Surface modification of FePt(Ag, C) granular film by ultrathin B4C capping layer

Abstract

The in-plane magnetic component in FePt-40 vol% (Ag, C) granular film was caused by lower ordering degree which lower the magnetic anisotropy field and out-of-plane coercivity (Hc = 23.6 kOe). To inhibit the FePt grains with second nucleation, random texture and in plane c-axis, the ultrathin B4C layer with thickness of 1 nm was capped. After surface modification, the FePt-40 vol% (Ag, C) film illustrates high perpendicular magnetic anisotropy (Ku = 1.75 × 107 erg/cm3) and out-of-plane coercivity (Hc = 28.8 kOe). The in-plane remanence magnetic moment is small and the tiny magnetization kink at zero field was not observed in easy-axis loop of 6 nm thick FePt-40 vol% (Ag, C) film. The ordering degree and the average surface roughness of FePt-(Ag, C) films were improved by surface diffusion of B4C which deposited at 470 °C and post-annealed for 2 min. Further, the perpendicular magnetic anisotropy and out-of-plane coercivity of FePt-(Ag, C) films were enhanced significantly. The TiOx are more favorable than TiN in MgTiON layer due to formation enthalpy, part of N atoms was diffused and incorporated in the FePt lattice evidenced in high angle angular dark field mapping. After post annealing, the released N atoms cause lots of vacancies and defects inside FePt film which promote the ordering degree.