Magnetic properties and microstructure of FePt (BN/AlN, Ag, C) film

The FePt (BN/AlN, Ag, C) and reference FePt (BN, Ag, C) films exhibit close ordering degrees (0.84), indicating that the hard L1₀ FePt phase is nearly identical in both films. The reference FePt (BN, Ag, C) film presents perpendicular magnetic anisotropy and the highest out-of-plane coercivity (31.7 kOe). Still, the disordered fcc FePt contributed to the in-plane magnetization and wider hard-axis hysteresis loop. In contrast, the FePt (BN/AlN, Ag, C) film exhibits higher c-axis alignment, as evidenced by lower rocking width in the (001) / (002) diffraction peaks (3.94 °/2.5 °). The more c-axis anisotropic crystal grains also respond to the higher magneto-crystalline anisotropy, and lower hard-/easy-axis remanence ratio than the reference sample. However, the out-of-plane coercivity is significantly smaller in the FePt (BN/AlN, Ag, C) film (16.7 kOe) due to the formation of soft magnetic FeB grains, where the hard- and soft-magnetic phases are exchange-coupled, which enhances the magnetic remanence and saturation magnetization. From microstructure image mapping, AlN segregated at the grain boundaries, but part of Al was present in the FePt lattice and was supposed to initiate the formation of FeB due to high atomic diffusivity at high deposition temperature.