Magnetic properties of nanophase CoFe2O4 particles

Fine CoFe2O4 particles with average size of 50 Angstrom have been produced by coprecipitation from Fe(II) and Co(ll) solutions followed by a low-temperature calcination. The ac and de magnetic susceptibilities, as well as magnetization, were studied between 5 and 300 K. The disordered system of such particles behaves superparamagnetically above T-B = 250 K and ferrimagnetically below this temperature. T-B can be considered as mean blocking temperature at zero field in the timescale of ac (111.1 Hz) magnetic susceptibility measurements, The anisotropy field exceeds 50 kOe below 150 K. The maximal coercivity measured at 5 K is 14.5 kOe and the maximal measured magnetization is 14.6 emu/g, which is much lower than the saturation magnetization of bulk CoFe2O4.