Nano-particles of cobalt ferrite have been prepared using co-precipitation method with NaOH as precipitators.X-ray diffraction

transmission electron microscope and Raman analysis confirm the formation of single-phase cobalt ferrite nano-particles.The crystal constants are between 0.830 nm and 0.840 nm

and the grain sizes are between 9.0 nm and 65.0 nm

depending on pH values of the suspensions.Magnetic measurements show that the coercivity of CoFe2O4 nano-particles increases with the increasing of grain size

the coercivity of CoFe2O4 nano-particles of 9.0 nm and 65.0 nm are 0.283 2 T and 0.467 4 T

respectively

while the saturation magnetization shows much dependence on the distribution of Co2+ and Fe3+ surface ion.