Controlling the magnetic properties of CoCrPt thin films by means of thin hexagonal-close-packed intermediate layers

Abstract

CoCrPt films for longitudinal recording media were investigated as a function of substrate bias applied during the deposition. CoCrPt films were deposited on an underlayer stack consisting of glass/NiAl/CrMn with bias applied only during deposition of the CoCrPt layer. A strong dependence of the CoCrPt coercivity on the substrate bias was observed when a thin hexagonal-close-packed CoCrTa template was added as an intermediate layer between the CoCrPt and NiAl/CrMn underlayers. This effect was not observed in the absence of the CoCrTa layer. Microstructural investigation of CoCrPt thin films using grazing incidence and conventional x-ray diffraction indicated that the lattice of the CoCrPt increased in both the in-plane and normal directions as the bias was increased. A compositional analysis from both inductively coupled plasma and energy dispersive x-ray fluorescence measurements revealed that negative substrate bias applied during CoCrPt deposition changed the Pt content from 12 to 37 at. % in the CoCrPt films. The compositional change greatly improved the coercivity of the cobalt films up to 4300 Oe. At these large Pt concentrations, the CoCrTa intermediate layer was needed to reduce the lattice mismatch between the CoCrPt magnetic layer and NiAl/CrMn underlayers. This resulted in suppression of the Co (00.2) out-of-plane texture, and allowed high coercivity to be achieved.