	US 7,601,445 B2
	Perpendicular magnetic recording medium and magnetic recording/reproducing apparatus
Takeshi Iwasaki, Yokohama (Japan); Soichi Oikawa, Tokyo (Japan); Futoshi Nakamura, Ichikawa (Japan); Tomoyuki Maeda, Kawasaki (Japan); Hiroshi Sakai, Ichihara (Japan); Akira Sakawaki, Ichihara (Japan); and Kenji Shimizu, Chiba (Japan)
Assigned to Showa Denko K.K., Tokyo (Japan); and Kabushiki Kaisha Toshiba, Tokyo (Japan)
Appl. No. 10/572,780 PCT Filed Sep. 22, 2004, PCT No. PCT/JP2004/014300 § 371(c)(1), (2), (4) Date Mar. 21, 2006, PCT Pub. No. WO2005/031713, PCT Pub. Date Apr. 07, 2005.
Claims priority of provisional application 60/507124, filed on Oct. 01, 2003.
Claims priority of application No. 2003-333480 (JP), filed on Sep. 25, 2003.
Prior Publication US 2007/0042227 A1, Feb. 22, 2007
Int. Cl. G11B 5/65 (2006.01)

U.S. Cl. 428—836.2 [428/800; 428/826; 428/836]

11 Claims

1. A perpendicular magnetic recording medium comprising at least

a nonmagnetic under layer,

a magnetic layer, and

a protective layer stacked on a nonmagnetic substrate, wherein

said magnetic layer includes a ferromagnetic crystal grain and a nonmagnetic grain boundary region;

said magnetic layer comprises a total of 0.1 to 30 mol % of oxides which form said crystal grain boundary region;

said oxides which form said crystal grain boundary region comprises:

at least one oxide selected from group A of Y oxides, W oxides, Mg oxides, Al oxides, Zr oxides, and Hf oxides; and

at least one oxide selected from group B of Ti oxides, Ce oxides, Si oxides, Cr oxides, Ni oxides, and Ta oxides; and

the content of the oxide selected from the group A in mole percentage is smaller than the content of the oxide selected from the group B in mole percentage in the oxides which form said crystal grain boundary region.