The coupling effect between ferroelectric and frustrated antiferromagnetic ordering in hexagonal ferroelectromagnet

Effects of the magnetoelectric coupling between the frustrated antiferromagnetic and ferroelectric ordering in hexagonal ferroelectromagnet are investigated by the soft-mode theory and molecular-field approximation. Applying the Heisenberg model for frustrated triangular antiferromagnets with exchange anisotropy and Diffour model for ferroelectric interaction, we discuss thermodynamic properties of the hexagonal ferroelectromagnetic system, including mean magnetization 〈si〉, polarization p, magnetization susceptibility χm, and polarization susceptibility χp, in a possible coupling form related to a combination of electric polarization and spin correlation. It is found that polarization induced by magnetic coupling leads to an anomaly in χp and a cusp in χm at low-temperature, which is consistent qualitatively with experimental results in hexagonal ferroelectromagnet YMnO3.