Magnetization switching in multiferroic ceramics by oxygen vacancies

This paper details investigations in two multiferroic materials, Co-doped BaTiO ₃ (BTO) and pure BiFeO ₃ (BFO). The Co doping in BTO was to induce a magnetic moment into the ferroelectric BTO crystal while BFO is known to be ferroelectric and magnetic. Co-BTO was synthesized and studied in the bulk ceramic form while BFO was sputter deposited onto a Si substrate and studied in the thin film form. The samples were heated in argon and air at specified temperatures and their magnetic properties were assessed. It was found that heating in O-poor, argon induced a significantly higher magnetic moment at saturation while the O-rich atmosphere did not. Subsequent investigations using XANES and XPS seem to indicate that the O-vacancy levels changed when heated in these atmospheres. Repeated heating in the two atmospheres, alternatively, confirmed the magnetic switching. Hence, the saturation magnetization in this material could be manipulated by prior heat treatment. This could also be a material to sense the O-level in a high temperature gaseous environment since it would be registered in its memory as the magnetic saturation moment.