We have undertaken a comprehensive theoretical study of the band structure, density of states, dependence of the Curie point and saturation magnetization on the size of NiFe2O4 nanoparticles prepared by the conventional ceramic method. Commercially available NiFe2O4 powder was first annealed in an oxygen environment in a furnace at 1100◦C for 3h. The X-ray diffraction pattern indicated that the sample was single-phase at this stage. The average grain size estimated by scanning electron microscopy (SEM) was in the range of 300 to 350nm. The magnetic behavior of the sample at room temperature was studied by means of a superconducting quantum interference device (SQUID). The Curie temperature of the nickel ferrite powder was measured using an LCR meter. The measurement of the Curie temperature and saturation magnetization indicated that a decrease in the grain size leads to a decrease in the Curie temperature and in the saturation magnetization. The small value of saturation magnetization was attributed to a spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core [1]. Good agreement was obtained between theory and experimental results.
