JPH07334875A - Information recording / reproducing method and information recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] Information is reproduced from a reproduction-only information recording medium in which recording pits are formed with high density. In an information recording / reproducing method of locally heating an information recording medium and simultaneously irradiating the information recording medium with microwaves to reproduce the information using absorption of the microwaves in the information recording medium, Correspondingly, information is reproduced by using the change in the absorption of microwaves in the uneven portion formed in advance on the information recording medium. When reproducing information, a laser beam is focused on the information recording medium using an optical head to locally heat a part of the information recording medium. The information recording medium used there is composed of a substrate on which irregularities corresponding to the information to be recorded are previously formed, and a magnetic film. Further, the unevenness and the magnetic film corresponding to another recording information are formed at least once on the recording medium in which the magnetic film is formed on the substrate on which the unevenness corresponding to the recording information is formed.

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 for reproducing information using absorption of microwaves and an information recording medium used therefor.

[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 peripherals, and video tape recorders are widely used in AV-related fields. All of these information recording devices are rewritable recording media. On the other hand, the reproduction-only information recording medium includes a CD-ROM, a laser disk, and the like.

In recent years, these read-only media have rapidly spread, and the reason is that the recording capacity is very large and the media cost is low. For example, in the case of a CD-ROM, the recording capacity exceeds 500 MByte. Further, its structure is very simple, and unevenness called a recording pit is formed by injection molding on a resin substrate such as polycarbonate, and a reflective film is formed thereon. Since a large number of copies can be made from a mold called a stamper, a read-only medium using the unevenness of the substrate can be manufactured at a very low cost. On the other hand, in the case of a magneto-optical disk that is a rewritable medium, at least four thin films must be formed on a similar substrate. Further, in magneto-optical reproduction, in order to detect a minute change in the Kerr rotation angle in the recording domain, the substrate and its unevenness must be controlled more precisely. On the other hand, the CD-ROM is a method of detecting the change in the reflectance at the recording pit, and the change is sufficiently larger than the change in the Kerr rotation angle, and the margin for manufacturing the CD-ROM is wide. As described above, the read-only medium has been widely used because it has a wide manufacturing margin and is inexpensive.

Further, even in a multimedia environment which is expected to develop in the future, the read-only medium is considered to be very important. In a multimedia environment, information such as images, sounds and texts is digitized and processed. In this case, since the amount of information such as images and sounds is enormous, it is required to increase the recording capacity of the device and the medium for processing and recording them. As the amount of information handled in this way increases, the amount of information inevitably increases in distribution, commercially available software, video, and the like. There is a need for a read-only medium that is inexpensive and can be copied in large quantities.

[0005]

The reproduction resolution of a read-only medium such as a CD-ROM by optical reading 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. In addition, the thickness of the substrate and the warp of the substrate are severely restricted, which increases the cost of the medium. Therefore, the NA of the objective lens is set to about 0.65 as the upper limit, and the resolution of reading is improved 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 improving the reading resolution by only shortening the wavelength of the light source. For this reason, it is considered that it is only possible to achieve a high resolution of reading, which is about several times that of a magneto-optical recording device with a wavelength of 830 nm that is currently commercially available.

On the other hand, the unevenness of the substrate can be formed at a higher density than the reproduction resolution. At present, there is no problem in forming irregularities having a size of about 0.3 micron. This is a high NA for the fabrication of stampers used to injection mold substrates.
This is because high-precision processing is performed using the objective lens and the short wavelength gas laser. The shape of the stamper thus produced is well transferred to the substrate by optimizing the injection molding conditions. It is possible to form unevenness with higher density by using a laser with a shorter wavelength or by optimizing the conditions of the mastering process.

As described above, although it is possible to manufacture a read-only information recording medium in which irregularities are formed at a high density, it was not possible to reproduce the information.

Therefore, the present invention provides an information recording / reproducing method capable of reproducing information from a reproduction-only information recording medium having a high density of irregularities, and an information recording medium used in such an information recording / reproducing method. The purpose is to do.

[0009]

In the information recording / reproducing method of the present invention, information is reproduced by using the change in the absorption of microwaves in the uneven portion formed in advance on the information recording medium corresponding to the information. At the time of reproducing information, it is desirable to locally heat a part of the information recording medium by focusing laser light on the information recording medium using an optical head. The information recording medium used there is composed of a magnetic film and a substrate on which irregularities corresponding to the information to be recorded are previously formed. In addition, a magnetic film is formed on a substrate on which unevenness corresponding to information to be recorded is formed, and further unevenness and magnetic film corresponding to another recorded information are formed at least once.

