Role of vacancies in transport and magnetic properties of nickel ferrite thin films

Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the monotonic increase in saturation magnetization and the non-monotonic increase in electrical conductivity depend on the oxygen partial pressure during the growth of the thin films. A substantial reduction in magnetization was found which ranged between 0.4% and 40% of the bulk value as the oxygen partial pressure increased from 0.2 x 10(-6) Torr to 500 mTorr during the deposition of the films. There was a three orders of magnitude increase in conductivity for the sample prepared under the most oxygen deficient environment ( partial pressure of oxygen 0.2 x 10-6 Torr). These variations in saturation magnetization and conductivity are described within the framework of cation/oxygen vacancies in an inverse spinel nickel ferrite structure. The changes in the electronic structure due to the presence of the vacancies were investigated using x-ray photoelectron spectroscopy, which confirmed the formation of lower valent Ni for the samples prepared in an oxygen deficient atmosphere.