JP5185580B2 - Information recording medium - Google Patents

Description

  The present invention relates to an information recording medium that records predetermined information and is capable of optically reading the recorded information.

  Conventionally, in the case of magnetic recording information recording media, in addition to the recording method being publicly known, data can be easily viewed using magnetic powder or the like, so that forgery or alteration is possible. There was a problem that it was easy to be done.

  As a technique for solving the problem of such a magnetic recording information recording card, a technique relating to a magneto-optical information recording medium is known (see, for example, Patent Documents 1 and 2). Magneto-optical information recording media are generally less susceptible to external magnetic fields and recorded information is less likely to change. For this reason, it is considered that the magneto-optical information recording medium can prevent counterfeiting and tampering and can improve security as compared with the magnetic recording information recording medium.

Japanese Patent Laid-Open No. 58-14306 JP-A-10-134422

  However, since the conventional magneto-optical information recording medium has a recording spot diameter as small as several tens μm according to the direction of magnetization, binary information is recorded on the recording spot. Was common. For this reason, there has been a limit in trying to increase the capacity of recorded information.

  The present invention has been made in view of the above, and an object thereof is to provide an information recording medium capable of realizing a large capacity of information to be recorded.

  In order to solve the above-described problems and achieve the object, an information recording medium according to the present invention includes a recording unit that records predetermined information, and is capable of optically reading information recorded by the recording unit. In the recording medium, the recording unit includes a plurality of recording spots including a plurality of small areas to which information is independently added and having a diameter equal to or larger than a dimensional tolerance of the information recording medium.

  In the information recording medium according to the present invention as set forth in the invention described above, the plurality of recording spots are two-dimensionally arranged.

  Further, in the information recording medium according to the present invention, in the above invention, the recording unit includes a thin film-like magnetic body, and each of the plurality of small regions included in the recording spot includes a film surface of the magnetic body. Magnetization is generated in a perpendicular direction, and information corresponding to the magnetization direction is recorded.

  In the information recording medium according to the present invention as set forth in the invention described above, the magnetic body includes a magneto-optical material that produces a magneto-optical effect.

  In the information recording medium according to the present invention as set forth in the invention described above, the magneto-optical material is an amorphous alloy of a rare earth and a transition metal.

  The information recording medium according to the present invention is characterized in that, in the above invention, the magneto-optical material is a magnetic garnet thin film.

  Further, in the information recording medium according to the present invention, in the above invention, the recording unit has an organic dye, and each of the plurality of small areas included in the recording spot corresponds to the amount of the organic dye in the area. The recorded information is recorded.

  Further, in the information recording medium according to the present invention, in the above invention, the recording unit includes a phase change material capable of crystal and amorphous phase change, and each of the plurality of small regions included in the recording spot includes: Information corresponding to the phase state of the phase change material in the region is recorded.

  In addition, the information recording medium according to the present invention is characterized in that in the above-mentioned invention, a card shape is formed.

  According to the information recording medium of the present invention, the recording unit for recording predetermined information includes a plurality of small areas to which information is independently added, and a recording spot having a diameter equal to or larger than the dimensional tolerance of the information recording medium. Since there are a plurality of units, the recording unit can record multi-level information more than binary. Therefore, it is possible to realize a large capacity of information to be recorded.

  The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described below with reference to the accompanying drawings. Note that the drawings referred to in the following description are merely schematic, and when the same object is shown in different drawings, dimensions, scales, and the like may be different.

  FIG. 1 is a diagram showing an overall configuration of an information reading system including an information recording card that is an information recording medium according to an embodiment of the present invention and an information reading device that reads information recorded by the information recording card. is there. An information reading system 100 shown in FIG. 1 includes an information recording card 1 that magnetically records predetermined information, and an information reading device 2 that optically reads information recorded on the information recording card 1.

  FIG. 2 is a diagram showing the configuration of the information recording card 1, and is a cross-sectional view taken along line AA in FIG. The information recording card 1 includes a thin base plate 11 and a recording unit 12 that is laminated on the surface of a substantially central portion of the base 11 and magnetically records predetermined information.

  The substrate 11 is realized using a resin such as polycarbonate, acrylic resin, or polyvinyl chloride. When reading information with visible light, the resin applied to the substrate 11 must be transparent.

