Preparation of exchange coupled CoFe2O4/CoFe2 nanopowders

The CoFe2O4 cobalt ferrite nanoparticles were synthesized by the hydrothermal method. At the reaction temperature of 200 degrees C, the particle sizes were controlled in the range of 22-41 nm by varying the reaction time t(r) from 2.0 to 15 h and the spontaneous magnetization M-s of samples was increased from 68.6 to 78.2 Am-2/kg. The X-ray diffraction diagrams of obtained samples showed their pure ferrite spinel structure. The highest coercivity H-c value of 184.5 kA/m was achieved by t(r) = 8 h (denoted by CFO). The sample was synthesized with a time reaction of 2 h which was reduced to form CoFe2 (denoted by CF) nanoparticles by H-2 flow 300 mL/min at 380 degrees C. The CFO/CF powders were milled by the high energy mechanical ball milling in a SPEX 8000. After milling for 2 h, the M-s and H-c values of the CFO/CF nanocomposite powders with 10 wt% CoFe2 nanoparticles fraction were 81.5 Am-2/kg and 192.4 kA/m, respectively. The microstructure and magnetic properties of all samples are discussed in detail.