Enhancement of ferroelectric and magnetic properties in BiFeO₃ films by small amount of cobalt addition

Both the ferroelectric and magnetic properties of polycrystalline BiFe O3 films fabricated by chemical solution deposition were enhanced by adding small amounts of cobalt. Addition of 3 at. % cobalt to BiFe O3 films increased the remanent polarization from 49 to 72 μC cm2 and decreased the electric coercive field from 0.54 to 0.44 MVcm. The ferroelectricity degraded when the cobalt concentration exceeded 9 at. % due to the formation of the secondary phases of Bi2 Pt. The saturation magnetization was drastically enhanced by the addition of cobalt up to 12 at. %. This is because the magnetic moments are not canceled locally since the differences of magnetic moment between B -sites. The saturation magnetization decreased when the cobalt content exceeded 15 at. %, thereby attributing to the formation of a nonmagnetic secondary phase of Bi2 Pt. It is concluded that both ferroelectric and magnetic properties were enhanced, provided only small amount of cobalt were added to the films.