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 oC. 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.