Preparation of nanocrystalline CO_1-xNi_xFe₂O₄ ferrite and effect of Ni²⁺ on its magnetic properties

Nanocrystalline Co_1-xNi_xFe₂O₄ ferrite powder with 0 ≤ x ≤ 1 was prepared by the spraying-coprecipitation method. The microstructure of Co_1-xNi_xFe₂O₄ ferrite powder was characterized by thermogravimetry-differential scanning calorimetry, X-ray diffraction (XRD), transmission electron microscope and specific surface area test. The magnetic properties of Co_1-xNi_xFe₂O₄ ferrite were measured with a vibrating sample magnetometer at room temperature. The results show that uniform and fine nanocrystalline Co_1-xNi_xFe₂O₄ ferrite powders are obtained by the spraying-coprecipitation method. Nanocrystalline Co_1-xNi_xFe₂O₄ ferrite has a solid solution of the spinel structure according to the XRD patterns. The grain size of powder calcined at 600°C for 1.5 h is about 40 nm. There are few agglomerates with average sizes below 100 nm. The specific saturation magnetization and coercivity of nanocrystalline Co_1-xNi_xFe₂O₄ ferrite decrease with the increase of the content of Ni²⁺ at room temperature.