[0010]

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 around 100 MHz to 100 GHz, 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 body is used as a sample and the magnetic body 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 shown by the following equation. Be done.

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

[0013]

[Equation 1]

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

[0015]

[Equation 2]

Where ω ₀ is the resonance frequency, M is the magnetization, and γ
Represents the gyromagnetic ratio. From these equations, the value of the resonance frequency changes depending on whether the direction of the applied magnetic field is the direction perpendicular to the magnetic film or the in-plane direction. This change occurs due to the difference between the demagnetizing field and the anisotropic magnetic field of the magnetic film. Further, this change is continuous from the direction perpendicular to the film surface to the in-plane direction, and when the direction of the applied magnetic field is inclined from the direction perpendicular to the magnetic film, the resonance frequency changes accordingly. This phenomenon is observed as a change in the resonance magnetic field when a microwave having a constant frequency is applied. Here, if the angle of the magnetic film with respect to the applied magnetic field is changed while keeping the direction of the applied magnetic field in one direction, the absorption of microwaves changes. Information can be reproduced by microwaves by changing the angle of the magnetic film with respect to the applied magnetic field according to the recorded information.

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

[0018]

[Equation 3]

It is known that this is,
It is the detection sensitivity when the sample is placed in the cavity resonator.
Here, V is the volume of the microwave cavity resonator, Q ₀ is its Q value, ΔH ₀ / H ₀ is the ratio between 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 is very sensitive to the detection of magnetic resonance,
This shows that the method 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 the microwave 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,
We have found that a high areal recording density can be achieved by heating a part of the recording medium irradiated with microwaves. FIG. 1 shows the reproducing principle. A part of the recording medium is heated by irradiation with laser light or the like. Magnetic layer
The direction of magnetization 108 of 107 is aligned in one direction beforehand.
At this time, the temperature of the recording medium rises and the magnetic layer 107
The frequency of the microwave 103 and the magnitude of the applied magnetic field 109 are set so that the magnetic resonance occurs only when is oriented in the direction perpendicular to the applied magnetic field 109. In this case, magnetic resonance occurs only in the heated region 105 of the flat portion 110. Moreover, in the inclined portion in the heated region, the magnetic field is not applied in the direction perpendicular to the film surface. In addition, the magnetization is inclined from the easy axis of magnetization. Due to these causes, magnetic resonance does not occur in the inclined portion of the heated region. On the other hand, the microwave is not absorbed in the region where the temperature has not risen because magnetic resonance does not occur. Microwave absorption occurs only in the heating region 104 when a specific condition is satisfied, so that a very high areal recording density can be obtained.

Further, the recording capacity can be increased by forming the combination of the unevenness corresponding to the recording information and the magnetic film a plurality of times. By forming a magnetic film on a substrate on which irregularities corresponding to recorded information are formed, and subsequently forming irregularities and magnetic films corresponding to different recorded information by a photo polymer process (2P method) or the like, the recorded information is recorded. Is multi-layered. Microwave reproduction is so sensitive that it is possible to make the magnetic layer very thin. Therefore, even if two or three magnetic layers are laminated, the temperature of the magnetic layer can be sufficiently increased by the optical head. Therefore, the information can be reproduced from the plurality of magnetic layers, and the recording capacity can be greatly increased.

As described above, in the information reproducing method using microwaves, the resolution in the plane direction is determined by the region where the temperature rises. Since the area where the temperature is rising can be made smaller than the light spot, it is possible to reproduce the information recorded as unevenness smaller than the light spot. Further, it becomes possible to reproduce the information from the medium in which the information is multi-layered and recorded. Therefore, the information reproducing method using the microwave can obtain a recording capacity several times or more as compared with the optical reading.

[0023]