  The recording unit 12 includes a magneto-optical effect such as an amorphous alloy (eg, TbFeCo) of a rare earth (Gd, Tb, etc.) and a transition metal (Fe, Co, etc.), a magnetic garnet thin film (eg: yttrium / iron garnet (YIG)), etc. This is realized using a magneto-optical material that generates Information recorded by the recording unit 12 can be optically read from the outside.

  Information recorded by the recording unit 12 is not rewritten such as information for identifying whether the information recording card 1 is a legitimate card or information for identifying the owner of the information recording card 1. Information is assumed, but other information can be recorded.

  FIG. 3 is a diagram showing the configuration of the recording unit 12, and is a plan view seen from the direction of arrow B in FIG. In the recording unit 12, a plurality of magnetized regions M serving as recording spots to which information to be recorded is provided are arranged in a two-dimensional square lattice. The magnetization region M generates magnetization in a direction perpendicular to the film surface, and forms a perpendicular magnetization film.

  4 to 9 are diagrams schematically showing the magnetization states that the magnetization region can take in the present embodiment. In the present embodiment, the magnetization region M is composed of two small regions m1 and m2, and the magnetization directions of the small regions m1 and m2 are determined independently.

  FIG. 4 shows a case where the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are both facing away from the front of the paper. FIG. 5 is a diagram schematically showing the direction of magnetization in the CC cross section of FIG. Hereinafter, the direction of magnetization shown in FIG. 4 is referred to as “downward”.

  FIG. 6 is a diagram showing a case where the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are both directed from the back of the paper surface, and FIG. 7 is a cross-sectional view taken along the line DD in FIG. It is a figure which shows the direction of magnetization typically. Hereinafter, the magnetization direction shown in FIG. 6 is referred to as “upward”.

  FIG. 8 is a diagram illustrating a case where the magnetization direction of the small region m1 is opposite to the magnetization direction of the small region m2. In FIG. 8, the magnetization direction of the small region m1 is downward, while the magnetization direction of the small region m2 is upward. FIG. 9 is a diagram schematically showing the direction of magnetization in the cross section taken along the line EE of FIG. The magnetization region M may be in a state in which the magnetization direction of the small region m1 is upward while the magnetization direction of the small region m2 is downward. This state is the state shown in FIG. 8 and FIG. Are the same as the states shown in FIG. 8 and FIG. 9. This point will be described in detail when the reading process in the information reading apparatus 2 is described.

  As described above, in the present embodiment, there are three different magnetization states depending on the magnetization direction of the magnetization region M. Therefore, in the present embodiment, ternary information can be written and recorded in the recording unit 12.

  The diameter of the magnetized region M does not affect the reading of the information reader 2 even if the information recording card 1 moves by the dimensional tolerance of the card (based on “JIS X 6301 identification card—physical characteristics”). The size is desirable, specifically, about 1 mm or more.

  Information writing to the magnetized region M is performed by applying laser light while applying a predetermined magnetic field from the writing light source to the magnetized region M to be written, in the same way as writing information on a conventional magneto-optical disk using laser light. It is performed by irradiating. At this time, writing is performed for each small area while masking one of the small areas m1 and m2. The mask member for masking one of the small areas is provided near the tip of the light source for writing, has a semicircular opening corresponding to the shape of the small areas m1 and m2, and is an optical axis of the light source for writing. A member that is rotatable in a direction orthogonal to the direction can be applied.

  In the information recording card 1, the size of the magnetization region M to be written (about 1 mm) is significantly larger than the magnetization region (about several tens of μm) of a normal magneto-optical disk. For this reason, in order to accurately write desired information to the magnetization region M without damaging the periphery of the magnetization region M, a considerably advanced technique is required. Therefore, the information recording card 1 according to the present embodiment is very difficult to falsify or forge the recorded information as compared with a normal magneto-optical disk or the like.

  In FIG. 3, the magnetized region M has a circular surface (film surface), but the surface of the magnetized region M may have a shape other than a circle (polygon, ellipse, etc.). Further, the arrangement of the magnetized regions M shown in FIG. 3 is merely an example, and may be arranged in a staggered pattern.

  The surface shape of the recording unit 12 may be a shape other than a square (rectangle, polygon, circle, etc.), and the arrangement position thereof can be changed.

  Further, a protective layer that has a property of transmitting light and is realized by, for example, silicon nitride may be provided around the recording unit 12. Further, a transparent UV curable resin may be applied to the surface of the recording unit 12 as a hard coat layer.

