JPH0950654A - Magnetic recording medium and magnetic recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium which effectively prevents forgery by altering the recorded information and to obtain a recording and reproducing method of this magnetic recording medium. SOLUTION: This magnetic recording medium has a recording material 3 comprising such an alloy having a ratio of (saturation magnetization in a crystalline state)/(saturation magnetization in an amorphous state) of >=5, and the recording material 3 contains Mn. For recording, at least a part of the recording material is crystallized by heating and cooling it with a thermal head or laser light. For reproducing, the crystallized recording material is magnetized with a DC magnetic field and then magnetization of the recording material is detected by a magnetic head, or the magnetization of the crystallized recording material is detected while a DC magnetic field is impressed on the crystallized recording material to magnetize it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic card and a magnetic recording / reproducing method.

[0002]

2. Description of the Related Art In recent years, magnetic cards have become very popular and are used in various fields. In particular, applications to cards (prepaid cards) in which amount information or the like is recorded as magnetic information and the amount is subtracted and rewritten each time they are used, are expanding.

In this application, it is easy to falsify a magnetic card due to falsification of recorded information or to forge the card itself.
This significantly reduces the security of the system. For this reason, a magnetic card having a protection function for preventing tampering of information has been demanded, and various magnetic cards have been proposed and put into practical use accordingly. For example, forming a region made of a special material on a part of a magnetic card makes it difficult to forge the card itself, or detects the region to determine the authenticity of the card, and complicates the layer structure of the card. And so on.

[0004] Although it is difficult to forge or duplicate a magnetic card employing these protection functions in large quantities, the used card information can be altered by, for example, rewriting the amount information of one card. Could be returned to the initial amount information. As a countermeasure, there is a method of punching with a punch according to the number of uses. However, this method has problems that it cannot cope finely, that a scrap is generated, and that the hole is filled and repaired. In addition, it is conceivable to record visible information in accordance with the frequency of use by thermal recording or the like. However, since visible information needs to be read optically, there is a problem that it is susceptible to dirt. In addition, since the information is visible information, falsification of the record is easy. Another problem is that the optical reader is expensive. As described above, there is no practically extremely effective means for preventing tampering.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium capable of effectively preventing alteration of recorded information due to tampering, and a method for recording and reproducing information on and from the magnetic recording medium. is there.

[0006]

This and other objects are achieved by any one of the following constitutions (1) to (9). (1) A magnetic recording medium comprising a recording material made of an alloy having a (saturation magnetization when crystalline) / (saturation magnetization when amorphous) of 5 or more, wherein the recording material contains Mn. (2) The recording material is Mn and M (M is Ge, A
The magnetic recording medium according to (1) above, which contains at least one element selected from the group consisting of 1, B, C, Ga, Si and Cr. (3) 300 when the saturation magnetization of the recording material is amorphous
The magnetic recording medium of (1) or (2) above, which is G or less. (4) 200 when the saturation magnetization of the recording material is crystalline
The magnetic recording medium according to any one of (1) to (3) above, which is G or more. (5) The magnetic recording medium according to any one of (1) to (4), wherein the crystallization temperature of the recording material is 100 to 400 ° C. (6) The magnetic recording medium according to any one of the above (1) to (5), wherein the recording material is a ribbon, a thin film, or a powder. (7) The magnetic recording medium according to any one of (1) to (6) above, which is a magnetic card having an irreversible recording layer containing the recording material on a resin substrate. (8) The above (1) to (7) having a magnetic recording layer on a substrate
Any one of the magnetic recording media. (9) A method of recording and reproducing on or from the magnetic recording medium according to any one of (1) to (8), wherein the recording is performed by heating and cooling with a thermal head or laser light. When crystallizing and reproducing at least part of the material, the crystallized recording material is magnetized by applying a DC magnetic field and then the magnetization of the recording material is detected with a magnetic head, or the crystallized recording material is applied with a DC magnetic field. A magnetic recording / reproducing method in which the magnetization of a recording material is detected while being magnetized.

