R&D: Effect of C Replacement on Magnetic Properties and Nanostructure of FePt-Nitride Granular Film for HAMR Media

IEEE Transactions on Magnetics has published an article written by Kim Kong Tham, Ryosuke Kushibiki, Tanaka Kikinzoku Kogyo K. K, Tsukuba, Japan, and Shin Saito, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.

Abstract: “The effect of adding carbon (C) grain boundary material (GBM) on magnetic properties and nanostructure of FePt-nitride granular films with various nitrides is reported. Saturation magnetization of FePt-nitride-C granular films shows similar tendency with that of FePt-nitride granular films which varies almost linearly against volume averaged melting point ( T _m ^ave ) of the GBM. The values of perpendicular magnetic anisotropy and degree of order of L1 ₀ -FePt phase for all FePt-nitride granular films are enhanced and the amount of magnetic grains with c -axis parallel to the film plane is reduced when nitride is partially replaced with C. Furthermore, by replacing nitride with C, the grain to grain separation is promoted significantly. When T _m ^ave of the GBM increases from around 2500 to 3500°C, in general, the average cluster diameter ( CD ) and cluster boundary decreases from around 13 to 9 nm and from 12 to 5 nm, respectively. Considering of T _m ^ave of the GBM, these results suggest that the GBM with high T _m ^ave will solidify prior to FePt which acts as the nucleation site to reduce the CD , which is similar to CoPt-based alloy granular films.“