  FIG. 10 is a diagram illustrating a configuration of the information reading device 2. The information reading device 2 is a device that irradiates the information recording card 1 to be read with light and optically reads information recorded on the information recording card 1 using transmitted light of the irradiated light. Provided between the card insertion slot 20 for holding the card 1 in a stationary state, a light source 21 for projecting light to irradiate the information recording card 1, and the card insertion slot 20 and the light source 21. A linearly polarizing plate 22 that linearly polarizes light and a linearly polarized light that is provided on the side facing the linearly polarizing plate 22 across the card insertion slot 20 and transmits a component in a predetermined vibration direction of the light transmitted through the information recording card 1 A plate 23, a light receiving element 24 that receives light transmitted through the linear polarizing plate 23, and a signal processing unit 25 that performs predetermined signal processing on a signal detected by the light receiving element 24.

  The light source 21 is realized using a light emitting diode (LED). In the present embodiment, since the diameter of the magnetization region M in which information to be read is recorded is as large as the dimensional tolerance of the information recording card 1, it is not necessary to use a laser beam as the light source 21. Further, since the light emitted from the light source 21 is transmitted through the recording unit 12 of the information recording card 1, the distance between the light source 21 and the information recording card 1 and the distance between the light source 21 and the light receiving element 24 are made smaller than before. can do. As a result, the light emitted from the light source 21 reaches the light receiving element 24 without spreading too much, and optical components such as a condensing lens and a polarizing beam splitter are not necessary. Therefore, the number of parts can be reduced, and downsizing of the apparatus can be realized. Further, it is possible to realize cost reduction by not using expensive optical components.

  FIG. 11 is a plan view showing the configuration of the linearly polarizing plate 23. The linear polarizing plate 23 shown in the figure has a configuration in which two types of strip-shaped first polarizing plate 231 and second polarizing plate 232 having different transmission axes are arranged alternately along the short direction of each polarizing plate. Have Light that has passed through the same magnetization region M (indicated by a broken line in FIG. 11) of the recording unit 12 of the information recording card 1 is incident on the first polarizing plate 231 and the second polarizing plate 232 that make a pair adjacent to each other.

  FIG. 12 is a plan view showing the configuration of the light receiving element 24. The light receiving element 24 shown in the figure transmits the magnetization region M provided in the information recording card 1 and detects the light polarized by the linear polarizing plate 23. Therefore, the light receiving element 24 corresponds to each of the plurality of magnetization regions M, and the first light receiving unit 241 and the second light receiving unit 242 that detect light transmitted through the first polarizing plate 231 and the second polarizing plate 232, respectively. Are arranged on the base material in pairs. In other words, the light receiving element 24 receives the light transmitted through one magnetization region M by the first light receiving unit 241 and the second light receiving unit 242 that make a pair adjacent to each other. For this reason, the total number of the first light receiving parts 241 and the second light receiving parts 242 is twice as many as the magnetization region M. The broken line shown in FIG. 12 indicates the boundary between the first polarizing plate 231 and the second polarizing plate 232 when the linearly polarizing plate 23 is viewed on the light receiving element 24.

  As described above, the diameter of the magnetization region M of the recording unit 12 of the information recording card 1 is determined based on the dimensional tolerance of the card. For this reason, even if the magnetized region M moves by a dimensional tolerance, the correspondence relationship between the magnetized region M and the light receiving element 24 does not change and does not affect the reading of information recorded by the recording unit 12.

  FIG. 13 is a diagram schematically showing an outline of optical reading of information in the information reading apparatus 2 having the above configuration. First, the non-polarized light emitted from the light source 21 is linearly polarized by the linear polarizing plate 22. In FIG. 13, arrows L0 and the like schematically represent the vibration direction of the electric field that constitutes the light.

