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The crystal and magnetic structures of BiMnO 3 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 1/2͒ was observed at P ϳ 1 GPa, accompanied with the monoclinic-monoclinic structural transformation. Possible mechanisms of the pressure-induced magnetic transition and origin of magnetoelectric phenomena in BiMnO 3 are discussed.

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The layered cobaltites La 2−x Sr x CoO 4 have been complexly studied over the range of mixed Co 3+/4+ valency and their properties discussed in comparison with cubic perovskites La 1−x Sr x CoO 3 . The sample x = 1.0 exhibits a paramagnetic ground state based on the intermediate spin state of Co 3+ and undergoes a broad resistivity transition at 400-900 K, associated with diffusive changes of magnetic susceptibility and volume expansion. The Co 4+ doping in samples with x Ͼ 1 induces gradually ferromagnetism and leads to a dramatic decrease of resistivity and thermopower, though the metallicity is not achieved. The neutron diffraction on the limit composition x = 1.4 suggests that the long-range ordered ferromagnetic regions coexist with paramagnetic ones, and their amount changes little with an application of high pressures up to 4.3 GPa.