Nanocrystalline Ni0.8Zn0.2Fe2O4 films prepared by spray deposition from polyol-mediated sol: Microstructural and magnetic characterization

Nanocrystalline films were directly prepared by spray deposition of a preformed polyol-based Ni0.8Zn0.2Fe2O4 sol on a moderately heated glass substrate. The microstructural and magnetic properties of these films are investigated by X-ray diffraction, scanning electron microscopy and magnetic measurements on a Super Quanducting Interference Devices magnetometer. They are compared with those of nanoparticles precipitated from the sol, and with those of film subsequently annealed in air at 400 °C. The films and the powder exhibit superparamagnetic behaviour with a blocking temperature which increases from the powder to the as-produced film to the annealed film, in agreement with increasing stress and/or crystal size. They are ferrimagnetic at low temperature with a hysteresis feature strongly dependent on the synthesis conditions. The stresses induced in the film upon deposition undoubtedly correlate with a large grain boundaries volume which contributes to the Hc, the coercitive field, increase and Msat, the saturation magnetization, decrease.