Nickel ferrite nanoparicles with various grain sizes are synthesized using annealing treatment followed by ball milling of its bulk component materials.Commercially available nickel and iron oxide powders are first mixed,and then annealed at 1100℃ in an oxygen environment fuace and for 3h.The samples are then milled for different times in an SPEX mill.X-ray diffraction patte indicates that in this stage the sample is single phase.The average grain size is estimated by scanning electron microscopy(SEM)and x-ray diffraction techniques.Magnetic behavior of the sample at room temperature is studied using a superconducting quantum interference device(SQUID).The Curie temperature of the powders is measured by an LCR meter unit.The x-ray diffraction pattes clearly indicate that increasing the milling time leads to a decrease in the grain size and consequently leads to a decrease in the saturation magnetization as well as the Curie temperatures.This result is attributed to the spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core.