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AssigneesTDK Corporation, Tokyo Magnetic Printing Co., Ltd.
InventorsTsutomu Chou, Masao Shigeta, Masahiro Karatsu, Mari Fujii, Chikara Ishizaka, Katsumi Saito, Katsuhiko Wakayama, Shohei Mimura, Masahiro Ito
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The invention is a magnetic recording medium which is effectively protected against forgery by the alteration of recorded data, and a method for carrying out writing and reading on this magnetic recording medium. The magnetic recording medium of the invention comprises a recording material composed of a crystalline alloy containing Fe and Al . In the recoding material, the total amount of Fe and Al is at least 90 at % and the atomic ratio Al/(Fe+Al) ranges from 0.30 to 0.45. The recording material changes from a disordered phase to an ordered phase by heating. The recording material has a saturation magnetization of at least 45 emu/g prior to heating and lowers its saturation magnetization by at least 35 emu/g upon heating. Dark regions are observable in a bright-field image of the recording material by transmission electron microscopy, the dark regions accounting for 15-60% of the recording material in areal ratio and having a maximum breadth of 10-200 nm.
A magnetic recording medium comprising a recording material comprising a disordered phase crystalline alloy of iron and aluminum, said recording material having a saturation magnetization of at least 45 emu/g wherein the total amount of iron and aluminum is at least 90 at %, a portion of the aluminum in said recording material is replaced by MI 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 MI in said recording material is up to 10 at %, the atomic ratio Fe/(Fe+Al+MI) ranges from 0.30 to 0.45, and said disordered phase crystalline alloy undergoes a transition to an ordered phase crystalline alloy upon heating, said ordered phase crystalline alloy having a saturation magnetization which is at least 35 emu/g lower than said disordered phase.
A magnetic recording medium comprising a recording material comprising a disordered phase crystalline alloy of iron and aluminum, said recording material having a saturation magnetization of at least 45 emu/g wherein the total amount of iron and aluminum is at least 90 at %, a portion of the iron in said recording material is replaced by MII which is at least one element selected from the group consisting of cobalt, nickel, manganese, chromium, vanadium, and copper, and the content of MII in said recording material is up to 20 at %, the atomic ratio Fe+MII/(Fe+Al+MII) ranges from 0.30 to 0.45, and said disordered phase crystalline alloy undergoes a transition to an ordered phase crystalline alloy upon heating, said ordered phase crystalline alloy having a saturation magnetization which is at least 35 emu/g lower than said disordered phase.
A magnetic recording medium comprising a recording material comprising a disordered phase crystalline alloy of iron and aluminum, said recording material having a saturation magnetization of at least 45 emu/g wherein the total amount of iron and aluminum is at least 90 at % and the atomic ratio Fe/(Fe+Al) ranges from 0.30 to 0.45, said recording material further contains up to 10 at % of MIII which is at least one element selected from the group consisting of boron, carbon, nitrogen, and phosphorus, and said disordered phase crystalline alloy undergoes a transition to an ordered phase crystalline alloy upon heating, said ordered phase crystalline alloy having a saturation magnetization which is at least 35 emu/g lower than said disordered phase.
Dependencies are inferred from the claim text.