Structure and magnetic properties of Co and Ni nano-ferrites prepared by a two step direct microemulsions synthesis

Nano-particles of CoFe2O4, NiFe2O4 and Co0.5Ni0.5Fe2O4 were synthesized by a two step microemulsion precipitation where inverse micelles of water in hexanol were stabilized using cetyltrimethylammonium bromide. Powder X-ray diffraction analysis and Transmission electron microscopy measurements provided data to clarify the crystal structure and size of the produced nano-particles. Different measurements of magnetic properties at low temperatures of 2 K revealed that nano-particles of NiFe2O4 represent magnetically soft ferrite with a coercivity ∼40 kA/m, whereas nano-particles of CoFe2O4 and Co0.5Ni0.5Fe2O4 were magnetically harder with a coercivity of 815 and 947 kA/m, respectively. Additionally zero field cooling and field cooling measurements provided data for estimating the blocking temperature of the materials produced. For NiFe2O4 this temperature is lower, 23 K. The blocking temperature of CoFe2O4 of 238 K and Co0.5Ni0.5Fe2O4 of 268 K are higher in comparison with NiFe2O4.