JPS61239421A - Composite magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent unjust use by forgery by providing high coercive force and a low Curie point and furnishing a double structure by temps. to the surface layer and the substrate layer. CONSTITUTION:The surface magnetic layer 5 has magnetic characteristics such as 50-200 deg.C Curie point and >=50e coercive force and a ferromagnetic alloy having 1,000Angstrom -1mum film thickness is used as a magnetic recording medium. The surface magnetic layer 5 and a substrate magnetic layer 3 can be independently magnetized and degaussed and both layers have the function as the recording and reproducing medium. The substrate magnetic layer 3 has H=2,000Oe and Tc=300 deg.C which is sufficiently higher than the Tc=100 deg.C of a 33at% Ni-Fe alloy film. Consequently, the recorded information of the substate magnetic layer 3 is hardly affected even when the layer is heated close to 100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a magnetic recording medium, particularly a composite magnetic recording medium used in cash cards and identification cards.

(b) Conventional technology Recently, magnetic recording and reproducing devices used for recording and reproducing magnetic cards used in transportation tickets, commuter passes, etc. have the ability to accurately check the appearance and shape of the card itself. do not have. Therefore, even a counterfeit card may be treated as a legitimate card if the information recorded on the card is correct. In addition, as a surface magnetic layer of a card, a soft magnetic alloy powder having a coercive force of several Oe or less is coated on the underlying magnetic layer to form a composite magnetic recording medium and measure the leakage of magnetic information. However, this method has the disadvantage that magnetically recorded information in the underlying magnetic layer can be easily read by applying a weak magnetic field.

(c) Problems to be Solved by the Invention The present invention aims to provide a novel composite magnetic recording medium that can prevent the above-mentioned forgery or information leakage. The magnetic recording and reproducing device to which this composite magnetic recording medium is applied was previously proposed by the applicant in Japanese Patent Application No. 93806 of 1982 (Japanese Unexamined Patent Publication No. 1983).
No. 7-20903) has been filed as "Magnetic recording and reproducing device". The present invention relates to an improvement of a magnetic recording medium used in this magnetic recording/reproducing apparatus. That is, the summary of the above invention is a magnetic recording medium which has two or more magnetic layers and these magnetic layers are laminated such that each layer has two or more types of Curie point characteristics and two or more types of coercive force. , means for performing magnetic recording and reproduction on the recording medium, and means for heating the recording medium at a predetermined temperature after reproduction by the magnetic recording and reproduction means.

means for reproducing the recording medium after the heating;
The present invention is a magnetic recording/reproducing apparatus including a circuit that performs arithmetic processing on the reproduction information before heating and the reproduction information after heating to determine whether or not the recording medium is genuine. For a magnetic recording medium to meet this purpose, it is necessary to use a ferromagnetic alloy thin film as a surface layer, which has magnetic recording characteristics such as a large coercive force and a small Curie point. In general, magnetic alloys with a low Curie point have a small magnetocrystalline anisotropy and a coercive force■. decreases. On the other hand, the thickness of the ferromagnetic alloy thin film varies from 10-3 to 1
It is known that when the thickness is reduced to O-6crn, the domain wall energy suddenly becomes large and the domain structure changes. At this time, it can be expected that the holding force will increase. Film thickness is 1
When the thickness becomes even thinner than 0-6, the magnetic energy of the Neel wall is smaller than the magnetic energy of the Zulloch wall, and a magnetic domain structure with Neel walls is formed, so that the coercive force becomes even smaller.

B) Means for Solving the Problems Based on the above-mentioned principle, the present invention aims to obtain a composite magnetic recording medium in which a surface magnetic alloy layer is a ferromagnetic alloy thin film having a low one-point Tc and a high coercive force H0. It is something. That is, the surface magnetic layer is a magnetic recording medium made of a ferromagnetic alloy having a Curie point of 50 DEG to 200 DEG C. and a coercivity of 5 Oe or more and a film thickness of 1000 DEG to 1 .mu.m.

) Example 33%atNi-F with one point Tc of about 100°C
If the e-alloy is produced by a normal melting method, the coercive force Hc at room temperature will be several Os or less, so the above purpose can be achieved;
I can't. Therefore, by depositing this alloy to an appropriate thickness using a vapor deposition method, it was possible to change the magnetic domain structure of the thin film and increase the coercive force Ha according to the principle described in the previous section. When the film is deposited to a thickness of 3000X, the holding force Hc is 406e.
By making it even thinner, it was confirmed that it could be increased to 70 δe'J. As the film thickness decreases, the saturation magnetization decreases, but 9
This is not a hindrance for this purpose. FIG. 1 shows a cross-sectional view of a composite magnetic recording medium l according to the present invention. 2 is a substrate made of plasti, resin, etc., with a ferrite-based magnetic oxide film as a base magnetic layer 3, and an isolation layer 4 thereon on which 33 at%
A Ni--Fe alloy was deposited to form the surface magnetic layer 5. It goes without saying that sputtering may be used instead of vapor deposition. Note that 6 in the figure is a surface protective layer.

(f) Effects of the invention It was confirmed that the surface magnetic layer and the underlying magnetic layer of the composite magnetic alloy film prepared in this manner can be independently magnetized and demagnetized, and that it functions as a recording/reproducing medium. did. The underlying magnetic layer is H=20000e Tc-300
° and y 33 at%Ni-Fe alloy film Tc
= It is sufficiently higher than 100°C, so even if it is heated to around 100°C, the underlying magnetic layer will hardly be affected by the recorded information. As explained above, the composite magnetic recording medium according to the present invention has a high coercive force with a low curvature, and the surface layer and the underlayer have a double structure depending on the temperature. By heating this magnetic recording medium at a temperature of , and comparing the reproduced information before heating with the reproduced information after heating, it can be determined whether the magnetic medium is genuine or not, and unauthorized use due to forgery can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a composite magnetic recording medium according to the present invention, viewed in the thickness direction. In the figure, 1... Composite magnetic recording medium according to the present invention, 2... Plastic substrate, 3... Base magnetic layer, 4... Insulating isolation layer, 5... Surface magnetic layer, 6...・Surface protective layer.

Claims (1)

[Claims] (1) Consists of two or more magnetic layers with different Curie points and coercive forces, and the surface magnetic layer has a Curie point of 50 to 200°C.
, the thickness of the film is 10 with magnetic properties such that the coercive force Hc is 5 Oe or more.
A composite magnetic recording medium characterized by being a ferromagnetic alloy thin film of 0 Å to 1 μm.