Fuji Photo Film Company, Limited

Japan Broadcasting Corporation

Koji Sasazawa

Tatsuji Kitamoto

Tadashi Yasunaga

Goro Akashi

Akio Yanai

Shin-ichiro Dezawa

Masaaki Fujiyama

Yasuyuki Yamada

Naoto Abe

Makoto Nagao

Nobuo Yamazaki

Nobutaka Yamaguchi

Shigeo Komine

Kouichi Masaki

Satoru Takayama

Makoto Funabashi

Shin-Ichiro Dezawa

Hotaka Minaguchi

Mahito Shimizu

Shinichiro Dezawa

Hiromichi Shibaya

A magnetic recording medium providing a high reproducing output and a high C/N over a wide recording frequency region is disclosed. The magnetic recording medium comprises a non-magnetic substrate and a lower magnetic layer, a non-magnetic intermediate layer and an upper magnetic layer on the substrate in this order so that the ratio of the non-magnetic intermediate layer thickness (t) to the upper magnetic layer thickness (d), i.e., (t/d), is within the range of 0.1/1 to 0.3/1.

Magnetic recording medium

A method and apparatus for producing a magnetic recording medium having an improved durability with a simple process. Nitrogen molecules and/or nitrogen atoms in an excited state are applied to a nonmagnetic substrate simultaneously with an iron vapor flow and an ion flow. The resulting magnetic recording medium has superior corrosion resistance and can be produced at a high film forming rate, and is especially suitable for high density recording because of its high coercive force.

Method for producing magnetic recording medium

A method for magnetic recording and reproduction comprising the steps of: (1) magnetically multiple-recording signals on a magnetic recording medium comprising a support having thereon an upper magnetic recording layer comprising barium ferrite having an increased coercive force at 60.degree. C. or more and a lower magnetic recording layer comprising at least one of chromium dioxide and Co-modified iron oxide, having a decreased coercive force at 60.degree. C. or more, disposed between said upper magnetic recording layer and said support; (2) heating said magnetic recording layers prior to reproduction due to a reproducing head; and (3) reproducing said magnetically recorded signal from said heated magnetic recording medium which is multiple-recorded.

Magnetic recording medium and method for magnetic recording and

A durable, rust- and scratch-resistant magnetic recording medium coated thereon a thin ferromagnetic film comprising an iron oxide nitride, wherein said film is an aggregation of pillar particles of said iron oxide nitride, said particles having a higher nitrogen content on their surface than inside the particles.

A method for producing a thin-film magnetic recording medium having an improved corrosion resistance and which permits production of the medium at a high speed. A magnetic material vapor flow from an evaporation source and a gas or ion flow are applied to a nonmagnetic base in an evaporation chamber and the two flows reacted with each other to form the thin-film magnetic layer on the nonmagnetic base. During this process, the expression P.sub.1 /P.sub.0 .ltoreq.0.1 is maintained, wherein P.sub.0 represents the degree of vacuum in the evaporation chamber, under a first condition where only the gas or ion flow is applied after the pressure in the chamber has been reduced to a predetermined degree of vacuum, and P.sub.1 represents the degree of vacuum in the chamber under a second condition where the magnetic material vapor flow is applied to the nonmagnetic base simultaneously with the gas or ion flow. The rate of formation of the thin-film magnetic layer is 200 .ANG./sec or more on the average.

Method for producing thin-film magnetic recording medium

A durable, weather-resistant and anti-corrosive magnetic recording medium is disclosed, which comprises a non-magnetic support having coated thereon a thin film type magnetic layer comprising iron, nitrogen oxygen and at least one element selected from the group consisting of titanium, silicon, aluminum and tantalum.

A method for producing a magnetic recording medium having improved corrosion resistance and durability. A magnetic metal thin film is formed on a nonmagnetic substrate. The substrate then is exposed to a glow discharge atmosphere, and immediately thereafter a protective lubricant layer is deposited over the magnetic metal thin film.

