Magnetoelectric coupling in the cubic ferrimagnet Cu2OSeO3
  We have investigated the magnetoelectric coupling in the lone pair containing piezoelectric ferrimagnet Cu2OSeO3. Significant magnetocapacitance develops in the magnetically ordered state (TC = 60 K). We find critical behavior near TC and a divergence near the metamagnetic transition at 500 Oe. High-resolution X-ray and neutron powder diffraction measurements show that Cu2OSeO3 is metrically cubic down to 10 K but that the ferrimagnetic ordering reduces the symmetry to rhombohedral R3. The metric cubic lattice dimensions exclude a magnetoelectric coupling mechanism involving spontaneous lattice strain, and this is unique among magnetoelectric and multiferroic materials. 
Jan-Willem G. Bos, Claire V. Colin and Thomas T.M. Palstra