Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1998-10-13
2001-10-30
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C369S288000, C428S064200, C428S402000
Reexamination Certificate
active
06310837
ABSTRACT:
TECHNICAL FIELD
This invention relates to magnetic recording media, typically magnetic cards and a method for writing and reading data from such magnetic recording media.
BACKGROUND ART
In the recent years, magnetic cards enjoy widespread use in a variety of fields. In particular, the magnetic cards find an expanding application as rewritable or prepaid cards in which monetary information is recorded as magnetic bits of information so that the amount of money may be reduced on every use.
In this application, the safety of the card system is fatally lost if magnetic cards are not fully protected against forgery by the alteration of recorded data or counterfeit cards can be easily produced. There is a strong demand for magnetic cards having a protective function of preventing the alteration of recorded data. To meet the demand, a variety of magnetic cards have been proposed and used in practice. For example, if magnetic cards are locally provided with a region of a special material, they are difficult to counterfeit and whether they are false or true can be judged by detecting the special region. Magnetic cards with a complex layer arrangement are also known.
These magnetic cards having the protective function incorporated therein are difficult to forge or duplicate a number of counterfeit cards. However, there is still a possibility that the monetary information in an exhausted card be restored to the initial information by false alteration, for example, by rewriting the monetary information. One countermeasure is to punch holes in the card in accordance with the number of uses although this yet raises several problems that precise agreement is not expectable, punched chips are left, and repair by refilling the holes is possible. Another possible countermeasure is to record visible data corresponding to the number of uses by thermographic recording. These cards carrying visible data, however, are weak against staining because the visible data must be optically read. The falsification of the record is easy on account of visible data. Another problem is that optical readers are generally expensive. There are available no practical means which are quite effective for protection against forgery.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a magnetic recording medium which is effectively protected against forgery by the alteration of recorded information, and to provide a method for recording and reading data from the magnetic recording medium.
This and other objects are attained by any of the following constructions (1) to (19).
(1) A magnetic recording medium comprising a recording material composed of a crystalline alloy containing iron and aluminum and capable of transition from a disordered phase to an ordered phase by heating, said recording material having saturation magnetization of at least 45 emu/g in the disordered phase which is at least 35 emu/g higher than the saturation magnetization in the ordered phase.
(2) The magnetic recording medium of (1) wherein said recording material has a ratio of the saturation magnetization in the disordered phase to the saturation magnetization in the ordered phase which is at least 2/1.
(3) A magnetic recording medium comprising a recording material composed of a crystalline alloy containing iron and aluminum wherein dark regions are observable in a bright-field image by transmission electron microscopy, the dark regions accounting for 15 to 60% in areal ratio.
(4) A magnetic recording medium comprising a recording material composed of a crystalline alloy containing iron and aluminum wherein dark regions having a breadth of 10 to 200 nm are observable in a bright-field image by transmission electron microscopy.
(5) The magnetic recording medium of (4) wherein in the bright-field image of said recording material, the dark regions account for 15 to 60% in areal ratio.
(6) The magnetic recording medium of any one of (3) to (5) wherein the presence of a Fe
3
Al type crystal lattice in the dark regions is ascertainable.
(7) The magnetic recording medium of any one of (1) to (6) wherein in said recording material, the total amount of iron and aluminum is at least 90 at % and the atomic ratio Al/(Fe+Al) ranges from 0.30 to 0.45.
(8) A magnetic recording medium comprising a recording material composed of a crystalline alloy containing iron and aluminum wherein the total amount of iron and aluminum is at least 90 at % and the atomic ratio Al/(Fe+Al) ranges from 0.30 to 0.45.
(9) The magnetic recording medium of (7) or (8) wherein aluminum in said recording material is replaced by M
I
which is at least one element selected from the group consisting of silicon, germanium, tin, antimony, bismuth, molybdenum, tungsten, niobium, tantalum, titanium, zirconium, and hafnium, and the content of M
I
in said recording material is up to 10 at %.
(10) The magnetic recording medium of any one of (7) to (9) wherein iron in said recording material is replaced by M
II
which is at least one element selected from the group consisting of cobalt, nickel, manganese, chromium, vanadium, and copper, and the content of M
II
in said recording material is up to 20 at %.
(11) The magnetic recording medium of any one of (7) to (10) wherein said recording material further contains up to 10 at % of M
III
which is at least one element selected from the group consisting of boron, carbon, nitrogen, and phosphorus.
(12) The magnetic recording medium of any one of (3) to (11) wherein said recording material has saturation magnetization of at least 45 emu/g and lowers its saturation magnetization by at least 35 emu/g upon heating.
(13) The magnetic recording medium of any one of (3) to (12) wherein said recording material has a ratio of the saturation magnetization before heating to the saturation magnetization after heating which is at least 2/1.
(14) The magnetic recording medium of any one of (1) to (13) wherein said recording material is a powder of flattened particles.
(15) The magnetic recording medium of any one of (1) to (14) which is a magnetic card comprising a resinous substrate and an irreversible recording layer thereon containing said recording material.
(16) A method for carrying out writing and reading on the magnetic recording medium of any one of (1) to (15), wherein
writing is carried out by heating at least a portion of the recording material by means of a thermal head or laser beam, for changing the saturation magnetization of the recording material in an irreversible manner.
(17) The method of (16) wherein after writing, reading is carried out by detecting the magnetization of the recording material.
(18) The method of (16) wherein after writing, reading is carried out by applying dc magnetic field across the magnetic material and then detecting magnetic flux from the recording material.
(19) The method of (16) wherein after writing, reading is carried out by detecting the magnetization of the recording material while applying dc magnetic field across the magnetic material.
FUNCTION AND EFFECT
Owing to the non-rewritable recording material, the magnetic recording medium of the invention is quite difficult to falsely alter the recorded data. When applied as magnetic cards, the medium of the invention is highly safe against forgery. In addition, since the information data can be magnetically read out, a write/read equipment may be relatively inexpensive.
JP-A 77622/1996 discloses an irreversible recording medium using as a magnetic recording material an alloy wherein the ratio of the saturation magnetization in a crystalline state to the saturation magnetization in an amorphous state is 5/1 or higher. In contrast, the non-rewritable recording material used in the present invention is a crystalline alloy and is more stable than the amorphous recording material of this reference.
REFERENCES:
patent: 5277977 (1994-01-01), Tokuoka et al.
patent: 5471044 (1995-11-01), Hotta et al.
patent: 0 219 714 (1987-04-01), None
patent: 0 238 069 (1987-09-01), None
patent: 0 291 306 (1988-11-01), None
patent: 0 706 191 (
Chou Tsutomu
Fujii Mari
Ishizaka Chikara
Ito Masahiro
Karatsu Masahiro
Neyzari Ali
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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