[0007]

Specific Structure The specific structure of the present invention will be described in detail below.

The recording material of the magnetic recording medium of the present invention records / reproduces information by utilizing the change in the saturation magnetization of 4πMs due to the phase change. This recording material has a value of (4πMs when crystalline) / (4πMs when amorphous) is 5 in a normal operating temperature range (for example, −10 to 40 ° C.).
Or more, preferably 10 or more. If this ratio is too small, it becomes difficult to read the recorded information.
Further, this recording material has an amorphous state of 4πMs of preferably 300 G or less, more preferably 100 G or less, further preferably 50 G or less, and 4πMs when crystalline.
Ms is preferably 200 G or more, more preferably 500
G or more. If 4πMs in an amorphous state is too large or 4πMs in a crystalline state is too small, it becomes difficult to read recorded information.

In the recording / reproducing method described later, when reproducing is performed while applying a DC magnetic field to the recording material, the coercive force in the crystalline state is not particularly limited, and even a soft magnetic material is a hard magnetic material. However, the magnetization may be within a range that does not make the magnetization difficult.

The crystallization temperature of the recording material is preferably 10
The temperature is set to 0 to 400 ° C, more preferably 150 to 300 ° C. If the crystallization temperature is too low, it becomes unstable with respect to heat, resulting in low reliability. Further, the vicinity of the heating area is easily affected, and accurate recording becomes difficult. If the crystallization temperature is too high, the heating temperature required for recording becomes high and it becomes difficult to use a resin with low heat resistance for the substrate,
In addition, the recording device becomes expensive.

The Curie temperature of the recording material is not particularly limited as long as it is higher than the temperature during reproduction.

The recording material used in the present invention is an alloy containing Mn. Specifically, in addition to Mn, M (M is at least one element selected from the group consisting of Ge, Al, B, C, Ga, Si and Cr) is contained as a metalloid element. preferable. By including the element M, the above-mentioned change from amorphous to crystalline becomes easy,
Further, it becomes easy to set the crystallization temperature within the preferable range. The use of Ge or Al of M is preferable because the saturation magnetization is high, and the use of Ge is particularly preferable because the crystallization temperature is low. When Al and / or Si is added to Ge, an extremely high saturation magnetization is obtained. In addition, since the addition of Al and / or Si significantly reduces the saturation magnetization before heating, these additions contribute to an increase in the ratio of the saturation magnetization before and after heating. In this case, there is no particular lower limit to the amount of Al + Si added, but it is usually preferable to set it to 0.1 atom% or more. Further, the addition amount of Al is preferably 6 atomic% or less, S
The addition amount of i is preferably 10 atomic% or less, and Al +
It is preferable that Si does not exceed 12 atomic%. Al and S
If the addition amount of i is too large, the saturation magnetization after heating will be rather low.

In the present invention, the crystallization mechanism of the recording material is not particularly limited, but in the above-mentioned alloy containing Mn, in general,
It is considered that the compound of Mn and the other element is precipitated and crystallized, thereby increasing the saturation magnetization. For example, when Ge is included, at least a ferromagnetic Mn ₅ Ge ₃ phase is precipitated. In the case of an alloy containing Mn and Al as main components, it is considered that at least the ferromagnetic Mn ₅₅ Al ₄₅ phase is precipitated.

The preferable range of the Mn content in the alloy depends on the type of M contained in the alloy, so it may be appropriately determined so as to realize the above-mentioned action and effect.
It may be 40 to 80 atomic%, but for example, Mn-Ge
In the case of an Mn—Ge-based alloy mainly composed of Mn and Ge, such as an alloy, Mn—Ge—Al alloy, and Mn—Ge—Si alloy, the Mn content is preferably 40 to 80 atom%, more preferably 45. ˜75 at%, the Mn content in the case of Mn—Al alloy is preferably 45 to 60 at%,
More preferably, it is 50 to 55 atomic%.

