Systematic study of nitride matrix of FePt granular films for heat assisted magnetic recording media

Abstract

A systematic investigation of the magnetic properties and nanostructure of FePt-nitride granular films with nitride of various melting points (Tm) is reported. When Tm of nitride grain boundary materials (GBMs) is varied from 1650 to 3305 °C, the saturation magnetization (Msfilm) changes from 710 to 570 emu/cm3. The Msfilm of FePt-nitride is similar to that of FePt-oxide granular films, almost varies linearly against Tm. At almost the same Tm, FePt-nitride shows a higher Msfilm of around 70 emu/cm3 compared to that of FePt-oxide granular films. According to the torque measurement result of the saturated torque coefficient with fourfold components (L4θsat), FePt-nitride shows a smaller L4θsat than that of FePt-oxide granular films, which suggests that FePt-nitride has a smaller content of the in-plane component than that of FePt-oxide granular films. This is supported by the in-plane x-ray diffraction profile measurement, where FePt-nitride has a smaller integral intensity of (001) diffraction of the L10-FePt phase than FePt-oxide granular films. With further promotion of grain separation, nitrides are more promising GBMs than oxides due to their high Msfilm and smaller content of the in-plane component.