Microstructure and magnetic properties of nanocrystalline (Ni _0·5Zn _0·5) _xCo ₁₂xFe ₂O ₄ ferrite by spraying co-precipitation method

Nanocrystalline (Ni _0·5Zn _0·5) _xCo ₁₂xFe ₂O ₄ with 0(x(1·0 are prepared by spraying co-precipitation method. Their microstructure and magnetic properties are investigated. The results show that nanocrystalline (Ni _0·5Zn _0·5) _xCo ₁₂xFe ₂O ₄ 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 kg21 in nanocrystalline (Ni _0·5Zn _0·5)0·5Co0·5Fe ₂O ₄ ferrite is observed. This can be attributed to the change of the net magnetic moment between the sublattices of structure for the substitution of Ni ²⁺ and Zn ²⁺ ions with Co2z ions. The coercivity of nanocrystalline (Ni _0·5Zn _0·5) 0·5Co0·5Fe ₂O ₄ 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 (Ni _0·5Zn _0·5)0·5Co0·5Fe ₂O ₄ ferrite with increasing size is due to the enhanced role of the surface and its strong random anisotropy.