Synthesis and properties of Ni-Zn ferrite thin films

We have investigated the magnetic and structural properties of polycrystalline Ni-Zn ferrite thin films with thicknesses of about 1000Å. The films were prepared by R F sputtering deposition in 1.5x10-3 mbar argon atmosphere, using targets with nominal composition Ni0.7Zn0.3Fe2O4. The effects of substrate temperature and post deposition heat treatment of thin films were examined. The X-ray spectra of Fe-Ni-Zn oxides deposits reveal the formation of spinel phase of Ni-Zn ferrite, that is characteristic for these materials, only for temperatures higher than 500°C. TEM and ED indicate that the initially amorphous thin films, deposited at 100°C, become polycrystalline by heat treatment. The grain size of the crystallites is 800Å to 1000Å for Ni-Zn ferrite thin films annealed at 900°C. V.S.M. measurements show coercive fields of 12 kA/m for thin films annealed at 900°C, which are larger than those found for Ni-Zn ferrite targets. This value of coercive field is related to the shape anisotropy originated by the film microstructure and with the increase in the number of low angle grain boundaries, which act as pinning sites for domain walls. Saturation magnetization values of 220-250mT for Ni-Zn ferrite thin films are higher than half of bulk values