Temperature Dependence and Microstructure Effects on Magnetic Properties of FePt(B, Ag, C) Film

A FePt(B, Ag, C) granular film was formed from post-annealed B₄C(1.0 nm)/FePt(Ag, C) layers at a substrate temperature of 470 °C for 2 min. The 6 nm thick FePt(B, Ag, C) film demonstrates high perpendicular magnetic anisotropy (K_u = 2.83 × 10⁷ erg/cm³ at 100 K) and out-of-plane coercivity (H_c = 38.0 kOe at 100 K). The K_u and out-of-plane H_c are respectively increased from 38% and 46% between 350 K and 50 K. The sample with a thickness of 8 nm also shows a similar trend for magnetic properties; however, the tiny magnetization kink which may come from rare Fe-B or disordered FePt grains was observed in the easy axis loop. The intrinsic (ΔH_int = 12.6 kOe) and extrinsic switching field distribution (ΔH_ext = 1.62 kOe) were characterized by major and minor loops to correlate the microstructural grains. The coupled FePt grains grown on a single MgTiON grain were observed in a high-resolution transmission electron microstructure (HRTEM) image. This small intergranular exchange coupling was defined by estimating the magnetic cluster size (46.6 nm) from ΔH_ext and the average grains size (28.2 nm) from TEM images. The temperature dependence of coercivity was fitted to further understand the magnetization reversal process. The lower microstructural parameter was evidenced in the imperfect grain morphology.