Patent ID: 7901803

Claim:
A perpendicular magnetic recording medium comprising: a substrate; at least one underlayer formed above the substrate; and a perpendicular magnetic recording layer formed above the at least one underlayer, an easy magnetization axis of the perpendicular magnetic recording layer being oriented perpendicular to the substrate, the at least one underlayer has a granular structure including metal particles and grain boundaries surrounding the metal particles and the perpendicular magnetic recording layer including magnetic crystal particles and grain boundaries surrounding the magnetic crystal particles, wherein the granular underlayer contains Ru as the metal particles and the grain boundaries of the metal particles contain silicon oxide and an oxide of at least one element selected from the group consisting of Li, Na, K, Rb and Cs the magnetic crystal particles contain Co as the main component and further contain Pt and Cr and the grain boundaries contain an oxide of silicon and an oxide of at least one element selected from the group consisting of Li, Na, K, Rb, and Cs, and the total amount of silicon oxide and at least one oxide of Li, Na, K, Rb, and Cs in the granular underlayer is no less than 1 mol% and no more than 20 mol% wherein a ratio of total amount of one oxide of Li, Na, K, Rb, and Cs contained at the grain boundaries in the perpendicular magnetic recording layer is no less than 1 mol% and no more than 30 mol% based on the total moles of the oxides of silicon and Li, Na, K, Rb, and Cs contained at the grain boundaries.