Dependence of sputtering power and soft underlayer on magnetic properties in CoCrPtO perpendicular recording media

In this paper, sputtering power dependence on magnetic properties and microstructure of CoCrPtO perpendicular recording media was examined. Also, change of magnetic properties of CoCrPtO layers on two different soft underlayers was investigated. As the oxygen gas ratio increases, coercivity (Hc) increases regardless of the variation of the sputtering power up to a certain critical oxygen gas ratio which depends on the sputtering power. Then, Hc drops sharply in all cases. The higher the power is, the higher the critical oxygen gas ratio is. As the oxygen gas ratio increases, exchange slope also decreases more rapidly at the lower sputtering power than higher power. The small grains of the size of ∼7 nm with thick amorphous-like grain boundaries are observed in the media sputtered at the power of 75 W. It is considered that the selective oxidation of grain boundary is performed more effectively at low sputtering power. CoCrPtO layer on NiFeNb soft magnetic underlayer (SUL) showed higher Hc of 5000 Oe and well isolated grain in comparison with CoCrPtO layer on CoZrNb SUL. This difference of coercivity behavior may be associated with difference CoCrPtO layer on residual stress or surface roughness.