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

Embodiment 1 FIG. 3 is a block diagram of an apparatus used for reproducing information. A Gunn diode is used as the microwave oscillation source 305. The microwave frequency is 9.3GHz,
The microwave power was set to 1 mW. A GaAs Schottky barrier diode was used as the microwave detector 307, and the signal was detected by homodyne detection. The microwave oscillated by the Gunn diode is guided to the recording medium 301 by the waveguide 306, and the microwave partially absorbed by the recording medium 301 passes through the recording medium 301 and reaches the detector 307,
It is a configuration that is converted into an electrical signal. A disk-shaped recording medium 301 is used, and is rotated at a constant angular velocity by a spindle motor 302. An optical head 304 having a laser light wavelength of 830 nm was arranged directly above the recording medium 301, and control was performed so that the light spot was focused on the magnetic layer of the recording medium 301. The laser spot diameter on the recording medium is about 1.4 microns. By forming a guide groove on the recording medium 301, the position of the light spot was controlled in the radial direction of the disc. As the recording medium 301, a transparent substrate on which a magnetic layer is formed is used, and a laser beam is emitted from the substrate side and a microwave is emitted from the opposite side. Microwave detector 307
Was arranged on the same side as the optical head 304 with respect to the recording medium 301. As a means for applying a magnetic field to the recording medium 301 during reproduction, a magnetic field applying coil 303 is arranged on the opposite side of the recording medium 301 from the optical head 304, and a desired magnetic field can be obtained by passing a desired current. It was configured.

Next, the recording medium A used here will be described. The guide groove 401 and the recording pit 402 were formed on the disk-shaped flat glass substrate by the 2P method (photo polymer process). The arrangement is shown in FIG. The spacing between the guide grooves 401 was formed to be 1.6 microns. The guide groove 401 was V-shaped and had a width of 0.4 micron. The recording pit 402 has a shape similar to that of an ellipse as shown in FIG. 4A, and a bevel-shaped inclined portion 404 is formed at the front and rear ends of the recording pit 402. A sectional view in the track direction is shown in FIG. The length of the inclined portion 404 in the track direction is 0.3 μm, and the flat portion 40
The size and interval of the recording pits 402 were adjusted so that the length of 3 was 0.3 μm repeatedly. The recording pit 402 has a depth of 0.15 micron. On this substrate, 750Å AlSiN as the first protective layer, 700Å GdDyFeCo amorphous alloy thin film as the magnetic layer, and AlSiN as the second protective layer.
The film was formed by continuously sputtering 1000 Å. When a 9.3 GHz microwave is irradiated to a sample prepared by forming this magnetic layer on a flat glass substrate, the resonance magnetic field at room temperature when a magnetic field is applied in the direction perpendicular to the film surface is 3.5 kGaus.
s, and was about 300 Gauss at 120 ° C. Also,
The easy axis of magnetization of the magnetic layer is perpendicular to the film surface, the Curie temperature is 180 ° C., and the coercive force at room temperature is 2.2 kOe.

Information was reproduced from the recording medium A by microwaves. The disk rotation speed is 1800 rpm and the disk radius is 30 mm. In this condition, 0.3 micron size information corresponds to 9.4 MHz. Laser power of optical head 2.9m
The light was focused on the magnetic layer as W and a part of the magnetic layer was heated.
A magnetic field of 300 Gauss was applied to the heated region. Here, the recording medium A was irradiated with microwaves and the absorption signal was measured with a spectrum analyzer. The evaluation conditions are a resolution bandwidth of 30 kHz and a video bandwidth of 100 Hz. The measured reproduction signal has a CN ratio at 9.4 MHz of 48.9 dB,
It was confirmed that good reproduction was possible. When only the microwave was applied while applying the magnetic field without heating by the optical head, the 9.4 MHz component was not detected in the reproduced signal. From the above results, by irradiating the microwave while heating a part of the recording medium,
It was confirmed that it is possible to reproduce magnetic information only in the heated area. Further, when the same recording medium was reproduced by the optical head, the CN ratio of the reproduced signal was 26.3 dB. From the above, it was confirmed that the reproducing method using microwaves can reproduce information from the recording pits formed with high density better than the reproducing method using light. This makes it possible to obtain a read-only medium having a recording capacity increased as compared with the conventional one.

In this embodiment, the magnetic film is GdDyFe.
Although a Co amorphous alloy thin film is used, it has been confirmed that it is also effective for other rare earth-transition metal amorphous alloys, garnet, oxides such as ferrite as a magnetic film. It is not limited to the magnetic film.

