THERMAL-STABILITY AND NANOSTRUCTURE OF COCRPT LONGITUDINAL RECORDING MEDIA

We report a systematic study of activation volumes and their correlati on with physical grain sizes and thermal stability in CoCrPt media fab ricated by magnetron sputtering. Different underlayers and CoCrPt laye r thicknesses were used to provide a range of lateral grain sizes, M(r )delta (product of remanence M-r and film thickness delta) values, and remanence coercivities. Two methods, namely the field-sweep-rate depe ndence of coercivity and measurements of magnetic viscosity and irreve rsible susceptibility, were used to determine the activation volumes a nd the results obtained from the two methods are in reasonable agreeme nt. For CoCrPt layer thickness from 10 nm to 27 nm, the activation vol umes of these films range from about 3x10(-18) cm(3) to 5x10(-18) cm(3 ), which indicate that these films are thermally stable. Furthermore, for most samples the activation volumes are close to the volumes of th e physical CoCrPt grains. This suggests that the magnetic grains in th ese films switch almost independently. Films with physical grain sizes small enough to approach thermal instability are also discussed.