Magnetic behaviour of nanocrystalline Ni0.5Cu0.5Fe2O4 spinel ferrite

The magnetic behaviour of the nanocrystalline Ni0.5Cu0.5Fe2O4, synthesized by the co-precipitation method has been studied. The X-ray diffraction patterns confirm the formation of cubic spinel structure. The dc magnetization measurements show that the samples are superparamagnetic above the blocking temperatures and the blocking temperature increases with particle size. The reduction in saturation magnetization in the case of nanoparticles as compared to their bulk counterpart has been explained on the basis that the magnetic moments in the surface layers of a nanoparticle are in a state of frozen disorder. The hump in ZFC curve progressively shift to a lower temperature with increasing field and broader curves at higher field, suggests the spin-glass nature of the system.