Patent ID: 7491452

Claim:
A perpendicular magnetic recording disk comprising: a substrate; an underlayer of magnetically permeable material on the substrate; a granular perpendicular magnetic recording layer consisting essentially only of Co, Pt, Cr, Ta and oxygen, wherein the amount of Ta present in the recording layer is greater than about 2 atomic percent and less than about 5 atomic percent, the recording layer having a hexagonal-close-packed (hcp) crystalline structure with the c-axis oriented substantially perpendicular to the recording layer and inter-granular material comprising oxides of Ta; an exchange-break layer between the underlayer and the recording layer for magnetically decoupling the recording layer and the underlayer, the exchange-break layer being a nonmagnetic hcp material selected from the group consisting of Ru and Ru-based alloys, the exchange-break layer having a thickness greater than 8 nm and less than 14 nm; and a seed layer between the underlayer and the exchange-break layer for encouraging the hcp growth of the exchange-break layer, the seed layer comprising an alloy of Ni and an element selected from the group consisting of Fe, V and W, the exchange-break layer being directly on and in contact with the seed layer; wherein the recording layer has a coercivity H c greater than about 5000 Oe and a nucleation field H n more negative than about −1500 Oe.