Patent ID: 7431999

Claim:
A perpendicular magnetic recording medium, comprising: a nonmagnetic substrate; a first underlayer formed on the nonmagnetic substrate, mainly composed of at least two kinds selected from a group consisting of Fe 2 O 3 , Co 3 O 4 , MgO, MoO 3 , Mn 3 O 4 , SiO 2 , Al 2 O 3 , TiO 2 , and ZrO 2 , and having crystal grains growing in a columnar shape and crystal grain boundaries surrounding the crystal grains, the crystal grains mainly containing at least one kind selected from a group consisting of Fe 2 O 3 , Co 3 O 4 , MgO, MoO 3 , and Mn 3 O 4 , the crystal grain boundaries mainly containing at least one kind selected from a group consisting of SiO 2 , Al 2 O 3 , TiO 2 , and ZrO 2 ; a nonmagnetic second underlayer formed on the first underlayer and having crystal grains with one of a face-centered cubic structure and a hexagonal close-packed structure growing on the crystal grains of the first underlayer; a third underlayer formed on the second underlayer and mainly composed of at least one kind selected from a group consisting of Ru,Rh, and Re; a magnetic layer formed on the third underlayer; and a protective film formed on the magnetic layer.