Example 2 Next, the magnetic film was changed from a perpendicular magnetization film to an in-plane magnetization film to reproduce information. The recording medium B manufactured here will be described. A polycarbonate substrate having recording pits and guide grooves formed on the substrate was used. The arrangement of the guide groove 401 and the recording pit 402 is shown in FIG. Guide groove 40
The intervals of 1 were formed to be 1.6 microns. Guide groove 40
The shape of 1 was V-shaped and its width was 0.4 micron. The recording pit 402 has a shape similar to a cone as shown in FIG. A cross-sectional view in the track direction is shown in FIG. The length of the recording pit 402 in the track direction was adjusted to 0.25 μm, and the length of the flat portion was adjusted to 0.25 μm.
The recording pit 402 has a depth of 0.15 micron. And
On this substrate, 750Å AlSiN as the first protective layer, 1500Å CoNi alloy thin film as the magnetic layer, and AlSiN as the second protective layer.
1000 Å was continuously formed into a film by a sputtering method. The CoNi alloy thin film used here is an in-plane magnetized film, and the easy axis of magnetization is tangential to the guide groove 401. This sample was prepared on a flat glass substrate with this magnetic layer.9.
When irradiated with a microwave of 3 GHz, the resonant magnetic field at room temperature when a magnetic field was applied in the direction perpendicular to the film surface was 2.2 kGauss, and was about 250 Gauss at 110 ° C.

Next, the signal from the recording medium B was reproduced by the microwave. The regenerator used in Example 1 was used. FIG. 6 is a schematic diagram of reproduction in this embodiment. Prior to reproduction, a magnetic field was applied by the ring-type magnetic head 603 to align the direction of magnetization of the magnetic film with one direction of the track, and then reproduction was performed. Disk speed 1800rp
m, disk radius 30 mm. In this condition, the 0.25 micron size information corresponds to 11.3 MHz. The laser power of the optical head was set to 2.5 mW and focused on the recording layer to heat a part of the recording layer. A magnetic field of 250 Gauss was applied to the heated region. Here, the recording medium B was irradiated with microwaves and the absorption signal was measured with a spectrum analyzer. Evaluation conditions are resolution bandwidth 30kHz, video bandwidth 1
It is 00Hz. The CN ratio of the measured reproduced signal at 11.3 MHz was 47.8 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 11.3 MHz component was not detected in the reproduced signal.

In this embodiment, a CoNi alloy thin film is used as the magnetic film, but it has been confirmed that the in-plane magnetized film other than this is also effective as the magnetic film, and the present invention is limited to this magnetic film. It is not something that will be done. In addition, Example 1
In 2 and 2, changes in the absorption of microwaves were realized by using the inclined portions of the recording pits, but it is possible to reproduce information by microwaves if a method of changing the angle of the magnetic film with respect to the applied magnetic field is used. For example, a method of forming very fine irregularities on the substrate is also effective, and the present invention is not limited to these examples.

Embodiment 3: The reproduction of information from a recording medium in which recording information by unevenness is formed in multiple layers will be described. The structure of the recording medium C used here is shown in FIG. First, the guide groove 401 and the recording pit 402 were formed on the disk-shaped flat glass substrate 701 by the 2P method. The arrangement is the same as in the second embodiment.
The spacing between the guide grooves 401 was formed to be 1.6 microns.
The guide groove 401 was V-shaped and had a width of 0.4 micron. The length of the recording pit 402 in the track direction was adjusted to 0.25 μm, and the length of the flat portion was adjusted to 0.25 μm. The recording pit 402 has a depth of 0.15 micron. On top of this, AlSiN is used as the first protective layer 703.
0 Å, 15 GdDyFeCo amorphous alloy thin film as the first magnetic layer 704
0 Å and 400 Å of AlSiN were continuously deposited as the second protective layer 705 by a sputtering method. Further, a guide groove 401 and a recording pit 402 were formed on this by the 2P method. Recording pit 40
2 and the shape of the guide groove 401 are the same as before, but the recording pit
The length of the 402 in the track direction was changed to 0.3 μm, and the length of the flat portion was changed to 0.3 μm. Then, AlSiN is 300 Å as the third protective layer 707, and the second magnetic layer 708 is
GdDyFeCo amorphous alloy thin film as 150 Å, 4th protective layer 709
As a film of AlSiN was continuously formed by sputtering to 1000 Å. The distance between the first magnetic layer 704 and the second magnetic layer 708 is 15
It was micron. The first magnetic layer 704 and the second magnetic layer 708 are magnetic films having the same composition and film thickness. When a sample prepared by forming this magnetic layer on a flat glass substrate is irradiated with microwaves of 9.3 GHz, the resonance magnetic field at room temperature when a magnetic field is applied in the direction perpendicular to the film surface is 3.0 kGauss, and at 100 ° C About 300G
It was auss. In addition, the easy axis of magnetization of the magnetic layer is perpendicular to the film surface, the Curie temperature is 180 ° C., and the coercive force at room temperature is 2.2 kOe.

