbing layer will be described. The apparatus used for reproduction is the same as that used in Example 2. The recording medium used was AlSiN as protective layer 1, 750 Å, TbDyFeCo amorphous alloy thin film 700 Å as recording holding layer, and 300 Å absorption layer on a disk-shaped glass substrate with guide grooves formed by the 2P method. As the layer 2, a layer of AlSiN continuously formed by 1000 Å by a sputtering method was used. Where TbDyFeCo
The membrane functions as a record-holding layer. Table 1 shows the composition of the four types of magnetic films examined as the absorption layer and whether the single layer is a perpendicular magnetization film or an in-plane magnetization film. Here, a perpendicular (in-plane) magnetization film is a magnetic field that is smaller when a magnetic field is applied in a direction perpendicular (in-plane) to the film surface than when a magnetic field is applied in an in-plane (perpendicular) direction. It is a film whose magnetization is saturated. Of the films having the compositions shown in Table 1, the oxide was formed in a mixed gas of argon and oxygen, and the films having other compositions were formed in argon gas. TbDy used here
The FeCo layer does not have a resonance magnetic field near 300 Gauss in the range of room temperature to 130 ° C., so that it has no influence during reproduction. The TbDyFeCo layer has an easy axis of magnetization perpendicular to the film surface and a Curie temperature of 190 ° C. As a result of measuring the magnetization of the recording films of the manufactured recording media, it was confirmed that the recording holding layer and the absorbing layer of the recording films of all the samples were exchange-coupled. Information was recorded on these recording media in advance under the same conditions as in Example 1. The recording frequency is 3.7MHz.

[0044]

[Table 1]

The signals from the recorded recording media were reproduced by microwaves. Disk speed 1800 rpm,
The absorption power was measured with a spectrum analyzer by irradiating each recording medium with microwaves while heating a part of the recording layer by focusing on the recording layer with a laser power of 2.3 mW of the optical head. The reproduction signal was evaluated in the same manner as in Example 1.

For sample 1, when the magnitude of the applied magnetic field during reproduction is 200 Gauss, the measured reproduction signal of 3.7 MHz
The CN ratio was 52.0 dB. Regarding sample 2, the CN ratio was 50.2 dB when the magnitude of the applied magnetic field was 250 Gauss. Regarding Sample 3, the CN ratio was 51.3 dB when the magnitude of the applied magnetic field was 350 Gauss. For sample 4,
CN ratio is 48.0 dB when the applied magnetic field is 180 Gauss
Met. From the above results, it is possible to use, as the absorbing layer, a heavy rare earth metal-transition metal alloy conventionally used for a magneto-optical recording material, and also a perpendicular magnetization film such as garnet, ferrite or other oxides. . Furthermore, it was confirmed that a reproduced signal with a high CN ratio can be obtained even by using an in-plane magnetized film such as Permalloy.

[0047]

As described above, by utilizing the absorption of microwaves in the recording layer, it becomes possible to detect the information recorded on the magnetic material with extremely high sensitivity. By heating a part of the region irradiated with the microwave, the reproduction resolution is improved and the recording density is increased. By heating the recording layer using an optical head, a recording density equal to or higher than the recording density of conventional optical recording can be achieved. By applying a magnetic field to the recording layer during reproduction, it is possible to reproduce information recorded at high density. Further, by changing the magnitude of the magnetic field applied during reproduction, it is possible to reproduce information from the recording layers having multiple layers and increase the recording capacity. Further, by forming the recording layer as an exchange coupling film composed of a recording holding layer and an absorbing layer, it is possible to use a conventionally used magnetic material for high density recording as the recording holding layer, and high density recording can be achieved. . At the same time, since the function of holding the record is not necessary for the absorption layer,
There is a merit that the range of choice is expanded. Further, by making the recording layers multi-layered and using microwaves of a plurality of frequencies, it is possible to increase the recording capacity of the medium and it is possible to reproduce information of different recording layers at once.

[Brief description of drawings]

FIG. 1 is a block diagram of an information reproducing apparatus of the present invention.

FIG. 2 is a diagram showing a change in motion of a magnetic moment due to absorption of microwaves.

FIG. 3 is a principle diagram of information reproduction of the present invention.