  The linearly polarized light having the vibration direction L0 irradiates the entire recording unit 12 of the information recording card 1 at a time and enters all the magnetization regions M at once. As shown in FIG. 14, the direction of vibration of the light incident on each magnetization region M rotates according to the magnetization direction of the magnetization region M (Faraday effect). In FIG. 14, the transmission axis P <b> 1 is the transmission axis of the linearly polarizing plate 22. Further, the transmission axis P 2 is the transmission axis of the first polarizing plate 231, and the transmission axis P 3 is the transmission axis of the second polarizing plate 232. Here, in order to accurately detect the magnetization direction of the magnetization region M, the intensity of the light detected through the first polarizing plate 231 and the intensity of the light detected through the second polarizing plate 232. It is desirable that the absolute value of the difference be equal regardless of the magnetization direction of the magnetization region M. Therefore, in the present embodiment, the angle formed by the transmission axis P1 of the linear polarizing plate 22 and the transmission axis P2 of the first polarizing plate 231 is the transmission axis P1 of the linear polarizing plate 22 and the transmission axis P3 of the second polarizing plate 232. It is set to be equal to the angle formed (in FIG. 14, this angle is α).

  For example, in FIG. 14, the vibration direction of linearly polarized light after passing through the magnetization region M (see FIGS. 4 and 5) in which both the magnetization direction in the small region m1 and the magnetization direction in the small region m2 are downward is L1. The vibration direction of the linearly polarized light after passing through the magnetization region M (see FIGS. 6 and 7) in which both the magnetization direction in the small region m1 and the magnetization direction in the small region m2 are upward is L2. The vibration directions L1 and L2 are directions rotated by the same angle θ (Faraday rotation angle) in the opposite directions on the same plane with respect to the vibration direction L0 of the linearly polarized light incident on the magnetization region M.

FIG. 15 shows transmitted light transmitted through the first polarizing plate 231 and the second polarizing plate 232 when the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are both downward. It is a figure which shows the component of. In FIG. 15, when the amplitude of the transmitted light having the vibration direction L1 is I, the intensity of the component L12 in the vibration direction parallel to the transmission axis P2 of the transmitted light is
I ² cos ² (α−θ). On the other hand, the intensity of the component L13 in the vibration direction parallel to the transmission axis P3 of the transmitted light transmitted through the magnetization region M in which the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are both downward is I ² cos ^2. (Α + θ). When the difference in intensity between the two vibration direction components L12 and L13 is ΔI,
ΔI = I ² cos ² (α−θ) −I ² cos ² (α + θ)
= I ² sin2α · sin2θ (1)
It is. On the other hand, in the case of transmitted light that has passed through the magnetization region M in which the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are both upward, the absolute value of ΔI is the absolute value of the equation (1). However, the sign of ΔI is opposite to that of the equation (1).

  Here, the Faraday rotation angle θ is an amount determined by the characteristics of the magnetization region M and the like. Therefore, it can be seen that α = 45 (degrees) is required to maximize the intensity difference ΔI. This is the case when the transmission axis P2 and the transmission axis P3 are orthogonal.

FIG. 16 shows that when the magnetization directions of the two small regions m1 and m2 of the magnetization region M are opposite (see FIGS. 8 and 9), the first polarization plate 231 and the second polarization plate 232 are transmitted, respectively. It is a figure which shows the component of the vibration direction of the performed light. In this case, since the upward magnetization and the downward magnetization cancel each other in the magnetization region M, the oscillation direction (polarization axis) of the linearly polarized light after passing through the magnetization region M changes compared with that before passing. And remains at L0. In other words, the Faraday rotation angle θ when transmitted through the magnetized region M is zero. Accordingly, when the amplitude of the transmitted light having a vibration direction L0 and I _0, the intensity of the component L02 of the parallel vibration direction to the transmission axis P2 of the transmitted light while a I ₀ ² cos ² α, of the transmitted light The intensity of the component L03 in the vibration direction parallel to the transmission axis P3 is also I ₀ ² cos ² α. Therefore, the intensity difference ΔI between the two vibration direction components L02 and L03 is zero.

  By the way, even if the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are opposite to those shown in FIGS. 8 and 9, ΔI = 0 remains unchanged. For this reason, the magnetization state in which the magnetization direction of the small region m1 and the magnetization direction of the small region m2 are opposite can be regarded as a state where all the same information is recorded regardless of the magnetization direction of each small region. .

  In this way, in the present embodiment, since ΔI takes three values depending on the magnetization direction of the magnetization region M, ternary information can be recorded in the magnetization region M.

  Light that has passed through the same magnetization region M and passed through the first polarizing plate 231 and the second polarizing plate 232 that correspond to each other is received by the first light receiving unit 241 and the second light receiving unit 242 that form a pair adjacent to each other. . Thereafter, the light received by the first light receiving unit 241 and the second light receiving unit 242 is photoelectrically converted and sent to the signal processing unit 25.

