Patent ID: 8895163

Claim:
A perpendicular magnetic recording medium comprising: a substrate; over said substrate, a magnetic recording layer for recording a signal, an auxiliary recording layer provided above said magnetic recording layer and having a magnetic interaction with said magnetic recording layer, a separation layer comprising Ru or an Ru compound, a multi-layer underlayer comprising Ru or a Ru compound and provided below said magnetic recording layer, said underlayer having a first underlayer on a lower layer side and a second underlayer on an upper layer side just under the magnetic recording layer, grains of said second underlayer being coarser than grains of said first underlayer, a multi-layer pre-underlayer made of a nonmagnetic crystalline material for controlling a crystal orientation of said underlayer, and a soft magnetic layer provided below said pre-underlayer, wherein when a difference between a highest point and a lowest point of unevenness of an interface between said soft magnetic layer and said multi-layer pre-underlayer, derived by a cross-sectional TEM image, is given as an interface roughness (nm) and a distance between said soft magnetic layer and said magnetic recording layer, excluding said soft magnetic layer and said magnetic recording layer, is given as a SUL-MAG distance (nm), said interface roughness (nm)<0.4(nm) and said interface roughness (nm)×said SUL-MAG distance (nm)<12(nm) are satisfied, wherein said separation layer comprises WO 3 .