Thin films of Co1.7Fe1.3O4 prepared by radio frequency sputtering – the first step towards their spinodal decomposition

Abstract

Pure thin films of Co_1.7Fe_1.3O₄ spinel iron cobaltites were prepared for the first time by radio frequency sputtering. Such films are made of small crystallites of about 20 to 30 nm in diameter. Because Co_1.7Fe_1.3O₄ films have a composition located in the miscibility gap of Fe₃O₄–Co₃O₄, they can be submitted to spinodal transformation below about 900 °C. This transformation was also confirmed at 600 °C by X-ray diffraction and transmission electron microscopy studies. It was demonstrated however that this spinodal transformation occurs after only a few hours at low temperature. Indeed, after annealing in air at 300 to 450 °C for a few hours, the spinodal transformation leading to two-phase spinels, one rich in iron and the other rich in cobalt, was clearly revealed by Raman spectroscopy and electrical measurements.