Tdk Corporation

Nobuya Uchida

Takeshi Sakamoto

Chikara Ishizaka

Tetsuya Hidaka

Yoshitomo Tanaka

Kazuhito Yamasawa

Akira Fukuno

Gouichi Nishizawa

Akio Nakata

Yasuyuki Nakayama

Atsushi Oido

A rare-earth magnet having a protective film for enhancing a corrosion resistance is provided. The protective film is a three-layer film including a first protective layer with a crystalline structure &#x3b1; (for example, a polycrystalline structure), a second protective layer with a crystalline structure &#x3b2; (for example, a columnar-crystalline structure), and a third protective layer with the crystalline structure &#x3b1; from the side near a magnet body. Since the adjoining first and second protective layers have different crystalline structures from each other, and the adjoining second and third protective layers have also different crystalline structures from each other, compactness among the three layers in the protective film may be improved. Therefore, development of a pinhole is restrained, and corrosion of the protective film can be restrained.

Rare-earth magnet

A rare earth magnet having excellent corrosion resistance is provided. It has a magnet body () containing a rare earth element, and a protective film () formed on the magnet body (). In the protective film (), a first protective film (), a second protective film () and a third protective film () are laminated in this order from the side of the magnet body (). These are in a polycrystalline state and composed of a metal plated film, for example. The first protective film () and the third protective film () have a smaller mean crystal grain size than that of the second protective film (). Microcrystallization of the first protective film () can improve the density of the interface between the protective film () and the magnet body (), and decrease the number of pinholes.

Rare earth magnet

A method for manufacturing an R-T-B system rare earth permanent magnet that is a sintered body comprising a main phase consisting of an RTB phase (wherein R represents one or more rare earth elements (providing that the rare earth elements include Y), and T represents one or more transition metal elements essentially containing Fe, or Fe and Co), and a grain boundary phase containing a higher amount of R than the above main phase, wherein a product that is rich in Zr exists in the above RTB phase, the above manufacturing method comprising the steps of: preparing an R-T-B alloy containing as a main component the RTB phase and also containing Zr, and an R-T alloy containing R and T as main components, wherein the amount of R is higher than that of the above R-T-B alloy; obtaining a mixture of the R-T-B alloy powder and the R-T alloy powder; preparing a compacted body with a certain form from the above mixture; and sintering the above compacted body, wherein, in the above sintering step, the above product is generated in the above RTB phase.

Method for manufacturing R-T-B system rare earth permanent magnet

An R&mdash;T&mdash;B system rare earth permanent magnet, which is a sintered body comprising: a main phase consisting of an R T B phase (wherein R represents one or more rare earth elements (providing that the rare earth elements include Y), and T represents one or more transition metal elements essentially containing Fe, or Fe and Co); and a grain boundary phase containing a higher amount of R than the above main phase, wherein a product that is rich in Zr exists in the above R T B phase. The product that is rich in Zr has a platy or acicular form. The R&mdash;T&mdash;B system rare earth permanent magnet containing the product enables to inhibit the grain growth, while keeping a decrease in magnetic properties to a minimum, and to obtain a wide suitable sintering temperature range.

R-T-B system rare earth permanent magnet

In the manufacture of a single crystal film by epitaxial growth method, defects such as cracking are avoided by increasing the deviation of the lattice constant of the resulting film in the direction of growth from the substrate. Preferably, the deviation is increased at the rate of (0.4.about.9).times.10.sup.-4 %/.mu.m.

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Tokyo, Japan

Nobuya Uchida