Next, a signal was reproduced from the manufactured recording medium C by microwaves. First, prior to the measurement, a magnetic field of 15 kOe was applied to the recording medium C in the direction perpendicular to the substrate. The disk rotation speed is 1800 rpm and the disk radius is 30 mm. Under this condition, the 0.25 micron size information is 11.3
In MHz, 0.3 micron size information is equivalent to 9.4 MHz. First, with the laser power of the optical head being 2.7 mW, first
A part of the recording medium C was heated by focusing on the magnetic layer 704. A magnetic field of 300 Gauss was applied to the heated region. Here, the recording medium C was irradiated with a microwave having a frequency of 9.3 GHz, and a signal of the absorption was measured with a spectrum analyzer. The reproduction signal was evaluated in the same manner as in Example 1. The measured playback signal has a CN ratio of 11.3 MHz of 48.0 dB,
No 9.4 MHz signal was detected. Next, when the recording medium C was heated by condensing it on the second magnetic layer 708 with the laser power of the optical head being 3.4 mW, the CN ratio of the reproduced signal at 9.4 MHz was 4
It was 8.4 dB, and the 11.3 MHz signal was not detected as before. From the above, it was confirmed that good recording signals could be independently obtained in the recording medium having two recording layers. Then, it was confirmed that the information can be reproduced even if the recorded information by the unevenness is laminated, and the recording capacity can be increased.

Although a recording medium having two recording layers is used in this embodiment, the present invention is also effective for a recording medium having three or more recording layers, and the present invention is not limited to this embodiment. Should not be considered.

[0034]

As described above, it becomes possible to reproduce information by the unevenness formed on the substrate at a high density,
The recording capacity of the medium could be increased. It is possible to obtain a read-only medium which has a simple structure and is very inexpensive. Further, since the recording layers can be multi-layered, the recording capacity can be further increased.

[Brief description of drawings]

FIG. 1 is a principle diagram of information reproduction 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 block diagram of the information reproducing apparatus used in the first embodiment.

4A is a diagram showing the arrangement of recording pits and guide grooves on the substrate of the recording medium A used in Example 1. FIG. (b)
4A is a cross-sectional view taken along the line AA ′ of the substrate in FIG. (c) is
It is a BB 'sectional view of a board | substrate in FIG.4 (a).

5A is a diagram showing the arrangement of recording pits and guide grooves on the substrate of the recording medium B used in Example 2. FIG. (b)
FIG. 6 is a cross-sectional view of the substrate taken along the line AA ′ in FIG. (c) is
It is a BB 'sectional view of a board | substrate in FIG.5 (a).

FIG. 6 is a principle diagram of information reproduction of the present invention.

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

[Explanation of symbols]

 101 Objective Lens 102 Laser Light 103 Microwave 104 Heating Region 105 Resonance Region 106 Substrate 107 Magnetic Layer 108 Magnetization 109 Applied Magnetic Field 110 Flat Part 111 Inclined Part 301 Recording Medium 302 Spindle Motor 303 Magnetic Field Applying Coil 304 Optical Head 305 Microwave Oscillation Source 306 Waveguide 307 Microwave detector 401 Guide groove 402 Recording pit 403 Flat portion 404 Inclined portion 601 First applied magnetic field 602 Second applied magnetic field 603 Magnetic head 701 Substrate 702 1-2P resin layer 703 First protective layer 704 Fourth DESCRIPTION OF SYMBOLS 1 Magnetic layer 705 2nd protective layer 706 2nd-2P resin layer 707 3rd protective layer 708 2nd magnetic layer 709 4th protective layer

Claims (4)

[Claims] 1. An information recording / reproducing method in which an information recording medium is locally heated and at the same time a microwave is applied to the information recording medium, and information is reproduced using absorption of the microwave in the information recording medium. In the method, the information recording / reproducing method is characterized in that the information is reproduced by using the change in the absorption of the microwave in the uneven portion formed in advance on the information recording medium corresponding to the information. 2. The information recording / reproducing method according to claim 1, 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. 3. Information recording / reproducing for locally heating the information recording medium and simultaneously irradiating the information recording medium with microwaves to reproduce information by absorbing the microwaves in the information recording medium. An information recording medium used in the method, comprising: a substrate on which irregularities corresponding to information to be recorded are previously formed; and a magnetic film. 4. The information recording medium according to claim 3, wherein a concavo-convex corresponding to recording information different from the recording information is formed on a recording medium having a magnetic film formed on a substrate on which concavities and convexities corresponding to the recording information are formed. An information recording medium, wherein the magnetic recording medium and the magnetic film are formed at least once.