R&D: Evaluation of Blocking Temperature and Distribution for L10-type FePt Granular Films

Japanese Journal of Applied Physics has published an article written by Daiki Isurugi, Takashi Saito, Shun Kaneko, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan, Kim Kong Tham, Tanaka Kikinzoku Kogyo K. K., Tsukuba 300-4247, Japan, Tomoyuki Ogawa, and Shin Saito, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan.

Abstract: “The blocking temperature (T_B) and blocking temperature distribution (ΔT_B) of magnetic grains were evaluated for L1₀-type FePt granular films with various grain boundary materials (GBMs). T_B and ΔT_B were measured from remanent magnetization. The relationship between the degree of order and Curie temperature (T_C) for the L1₀-type FePt phase was separately evaluated using alloy films. According to actual measurements, the obtained mean T_B, mean T_B/T_C and ΔT_B for granular films were 620 K, 0.83 K, and 200 K, respectively, for SnO GBM film and 450 K, 0.61 K, and 260 K, respectively, for TiO₂ GBM film. Based on these values, mean T_B, mean T_B/T_C, and ΔT_B were calculated assuming that τ = 2 × 10⁻⁷ s, which is the relaxation time, corresponds to the HAMR writing time. These were 737 K, 0.98 K, and 24 K, respectively, for SnO GBM film and 685 K, 0.93 K, and 72 K, respectively, for TiO₂ GBM film. These results for granular films can be useful for designing a hard disk drive with HAMR.“