The form of the recording material is not particularly limited, and may be, for example, a ribbon, a thin film, a powder, or the like. For example, when applied to a magnetic card, a thin strip of an amorphous recording material is prepared by a liquid quenching method such as a single roll method, and is attached to the surface of a substrate, or a thin film forming method such as a sputtering method or a vapor deposition method. A thin film of the amorphous recording material may be formed on the surface of the substrate, or a powder obtained by crushing a thin ribbon of the amorphous recording material may be bound with a binder and applied. When the recording material is in powder form, the particle shape is preferably flat.
If flat particles are used, the surface properties of the coating film will be good, and the magnetic recording / reproducing characteristics and the thermal conductivity upon heating will be good.

FIG. 1 shows a structural example when the present invention is applied to a magnetic card. The magnetic card 1 shown in FIG. 1 has an irreversible recording layer 3 and a magnetic recording layer 4 on a resin base 2. The irreversible recording layer 3 is an area containing the above-mentioned recording material, and the magnetic recording layer 4 is an area containing a magnetic recording material used in a normal magnetic recording medium.

When recording on the irreversible recording layer 3, after heating the recording material with a thermal head or laser light,
After cooling, at least a part of the recording material is crystallized in a predetermined pattern to improve saturation magnetization. When reproducing, the crystallized recording material is magnetized by applying a DC magnetic field and then the magnetization of the recording material is detected by a magnetic head, or the recording material is magnetized by applying a DC magnetic field while Detect magnetization. The reproduction sensitivity can be improved by performing reproduction while applying a DC magnetic field to the recording material.

The portion of the irreversible recording layer 3 which is not crystallized during recording and remains amorphous is not magnetized or has a small magnetization, so that the magnetization pattern corresponding to the heating pattern during recording can be detected during reproduction. . The crystallized portion of the irreversible recording layer 3 cannot be amorphized again. The recording material itself can be made amorphous by melting and quenching, but when such heating is performed, the resin base 2 burns. Therefore, the information recorded on the irreversible recording layer 3 cannot be rewritten, and the information can be prevented from being falsified.

The information recorded on the irreversible recording layer 3 is not particularly limited. For example, as shown in FIG.
When used as a normal prepaid card in combination with a general prepaid card, information necessary for a magnetic card is generally recorded on the magnetic recording layer 4 in addition to the amount of money and the frequency, and the irreversible recording layer 3 is recorded on the magnetic recording layer 4. Among the recorded information, information that needs to be rewritten each time it is used, such as an amount or a frequency, is recorded. Each time such information is rewritten in the magnetic recording layer 4, the information is additionally recorded in the irreversible recording layer 3. Even if the information in the magnetic recording layer 4 has been tampered with, the information in the irreversible recording layer 3 cannot be rewritten.

The information recorded on the irreversible recording layer 3 is not limited to this, and for example, an ID code as the unique data of the magnetic card may be recorded. In this case, if the information recorded on the magnetic recording layer 4 is encrypted with this ID code, the contents of the magnetic recording layer 4 of this magnetic card are copied to the magnetic recording layer of another magnetic card having another ID code. Even if it does, it becomes impossible to read out the legitimate information. According to the present invention, a unique ID code can be recorded on each card, and the card cannot be tampered with. Therefore, the effect of preventing forgery by duplication is extremely high.

In general, a magnetic recording medium has an advantage that information can be easily recorded and the recorded information can be rewritten, but it has a drawback that information can be easily tampered with in a magnetic card application. On the other hand, in the magnetic recording medium of the present invention, as described above, it is extremely difficult to tamper with information and, unlike optical reading, information can be read magnetically, so that the recording / reproducing apparatus can be inexpensive. The recording material used in the present invention has high recording sensitivity because it can be crystallized at a relatively low temperature. Therefore, recording is easy even with a thermal head having lower energy than a laser beam.

A resin protective layer or an inorganic protective layer may be provided on the irreversible recording layer 3 and the magnetic recording layer 4, if necessary. Further, the present invention is not limited to the embodiment shown in FIG. 1, and the irreversible recording layer 3 and the magnetic recording layer 4 may be formed so as to at least partially overlap, and in some cases, the magnetic recording layer 4 may not be provided.

