Perpendicular media with improved corrosion performance

1. A perpendicular magnetic recording medium comprising a chromium-free magnetic layer on a substrate and a protective overcoat or a lubricant layer on the magnetic layer, the magnetic layer comprising cobalt, platinum, and molybdenum, the magnetic layer having perpendicular magnetic anisotropy, wherein the magnetic layer comprises molybdenum at a concentration in the range of about 0.5 atomic % to about 6 atomic % and the magnetic layer has a granular structure comprising grains and a passivating structure around grains, the passivating structure comprising molybdenum and oxygen, wherein the passivating structure provides corrosion resistance by inhibiting Co or Co ion migration from the grains to the protective overcoat or the lubricant layer,

further comprising:

an intermediate layer on the substrate, the intermediate layer comprising ruthenium.

2. The perpendicular magnetic recording medium of claim 1 , wherein the magnetic layer comprises a material having the general formula CoPt x Mo z , and wherein x is between about 15 atomic % and about 25 atomic %, and z is between about 0.5 atomic % and about 6 atomic %.

3. The perpendicular magnetic recording medium of claim 1 , wherein the magnetic layer further comprises at least one of B, Ta, Nb, Si, Ni, and Ti.

4. The perpendicular magnetic recording medium of claim 1 , further comprising:

at least one underlayer on the substrate and below the magnetic layer; and the protective overcoat having a thickness of less than about 60 Å.

5. The perpendicular magnetic recording medium of claim 1 , wherein the magnetic layer consists of cobalt, platinum, molybdenum and oxygen.