Design of zinc ferrite thin films with excess tetrahedrally coordinated Fe3+ ions and their magnetic interactions

Abstract

In the present work, zinc ferrite thin films on glass substrates were grown using radio-frequency sputtering method in oxygen environment at base pressure of 2 x 1(-6) Torr. As-grown films were annealed at 200 degrees C for 1, 3 and 5 h. X-ray diffraction study envisaged the existence of peaks corresponding to (311) and (440) planes of cubic spinel structure. Both the lattice parameter and crystallite size increased with annealing time leading to crystal perfection with annealing time. Fourier transform infrared spectroscopic study showed presence of bands corresponding to metal-oxygen vibrations in the spinel lattice. Fe K-edge extended X-ray absorption fine structure (EXAFS) measurements revealed that the tetrahedral site occupancy of Fe3+ ions are 1.2 for as-grown zinc ferrite thin film. This occupancy is 1.18, 1.12 and 1.09 for annealing times of 1, 3 and 5 h, respectively. These observations were supported by Zn K-edge EXAFS investigations. X-ray magnetic circular dichroism measurements performed for these films show negative exchange interaction among the Fe3+ ions situtated at different sites. Thus, zinc ferrite thin films having excess occupancy at tetrahedral site was successfully designed on glass substrate.