Anisotropy field distribution of partially ordered FePt nanoparticles

The anisotropy field distribution of various Fe–Pt nanoparticle samples with a partially ordered structure is investigated up to 90 kOe using the Flanders and Shtrikman’s method. The distribution of the Fe–Pt samples with a low order parameter of 0.66 or a nonequiatomic composition of Fe58Pt42 or Fe41Pt59 is broader than that of the Fe–Pt sample with an almost full order parameter of 0.96 at 5 K. The broad distribution is attributed to an inhomogeneous atomic arrangement with L10, L12, and disordered structures. The distribution measured at 300 K, on the other hand, is quite different from that at 5 K, indicating a significant thermal effect on the magnetization reversal.