Dynamic magnetoelectric effect of the polar magnet CaBaCo₄O₇

We have investigated the temperature and magnetic field dependence of the dynamic magnetoelectric coefficient α_E of the polar magnet CaBaCo₄O₇. The temperature dependence of α_E exhibits a peak at the magnetic transition temperature T_C in zero magnetic field, evidencing an enhanced magnetoelectric effect near the phase boundary. When a DC magnetic field is applied along either a- or b-axis, the peak position of α_E shifts continuously to a higher temperature while the peak amplitude reaches the maximum at a critical field and decays for higher magnetic fields. The obtained magnetoelectric phase diagram suggests that the maximum dynamic magnetoelectric effect occurs in a region above T_C where short-range magnetic correlations play a crucial role and the peak is due to a metamagnetic transition. The measurements of the magnetostrictive coefficient dλ/dH reveal that the magnetoelectric effect is closely related to the magnetoelastic coupling. Our study provides insights toward achieving significant dynamic magnetoelectric effect at high temperatures in polar magnets.