High M-r squareness and exchange decoupled perpendicular recording media

CoCr15Pt13 perpendicular layers with CoCr-alloy/Ti dual underlayers were an nealed and it was investigated how the dual underlayer structure influences the characteristics of the CoCrPt perpendicular layer. The Ti layer thickn ess has a remarkable influence on the Cr diffusion efficiency from the uppe r underlayer of the dual underlayer into the CoCrPt perpendicular layer. Th e Cr diffusion efficiency is improved by increasing the Ti layer thickness and the addition of Th or Pt to the upper underlayer of the dual underlayer . As a result, the magnetic properties were greatly improved. For the CoCr15Pt13(40 nm)/CoCr30Pt8Ta2(20 nm)/Ti(25 nm) media postannealed at 500 degreesC for 30 min., the coercivity and M-r squareness were 7100 Oe and 0.98 respectively. Also, the slope of the MH loop at coercivity was ne arly 1/4 pi.