Patent ID: 7524570

Claim:
A perpendicular magnetic recording medium comprising: a substrate; a perpendicular magnetic recording layer; and an underlayer comprising magnetically permeable material between the substrate and the recording layer, the magnetically permeable material being an alloy consisting essentially only of Co, Fe, Ta and Zr wherein the combined amount of Ta and Zr in said CoFeTaZr alloy is greater than or equal to 10 atomic percent and less than or equal to 20 atomic percent and the moment (M s ) is greater than or equal to 11 kOe, and wherein said CoFeTaZr alloy exhibits a corrosion current at zero electrical potential in an electrochemical corrosion test and a Co 92 Ta 3 Zr 5 alloy exhibits a corrosion current at zero electrical potential in said test that is at least 15 times the corrosion current of said CoFeTaZr alloy.