The magnetic phase transition in ordered and disordered ferrimagnets

The magnetic phase transition is investigated for the homogeneous ferrimagnet Fe 3O 4 and the structurally disordered ferrites Zn x Ni 1− x Fe 2O 4 with x=0, 0.25, 0.5 and 0.75. No influence of structural disorder on the asymptotic critical exponents, but a strong effect on the thermodynamic behavior beyond the asymptotic critical regime was obtained. As in the case of ferromagnets, the effective Kouvel-Fisher exponent γ( T) first increases with increasing temperature for the disordered systems, whereas it initially decreases for the homogeneous ferrimagnet.