Synthesis, microstructure and magnetic properties of nanocrystalline Ni-Zn ferrite by a modified wet chemical method

Nanocrystalline Ni_1-xZn_xFe₂O₄ ferrites with 0 ≤ x ≤ 1 were prepared by spraying-coprecipitation method. The microstructure was investigated by TG-DSC, XRD, SEM, TEM and BET. Magnetic properties were measured with vibrating sample magnetometer at room temperature. The results showed that uniform and fine nanocrystalline Ni _1-xZn_xFe₂O₄ ferrites are obtained. The grain size of sample calcined at 600°C for 1.5h is about 30nm. There are a few agglomerates with average sizes below 100nm. The specific saturation magnetization, M_s, of the sample increases with increasing Zn ²⁺ concent x at room temperature, and the maximum M_s is 66.8 A·m²·kg^-1 as the Zn²⁺ content x is around 0.5mol. As calcining temperature increased from 400°C to 1050°C, the M_s of Ni_0.5Zn_0.5Fe ₂O₄ ferrite increases from 40.2 A·m ²·kg^-1 to 75.6 A·m²· kg^-1. The coercivity maximum is about 5.97 kA·^-1 as its critical grain size is about 62.0nm. The relation between coercivity and grain size for nanocrystalline Ni_0.5Zn_0.5Fe ₂O₄ ferrite may be explained based on random anisotropy theory.