Anisotropic magnetic properties in Åkermanite Sr2MSi2O7 (M=Co, Mn) crystals

We have investigated the magnetic and the dielectric properties of åkermanite Sr 2 CoSi 2 O 7 and Sr 2 MnSi 2 O 7 single crystals. Sr 2 CoSi 2 O 7 shows a canted antiferromagnetism with a large magnetic anisotropy at temperatures below 7 K. By applying a magnetic field along the [110] direction, an electric polarization emerges along the c axis at temperatures below the magnetic transition temperature. In high magnetic fields, the saturation magnetization becomes enhanced only when the electric polarization appears. In contrast, the magnetization of Sr 2 MnSi 2 O 7 is isotropic at all temperatures, and its magnetic-field-induced electric polarization is very small. These results suggest that the electronic configuration of the transition-metal ion is of crucial importance for the appearance of electric polarization.