[0023]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 A magnetic paint in which Ba ferrite powder (coercive force of 2750 Oe) was dispersed on one surface of a polyimide substrate having a thickness of 150 μm had a thickness of 1 after drying.
It was applied so as to have a thickness of 2 μm, oriented in a magnetic field, and then dried to form a magnetic recording layer. On this magnetic recording layer, a thickness of 3μ
An m 2 intermediate protective layer (acrylic resin) was formed, and an irreversible recording layer having a composition shown in Table 1 was formed on the intermediate protective layer to a thickness of 500 nm by the high frequency multi-source simultaneous sputtering method. The sputtering was performed in an Ar gas atmosphere of 5 × 10 ^-1 Pa for 20 minutes. Next, a protective layer made of an ultraviolet curable resin was formed to a thickness of 2 μm on the irreversible recording layer and punched to a card size to obtain a magnetic card.

At the time of sputtering, an irreversible recording layer having a thickness of 500 nm was simultaneously formed directly on the polyimide substrate to prepare a measurement sample.

When the crystallinity of the irreversible recording layer of each measurement sample was examined by an X-ray diffraction method, it was confirmed that no diffraction peak showing crystals was observed and the crystal was amorphous.

The saturation magnetization 4πMs of the irreversible recording layer of each measurement sample was measured at a maximum applied magnetic field strength of 10.0 kOe at room temperature using a VSM (sample vibration type magnetometer).

Next, each sample was heated to the temperature shown in Table 1 at a temperature rising rate of 10 ° C./min and cooled, and then the saturation magnetization 4πMs was measured again by VSM. When the crystallinity of the irreversible recording layer after heating was examined by an X-ray diffraction method,
Diffraction peaks showing crystals were observed in all the samples.

The X-ray (Cu-Kα ray) diffraction charts of Sample No. 105 before and after heating are shown in FIG.
And FIG. In addition, the X-ray (Cu-Kα ray) diffraction chart of Sample No. 201 before and after heating
They are shown in FIGS. 4 and 5, respectively. From these charts, it can be seen that each sample was crystallized by heating.
And in sample No. 105, it turns out that the Mn ₅ Ge ₃ phase is precipitated. Further, in sample No. 201, it is considered that the Mn ₅₅ Al ₄₅ phase is precipitated.

4πM before and after heating each sample
s is shown in Table 1. Further, graphs showing the relationship between the applied magnetic field strength H and the magnetization M for typical samples are shown in FIGS. 6 to 9 before and after heating, respectively. 6 is sample No. 105 (heating temperature 300 ° C.), FIG. 7 is sample No. 201 (heating temperature 400 ° C.), FIG. 8 is sample No. 303 (heating temperature 400 ° C.), and FIG. 9 is sample
No. 403 (heating temperature 400 ° C.).

[0031]

[Table 1]

It is clear from Table 1 that the recording material used in the present invention is crystallized at a low temperature, and the crystallization significantly improves the saturation magnetization.

The irreversible recording layer of each sample was replaced with DSC.
Thermal analysis with a (scanning calorimeter) was performed to examine the exothermic peak associated with crystallization. Sample Nos. 101 to 105 had 240 to 300 ° C, and sample No. 201 had 400 ° C.
Hereinafter, sample Nos. 301 to 307 and sample No.
It was 240-300 degreeC in 401-407.

Next, printing was performed with a thermal head under the condition of printing energy of 1.0 mJ / dot from the protective layer side of the magnetic card having the irreversible recording layer having the same composition as each of sample Nos. 105, 201 and 303. When the crystallinity of the area heated by the thermal head was examined by the X-ray diffraction method, crystallization was observed. In addition, when the saturation magnetization of 4πMs was measured by VSM, sample No. 1
No. 05 has 1150 G, sample No. 201 has 740 G, and sample No. 303 has 3300 G
G. The reason why 4πMs in this case is lower than that in Table 1 is considered to be that amorphous and crystalline are mixed according to dot-shaped heating by the thermal head.

