Annealing induced structural change in sputter deposited copper ferrite thin films and its impact on magnetic properties

Copper ferrite (CuFe2O4) thin films have been prepared by rf sputtering on fused quartz and silicon (111) substrates at ambient temperature. The as-deposited film is found to be in cubic phase, which is stable only at higher temperatures in bulk. The films were annealed at temperatures ranging from 100 degreesC to 800 degreesC and slowly cooled. The films had tetragonal structure at annealing temperature above 200 degreesC. The c/a ratio was observed to increase with increasing annealing temperature. Transmission electron microscopy study confirmed the phase transformation from cubic to tetragonal as a function of annealing temperature. The magnetization values of the films were observed to show a maximum at the annealing temperature of 200 degreesC and a minimum at 500 degreesC. The coercivity increased monotonically from 70 Oe for the as-deposited film, to 1450 Oe for the film annealed at 800 degreesC. The results were explained on the basis of the phase transformation and the grain growth phenomenon.(C) 2002 American Institute of Physics.