Influence of anisotropy on the grain size distribution derived from superparamagnetic magnetization curves

The effect of the magnetic anisotropy at temperatures above the blocking temperature of a uniaxial, randomly oriented, nanoparticulate magnetic system has been studied. If anisotropy is disregarded in fitting the magnetization curves, apparent particle-size distributions emerge from the calculations, even for monodisperse systems. Apparent mean grain size increases with temperature, with a saturation value corresponding to the actual particle size. This evolution collapses to a master curve for anisotropy energy terms up to the fourth order.