Evaluation of blocking temperature and its distribution for L10-type FePt granular films

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.