Abstract
Nanocrystalline (Ni0·5Zn0·5)xCo1−xFe2O4 with 0⩽x⩽1·0 are prepared by spraying co-precipitation method. Their microstructure and magnetic properties are investigated. The results show that nanocrystalline (Ni0·5Zn0·5)xCo1−xFe2O4 ferrites are spinel phase. Coercivity and retentivity of specimens increase with cobalt content. The enhancement of the saturation magnetisation up to a maximum value of 102·1 A m2 kg−1 in nanocrystalline (Ni0·5Zn0·5)0·5Co0·5Fe2O4 ferrite is observed. This can be attributed to the change of the net magnetic moment between the sublattices of structure for the substitution of Ni2+ and Zn2+ ions with Co2+ ions. The coercivity of nanocrystalline (Ni0·5Zn0·5)0·5Co0·5Fe2O4 ferrite increases monotonously in the grain size regime d<69 nm, and then coercivity decreases with grain size. The initial increase in coercivity of the nanocrystalline (Ni0·5Zn0·5)0·5Co0·5Fe2O4 ferrite with increasing size is due to the enhanced role of the surface and its strong random anisotropy.
This work was supported by National Nature Science Foundation of China (51174006), the Natural Science Foundation of High Education School of Anhui Province, China (No: KJ2010A095), Anhui Provincial Natural Science Foundation, China (1208085ME84) and The Project-sponsored by SRF for ROCS, SEM.