FIG. 4 is a principle diagram of information reproduction when a recording medium having multiple recording layers is used.

FIG. 5 is a block diagram of a reflective information reproducing apparatus of the present invention.

FIG. 6 is a block diagram of an information reproducing apparatus using microwaves of two frequencies according to the present invention.

FIG. 7 is a diagram showing a configuration of a recording medium used in Example 3.

[Explanation of symbols]

 101 Recording Medium 102 Spindle Motor 103 Magnetic Field Applying Coil 104 Optical Head 105 Microwave Oscillation Source 106 Waveguide 107 Microwave Detector 301 Objective Lens 302 Laser Light 303 Microwave 304 Heating Area 305 Resonance Area 306 Substrate 307 Recording Layer 308 Magnetization 309 Applied magnetic field 401 Objective lens 402 Laser light 403 Microwave 1 404 Microwave 2 405 Heating area 406 Resonance area 1 407 Resonance area 2 408 Substrate 409 Recording layer 1 410 Recording layer 2 411 Magnetization 412 Applied magnetic field 501 Recording medium 502 Spindle motor 503 Magnetic field applying coil 504 Optical head 505 Microwave oscillation source 506 Waveguide 507 Microwave detector 601 Recording medium 602 Spindle motor 603 Magnetic field applying coil 60 4 Optical head 605 Microwave oscillation source 1 606 Microwave oscillation source 2 607 Waveguide 1 608 Waveguide 2 609 Microwave detector 701 Substrate 702 Protective layer 1 703 Recording layer 1 704 Recording holding layer 1 705 Absorption layer 1 706 Dielectric layer 707 Recording layer 2 708 Recording holding layer 2 709 Absorption layer 2 710 Protective layer 2

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Claims (17)

[Claims] 1. An information recording / reproducing method, wherein information is reproduced by irradiating the information recording medium with microwaves and absorbing the microwaves in the information recording medium. 2. The information recording / reproducing method according to claim 1, wherein information is reproduced by locally heating a part of the information recording medium irradiated with microwaves. Method. 3. The information recording / reproducing method according to claim 2, wherein a part of the information recording medium is locally heated by focusing a laser beam on the information recording medium using an optical head. Characteristic information recording / reproducing method. 4. The information recording / reproducing method according to claim 1, wherein the information is reproduced while applying a magnetic field to the information recording medium irradiated with microwaves. 5. The information recording / reproducing method according to claim 1, wherein the information is reproduced by irradiating microwaves having different frequencies. 6. The information recording / reproducing method according to claim 4, wherein the information is reproduced by changing the magnitude of the applied magnetic field. 7. An information recording / reproducing apparatus comprising means for irradiating an information recording medium with microwaves having at least one or more kinds of frequencies, and means for detecting absorption of the microwaves in the information recording medium. 8. The information recording / reproducing apparatus according to claim 7, wherein a Gunn diode or a klystron is used as means for irradiating the information recording medium with microwaves. 9. The information recording / reproducing apparatus according to claim 7, further comprising means for locally heating a part of the information recording medium irradiated with microwaves. 10. The information recording / reproducing apparatus according to claim 9, wherein the means for locally heating a part of the information recording medium is an optical head. 11. The information recording / reproducing apparatus according to claim 7, further comprising means for applying a magnetic field to the information recording medium irradiated with microwaves. 12. The information recording / reproducing apparatus according to claim 11, further comprising means for changing the magnitude of the magnetic field. 13. An information recording medium for reproducing information by microwaves, characterized in that one layer or a plurality of layers of magnetic film are formed on a substrate. 14. The information recording medium according to claim 13, wherein the magnetic film has one or more selected from heavy rare earth metals Tb, Dy, and Gd, and an amorphous alloy mainly containing Fe and Co. An information recording medium characterized by being a thin film. 15. The information recording medium according to claim 13, wherein the magnetic film comprises a recording holding layer and an absorbing layer which are different from each other, and the recording holding layer and the absorbing layer are exchange-coupled with each other. recoding media. 16. The information recording medium according to claim 13, wherein the magnetic film is made of garnet, ferrite or other oxide. 17. The information recording medium according to claim 13, wherein at least one layer of the magnetic films is an in-plane magnetized film.