Advanced granular-type perpendicular recording media

We introduce our recent experimental results for three blocked layers for currently used perpendicular recording media; a recording layer (RL: for recording), a soft magnetic underlayer (SUL: magnetic flux path in writing), and a nonmagnetic intermediate layer (NMIL: underlayer of RL and separation layer between RL and SUL). For the NMIL, uniaxial crystallographic symmetry is an essential requirement for suppression of variant growth of magnetic grains in granular-type RL. From this view point, AlN with wurtzite structure and materials with pseudo-hcp structure, which means fcc structure with stacking faults, were found to be effective. For the SUL, disordered hcp CoIr with negative Ku were found to well suppress both spike noise and track erasure due to a wide distribution of magnetic flux under the return yoke in writing and formation of a Neel wall instead of a Bloch wall in the SUL. For the RL, positive-/negative-Ku stacked media with incoherent switching mode was found to be effective in order to solve the recent write-ability problem for high Ku RL material with high thermal stability. Applying all these items, an advanced medium concept with the stacking structure of “CoPtCr-oxide/CoIr-oxide/CoIr/pseudo-hcp nonmagnetic layer/substrate” is very promising from the view point of (1) switching field reduction of a RL with high Ku material, (2) conventional amorphous SUL free, and (3) conventional NMIL free.