  The signal processing unit 25 calculates the intensity difference ΔI of the light transmitted through the same magnetized region M and received by the paired first light receiving unit 241 and second light receiving unit 242 according to the equation (1). A signal corresponding to one of three values (eg, -1, 0, 1) is output according to the value of ΔI.

  The intensity of light from the light source 21 is substantially uniform within the range of the magnetized region M, but is not uniform when viewed from the entire recording unit 12, and light reaching the central portion and the peripheral portion of the recording unit 12. Difference in strength occurs. In the present embodiment, since the information associated with the magnetized region M is detected using the difference in intensity of the light received by the first light receiving unit 241 and the second light receiving unit 242 that make a pair, the light intensity is The influence of non-uniformity depending on the position of the magnetization region M can be canceled by calculating the intensity difference. As a result, the magnetization direction of each magnetization region M can be accurately detected regardless of the non-uniformity of the intensity of light reaching each magnetization region M.

  The signal output from the signal processing unit 25 may be transmitted as it is to the information processing terminal, or information stored in advance in the information reading device 2 (for example, an ID for personal identification). You may make it perform collation.

  According to the embodiment of the present invention described above, each of the plurality of magnetization regions that are made of a thin-film magnetic material and generate magnetization in a direction perpendicular to the film surface of the magnetic material corresponds to the magnetization direction. Since the magnetization area has a plurality of small areas in which the diameter of the film surface is equal to or larger than the dimensional tolerance of the information recording medium and the direction of each magnetization is independently determined, the recording area is Multi-valued information can be recorded. Therefore, it is possible to realize a large capacity of information to be recorded.

  In addition, according to the present embodiment, since the magnetized regions whose film surface diameter is equal to or larger than the dimensional tolerance of the information recording medium are arranged two-dimensionally, they are significantly larger than the magnetized regions in the conventional magneto-optical system. The magnetized region can be arranged compactly. As a result, when the information reading device reads the information recorded on the information recording card, it is possible to irradiate linearly polarized light to a plurality of magnetized regions at once, such as an optical component such as a lens or a transport mechanism. Reading can be performed without using a complicated configuration.

  The best mode for carrying out the present invention has been described so far, but the present invention should not be limited by the above-described embodiment. For example, the magnetization region M may be further divided into many small regions, and the magnetization directions of the small regions may be set independently. FIGS. 17-20 is an example which shows the state which can be taken when the magnetization area | region M is divided | segmented into three small area | region m11, m12, m13. As shown in these drawings, when the magnetized region M is divided into three, four-value information can be recorded.

Generally, if the number of divisions of one magnetization region into small regions is n, the number of information (magnetization states) that can be taken in one magnetization region is n + 1. Therefore, since the number of information that can be recorded in the N magnetized regions is (n + 1) ^N , the amount of information that can be recorded increases dramatically as the value of n increases. In other words, the number of magnetization regions necessary for the recording unit to record the same amount of information is smaller as the number of divisions n into smaller regions of each magnetization region is larger.

  In the information recording medium according to the present invention, the recording portion may be formed by using an organic dye which is a recording material for an optical disc such as CD-R or DVD ± R. In this case, a plurality of small areas included in the recording spot record information corresponding to the amount of organic dye in each small area. The amount of organic dye in a small area is related to the reflectance and transmittance of light in that small area. For this reason, by adjusting the amount of the organic dye contained in each small region, the reflectance and transmittance of light in the recording spot can be changed in gradation. Therefore, it is possible to record multi-valued information for one recording spot. When adjusting the amount of the organic dye, the amount of the organic dye removed by laser light irradiation from the organic dye previously applied to the surface of the recording spot may be controlled for each small area.

  In the information recording medium according to the present invention, the recording portion is formed by using a phase change material (a material capable of crystal and amorphous phase change) that is a recording material of an optical disc such as DVD ± RW or DVD-RAM. May be. In this case, a plurality of small regions included in the recording spot record information corresponding to the phase state (crystalline phase, amorphous phase) of the phase change material included in each small region. The phase state of the phase change material in the small region is related to the reflectance and transmittance of light in the small region. Therefore, by individually adjusting the phase state of the phase change material included in each small region, the reflectance and transmittance of light in the recording spot can be changed in gradation. Therefore, it is possible to record multi-valued information for one recording spot.

