Magnetic properties and microstructure of FePt (Ag, C) films with MgTiOBN/CrRu underlayer

Abstract

The (001) textured L10 FePt film is the promising candidate material for coming heat assisted magnetic recording technology. The material of epitaxial intermediate layer for FePt based granular film was considered by the surface energy and lattice mismatch between FePt and MgO-based materials. The (00L) textured FePt (Ag, C)/MgTiOBN/CrRu film was prepared and the MgTiOBN intermediate layer was prior explored in this study. This layer was sputtered by MgTiOBN target at 435 °C and formed the (002) texture on CrRu (002)/glass. The 6–12 nm thick FePt films were finally deposited on MgTiOBN at 470 °C. The FePt (Ag, C) films illustrate high perpendicular magneto- crystalline anisotropy (Ku) (3.85–3.97 × 107 erg/cm3) and out-of-plane coercivity (17.3–20.1 kOe). The lower in-plane magnetization is evidenced by the lower remanence ratio, [Mr(in-plane)/Mr(out-of-plane) ~0.08–0.14]. The saturation magnetization (Ms) of FePt films are around 752–775 emu/cm3 after co-sputtering with 40 vol% (Ag, C) segregants. From cross-sectional transmission electron microscopy image, the FePt shows island-like grains with contact angle between 35 and 67° and the average FePt grains size is around 20 nm estimated from plane view microstructural images. The reason for nonuniform trapezoidal islands is that diffusive C can penetrate and separated the FePt grains but agglomerated again during thin film formation and the lower grains contact angles was due to close surface energy between MgTiOBN and FePt layer. The release of lattice strain energy was formed the misfit dislocation in between FePt/MgTiOBN interface and epitaxial domain match was evidenced in the (111) plane system.