Magnetic anisotropy and magnetization variation with temperature

The temperature dependence of the magnetization and magnetic anisotropy in three non-interacting ferrite nanoparticle systems are compared. The first and the second are 5 nm and 13 nm γ-Fe_2+δO₃ nanocrystals which are soft ferrimagnetic and the third is 9 nm nanocrystals of CoFe₂O₄ (cobalt ferrite) which is considered to be a hard ferrimagnet. The 13 nm maghemite and the cobalt ferrite nanocrystal samples have blocking temperatures well above 100 K where temperature effects in the magnetization and anisotropy of the particles should become significant. Magnetization curves were measured both below and above the blocking temperature of each sample and the saturation magnetization values at each temperature were obtained.