Perpendicular magnetic recording disk with multiple magnetic layers and intermediate dual nucleation films for control of grain size

A perpendicular magnetic recording disk comprising:

• a substrate;
• an underlayer of magnetically permeable material on the substrate;
• a nonmagnetic intermediate layer (IL) on the underlayer and comprising a material selected from Ru and a Ru alloy;
• a perpendicular magnetic recording layer comprising
• a first magnetic layer (MAG1 ) comprising a granular ferromagnetic alloy comprising Co, Pt and Cr and one or more oxides of one or more of Si, Ta, Ti, Nb and B on the IL;
• a first nucleation film (NF1 ) consisting of Ru on and in contact with MAG1 and having a thickness greater than or equal to 0.1 nm and less than or equal to 1.5 nm;
• a second nucleation film (NF2 ) on and in contact with NF1 and having a thickness greater than or equal to 0.2 nm and less than or equal to 1.0 nm, wherein NF2 is a discontinuous film of clusters consisting of an oxide of Ta;
• and
• a second magnetic layer (MAG2 ) ferromagnetically exchange coupled to MAG1 across NF1 and NF2, MAG2 being formed of a granular ferromagnetic alloy comprising Co, Pt and Cr and one or more oxides of one or more of Si, Ta, Ti, Nb and B on and in contact with said clusters of NF2 and on portions of NF1 , wherein MAG2 has more Pt and less Cr than MAG1 and an anisotropy field greater than the anisotropy field of MAG1.