  As described above, even when the recording spot of the recording portion of the information recording medium according to the present invention is formed by using a recording material of an optical disc such as a CD-R, DVD ± R, DVD ± RW, or DVD-RAM. As in the embodiment described above, it is possible to realize a large capacity of information recorded by the information recording medium.

  Note that when the recording spot is formed by using the recording material of the optical disc, it is not necessary to provide the first polarizing plate or the second polarizing plate in the information reading device.

  As is apparent from the above description, the present invention can include various embodiments and the like not described herein, and within the scope not departing from the technical idea specified by the claims. Various design changes and the like can be made.

It is a figure which shows the structure of the information reading system comprised using the information recording card | curd and information reading apparatus which concern on one embodiment of this invention. It is a figure which shows the structure of the information recording card | curd which concerns on one embodiment of this invention. It is a figure which shows the structure of the recording part with which the information recording card based on one embodiment of this invention is provided. It is a figure which shows the example (1st example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into two small areas. It is a figure which shows typically the direction of magnetization seen in the CC sectional view of FIG. It is a figure which shows the example (2nd example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into two small areas. It is a figure which shows typically the direction of the magnetization seen in the DD sectional view of FIG. It is a figure which shows the example (3rd example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into two small areas. It is a figure which shows typically the direction of magnetization seen in the EE line cross section of FIG. It is a figure which shows the structure of the information reader which concerns on one embodiment of this invention. It is a top view which shows the structure of the linearly polarizing plate with which the information reading apparatus which concerns on one embodiment of this invention is provided. It is a top view which shows the structure of the light receiving element with which the information reader which concerns on one embodiment of this invention is provided. It is a figure which shows typically the outline | summary of the reading of the information currently recorded on the magnetization area | region. It is a figure which shows rotation of the vibration direction by the magneto-optical effect (Faraday effect) of the light which permeate | transmitted the magnetization area | region. It is a figure which shows the component of the vibration direction of the light which permeate | transmitted two polarizing plates. It is a figure which shows the component of the vibration direction of the light which each permeate | transmitted the 1st polarizing plate and the 2nd polarizing plate, when the magnetization direction of two small area | regions which a magnetization area | region has reverse direction. It is a figure which shows the example (1st example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into three small areas. It is a figure which shows the example (2nd example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into three small areas. It is a figure which shows the example (3rd example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into three small areas. It is a figure which shows the example (4th example) of the magnetization state at the time of dividing | segmenting a magnetization area | region into three small areas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Information recording card 2 Information reader 11 Base material 12 Recording part 20 Card insertion slot 21 Light source 22, 23 Linearly polarizing plate 24 Light receiving element 25 Signal processing part 100 Information reading system 231 1st polarizing plate 232 2nd polarizing plate 241 1st Light receiving portion 242 Second light receiving portion M Magnetized region m1, m2, m11, m12, m13 Small region

Claims (8)

An information recording medium comprising a recording unit for recording predetermined information, capable of optically reading information recorded by the recording unit, and having a card shape,
The recording unit is
A recording spot including a plurality of small areas to which information is independently assigned, and the recording unit is not less than the dimensional tolerance of JIS X 6301 and the information recording medium moves even if the dimensional tolerance moves. An information recording medium comprising a plurality of recording spots having a diameter that does not affect the reading of an information reading device that reads information recorded by the recording medium.   The information recording medium according to claim 1, wherein the plurality of recording spots are arranged two-dimensionally. The recording unit has a thin film magnetic material,
2. Each of the plurality of small areas included in the recording spot generates magnetization in a direction perpendicular to the film surface of the magnetic material, and records information corresponding to the direction of the magnetization. 2. The information recording medium according to 2.   4. The information recording medium according to claim 3, wherein the magnetic material includes a magneto-optical material that produces a magneto-optical effect.   5. The information recording medium according to claim 4, wherein the magneto-optical material is an amorphous alloy of a rare earth and a transition metal.   5. The information recording medium according to claim 4, wherein the magneto-optical material is a magnetic garnet thin film. The recording part has an organic dye,
The information recording medium according to claim 1, wherein each of the plurality of small areas included in the recording spot records information corresponding to the amount of the organic dye in the area. The recording part has a phase change material capable of phase change between crystal and amorphous,
The information recording medium according to claim 1, wherein each of the plurality of small areas included in the recording spot records information corresponding to a phase state of the phase change material in the area.

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