US 7,553,561 B2
Rare earth magnet
Takeshi Sakamoto, Tokyo (Japan); Nobuya Uchida, Tokyo (Japan); Yoshitomo Tanaka, Tokyo (Japan); and Yasuyuki Nakayama, Tokyo (Japan)
Assigned to TDK Corporation, Tokyo (Japan)
Appl. No. 10/566,213
PCT Filed Jul. 19, 2005, PCT No. PCT/JP2005/013240
§ 371(c)(1), (2), (4) Date Jan. 27, 2006,
PCT Pub. No. WO2006/009137, PCT Pub. Date Jan. 26, 2006.
Claims priority of application No. 2004-210451 (JP), filed on Jul. 16, 2004.
Prior Publication US 2008/0053573 A1, Mar. 06, 2008
Int. Cl. B32B 19/00 (2006.01)
U.S. Cl. 428—692.1  [428/800; 428/680; 428/679] 3 Claims
OG exemplary drawing
 
1. A rare earth magnet that has a magnet body containing a rare earth element and a protective film disposed on the magnet body,
the protective film consisting of a three-layer structure comprising:
a first protective film that is in a microcrystalline state;
a second protective film that is in a columnar crystal state and has a larger mean crystal size than that of the first protective film; and
a third protective film that is in a microcrystalline state and has a smaller mean crystal grain size than that of the second protective film;
wherein:
the first protective film, the second protective film and the third protective film are disposed sequentially from the side of the magnet body;
the first protective film as an undermost layer covers a surface of the magnet body and is covered by the second protective film;
the second protective film as an intermediate layer covers a surface of the first protective film and is covered by the third protective film;
the third protective film as an uppermost layer covers a surface of the second protective film and is exposed;
the first protective film and the third protective film have a mean crystal grain size of 0.5 μm or less; and
the second protective film has a mean crystal grain size of 2 μm or more in the major axis direction and has a mean crystal grain size of 1 μm or less in the minor axis direction.