Structure and Magnetic Phase Diagrams of Multiferroic Mn2GeO4

Crystallographic structure and magnetic phase diagrams were investigated for single crystals of multiferroic Mn2GeO4 showing successive magnetic transitions at T-N1 = 47 K, T-N2 = 17 K, and T-N3 5.5 K. Substantial anomalies of lattice distortion were observed at the respective magnetic transition temperatures. We also found that the phase boundary at T-N2 remarkably shifts by applying a magnetic field H and strongly depends on the direction of H. Possible origins of the observed phenomena are discussed from the perspective of magnetic interactions and relevant magnetostriction in Mn2GeO4 with the olivine structure.