Magnetic, dielectric, and magnetoelectric properties in Sr2CoGe2O7

We investigate the magnetoelectric effect in Sr₂CoGe₂O₇, which has a two-dimensional magnetic interaction between Co ions in the ab plane. This compound shows a weak magnetism and field-induced magnetic transition below the temperature of 7 K. It does not exhibit electric polarization under zero magnetic field. However, by applying an external magnetic field, the electric polarization is induced around its Néel temperature and increases with increasing magnetic field. The induced electric polarization in Sr₂CoGe₂O₇ is almost two orders of magnitude smaller than that of Ba₂CoGe₂O₇. This result suggests that the different ionic radius of the strontium and the barium anion plays a key role in determining the property of electric polarization. The origins of electric polarization and magnetoelectric effect are discussed.