Abstract
Two methods using torque measurement in magnetic fields of up to 90 kOe were applied to evaluating the magnetocrystalline anisotropy of FePt nanoparticle samples with various order parameters. The maximum anisotropy field in the samples was obtained from the rotational hysteresis loss measurement. It was shown that the maximum anisotropy field monotonically increases with the order parameter. The magnetic anisotropy constant corresponding to the maximum anisotropy field of the sample with an order parameter of 0.96 is 4.4×107erg/cm3. The anisotropy field distribution was also obtained by using Flanders and Shtrikman's method. Thermal relaxation of magnetization was, however, superimposed on the anisotropy field distribution at 300 K.