Method for producing magnetic recording media

A process for producing a cobalt-containing ferromagnetic iron oxide powder suitable for magnetic recording which comprises

Process for producing cobalt-containing ferromagnetic iron oxide powder

A magnetic iron oxide having a large coercive force and an improved squareness ratio prepared by coating the surface of needle-like particles of magnetic iron oxide with a cobalt compound, placing the coated iron oxide particles in a unidirectionally oriented magnetic field thereby orienting the particles in the direction of the magnetic field, and heat-treating the needle-like particles in this state with the application of an external magnetic field, or heat-treating the needle-like particles in a magnetized state.

Process for preparing magnetic iron oxide and magnetic iron oxide

A magnetic Fe oxide containing Co, and optionally, a divalent metal, in which the oxidation degree indicated by the following formula ranges from about 30% to 80%; ##EQU1## wherein y is the amount of the Co, plus the divalent metal if present, in atomic % contained in the magnetic Fe oxide, and R is the ratio of the divalent Fe ion to the total Fe ions; and a process for producing a magnetic Fe oxide containing Co, and optionally, a divalent metal, and having an oxidizing degree of about 30 to 80%, which comprises dehydrating and reducing goethite containing Co, and optionally, the divalent metal, to obtain magnetic containing Co, and optionally, a divalent metal, and oxidizing gradually the magnetite at a relatively low temperature of lower than about 100.degree. C.

Process for producing magnetic FE oxide

In a process for producing a ferromagnetic powder having a high coercive force which comprises adding an aqueous solution containing Co.sup.+2 ions, or both Co.sup.+2 ions and another cation(s), and an alkali solution to a suspension of a ferromagnetic iron oxide containing the metal(s) given by these ion(s), the improvement wherein said ferromagnetic iron oxide is treated with a reducing agent prior to the preparation of the suspension.

Process for producing ferrogmagnetic iron oxide powder comprising a

In a process for producing ferromagnetic powder which comprises adding an aqueous solution containing Co.sup.+2 ions, with or without another cation or cations, and an alkali solution to a suspension of ferromagnetic iron oxide, and heating the mixture to produce ferromagnetic iron oxide containing the metal provided by such an ion (s), the improvement wherein the heating is carried out in the presence of an oxidizing agent.

Process for producing ferromagnetic powder

A Co- and Fe-containing ferromagnetic iron oxide powder having a high coercive force and improved stability to heat and pressure is produced by adding an aqueous alkali solution, an aqueous solution containing Co.sup.+2 ions, and an aqueous solution containing not more than 1 equivalent, based on the Co.sup.+2 ions, of Fe ions to a suspension of ferromagnetic iron oxide, and heating the mixture at a temperature of at least 80.degree. C in the presence of an oxidizing agent. The ferromagnetic iron oxide powder is especially suitable for producing magnetic recording media.

Process for producing cobalt- and iron-containing ferromagnetic powder

Co- and Fe-containing ferromagnetic iron oxide powder having a high coercive force and improved stability to heat and pressure is produced by adding an aqueous alkali solution, an aqueous solution containing Co.sup.+2 ions, and an aqueous solution containing not more than 1 equivalent, based on the Co.sup.+2 ions, of Fe.sup.+3 ions to a suspension of a ferromagnetic iron oxide, and heating the mixture at a temperature of at least about 80.degree. C, preferably 90.degree. to 105.degree. C. The ferromagnetic iron oxide powder is especially suitable for producing magnetic recording media.

A process for stabilizing a ferromagnetic material comprising heat-treating a needle-like ferromagnetic material represented by the formula MO.sub.x wherein M is a ferromagnetic metal ion or a ferromagnetic non-metal ion and another metal ion, and x is the degree of oxidation which ranges from 1.36 to 1.47, and containing at least 0.5 atom % Co, at a temperature of at least about 40.degree. C, and a process for stabilizing a magnetic recording member comprising heat-treating a magnetic recording member produced by providing a ferromagnetic recording layer comprising (a) a ferromagnetic material represented by the formula MO.sub.x wherein M and x are the same as defined above, and containing at least 0.5 atom % Co, and (b) a binder, on a support, at a temperature of at least about 40.degree. C.

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Kanagawa, Japan

Koji Sasazawa