Microstructure and magnetic properties of nanocrystalline (Ni_0·5Zn_0·5)_xCo_1−xFe₂O₄ ferrite by spraying co-precipitation method

Abstract

Nanocrystalline (Ni_0·5Zn_0·5)_xCo_1−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 (Ni_0·5Zn_0·5)_xCo_1−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 (Ni_0·5Zn_0·5)_0·5Co_0·5Fe₂O₄ 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 (Ni_0·5Zn_0·5)_0·5Co_0·5Fe₂O₄ 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 (Ni_0·5Zn_0·5)_0·5Co_0·5Fe₂O₄ ferrite with increasing size is due to the enhanced role of the surface and its strong random anisotropy.

Keywords:

• Nanocrystalline materials
• (Ni_0·5Zn_0·5)_xCo_1−xFe₂O₄ ferrite
• Microstructure
• Magnetic properties

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.