Competition between ferromagnetic and antiferromagnetic ground states in multiferroic BiMnO3 at high pressures

The crystal and magnetic structures of BiMnO3 were studied at high pressures up to 10 GPa by means of neutron diffraction in the temperature range 2-300 K. Three structural modifications, two monoclinic and one orthorhombic were found to exist in the pressure range studied and their structural parameters were determined. A suppression of the initial ferromagnetic state and formation of a new antiferromagnetic state with a propagation vector (1/2 1/2 1/2) was observed at P similar to 1 GPa, accompanied with the monoclinic-monoclinic structural transformation. Possible mechanisms of the pressure-induced magnetic transition and origin of magnetoelectric phenomena in BiMnO3 are discussed.