Next, after applying a DC magnetic field to the area of these magnetic cards where the thermal head has been heated by the magnetic head to such an extent that the lower magnetic recording layer is not magnetized, the magnetic field is magnetically read at a reading speed of 314 mm / sec. When reading was performed with the head, a reproduction output was obtained. sample
A reproduction output waveform graph of No. 303 is shown in FIG. In FIG. 10, the large-amplitude signal on the left side of the center is the reproduction output generated by the dot-shaped heating. In FIG. 10, the horizontal direction is time and one division is 20 ms, and the vertical direction is output and one division is 20 mV.

An aging test in which each sample having an irreversible recording layer in an amorphous state was left at 60 ° C. for 140 hours, no crystallization of the irreversible recording layer was observed and the reliability was high. Proved expensive.

[0037]

Since the magnetic recording medium of the present invention has a non-rewritable recording material, it is extremely difficult to tamper with the recorded information. Therefore, when applied to a magnetic card, the magnetic recording medium is highly safe and moreover Since the reading can be performed magnetically, the recording / reproducing apparatus can be inexpensive.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration example when a magnetic recording medium of the present invention is applied to a magnetic card.

FIG. 2 is an X-ray diffraction chart of a recording material (Mn—Ge alloy) of the present invention before heating.

FIG. 3 is an X-ray diffraction chart after heating of the recording material (Mn—Ge alloy) of the present invention.

FIG. 4 is an X-ray diffraction chart of a recording material (Mn—Al alloy) of the present invention before heating.

FIG. 5 is an X-ray diffraction chart after heating of the recording material (Mn—Al alloy) of the present invention.

FIG. 6 is a graph showing the relationship between the applied magnetic field strength H and the magnetization M before and after heating the recording material (Mn—Ge alloy) of the present invention.

FIG. 7 is a graph showing the relationship between applied magnetic field strength H and magnetization M, before and after heating of the recording material (Mn—Al alloy) of the present invention.

FIG. 8 is a graph showing the relationship between applied magnetic field strength H and magnetization M before and after heating the recording material (Mn—Ge—Al alloy) of the present invention.

FIG. 9 is a graph showing the relationship between the applied magnetic field strength H and the magnetization M, before and after heating of the recording material (Mn—Ge—Si alloy) of the present invention.

FIG. 10 is a reproduction output waveform graph of the magnetic card.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic card 2 Substrate 3 Irreversible recording layer 4 Magnetic recording layer

Claims (9)

[Claims] 1. A magnetic recording medium having a recording material made of an alloy having a (saturation magnetization when crystalline) / (saturation magnetization when amorphous) of 5 or more, wherein the recording material contains Mn. . 2. The recording material comprises Mn and M (M is
Magnetic recording medium according to claim 1, which is at least one element selected from the group consisting of Ge, Al, B, C, Ga, Si and Cr. 3. The magnetic recording medium according to claim 1, wherein the saturation magnetization of the recording material is 300 G or less when it is amorphous. 4. The magnetic recording medium according to claim 1, wherein the saturation magnetization of the recording material is 200 G or more when crystalline. 5. The crystallization temperature of the recording material is 100-4.
The magnetic recording medium according to any one of claims 1 to 4, which has a temperature of 00 ° C. 6. The magnetic recording medium according to claim 1, wherein said recording material is in the form of a ribbon, a thin film or a powder. 7. A magnetic recording medium according to claim 1, which is a magnetic card having an irreversible recording layer containing said recording material on a resin base. 8. A magnetic recording layer on a substrate.
7. The magnetic recording medium according to any one of 7. 9. A method of recording and reproducing on the magnetic recording medium according to claim 1, wherein the recording material is heated and cooled by a thermal head or a laser beam at the time of recording. When at least a part of the magnetic field is crystallized and reproduced, the crystallized recording material is magnetized by applying a DC magnetic field, and then the magnetization of the recording material is detected by a magnetic head, or the crystallized recording material is applied by applying a DC magnetic field. A magnetic recording / reproducing method for detecting the magnetization of a recording material while magnetizing.