Off-diagonal magnetoelectric susceptibility in single crystal Cr2O3

Previous studies of magnetoelectric effect in Cr2O3employed collinear electric and magnetic fields along the rhombohedral c axis or perpendicular to it. They determined the diagonal elements of the rhombohedral magnetoelectric susceptibility tensor, i.e., α33and α11, respectively. This study applied orthogonaI electric and magnetic fields and determined for the first time the off-diagonal element α12by the measurement of the dielectric constant. Changes in the dielectric constant of Cr2O3were studied as a function of applied magnetic field. This relationship was found to be linear. At 8 kOe, orthogonal electric and magnetic field conditions were applied from room temperature to the Néel point (307 K) at frequencies of 1, 5, and 10 kHz. Changes in dielectric constants showed two maxima within the temperature range. By the use of equations for α33and α11given by Rado, the values for α12were obtained from the dielectric constant data. The temperature plot of α12, as shown below, showed two peaks in the neighborhood of the Néel point. The α12values vanished beyond this temperature range. From the symmetry consideration, off-diagonal α12values can only exist in Cr2O3when there are antiferromagnetic domains and the inter-domain walls lower the symmetry. The two peaks of α12are additional evidence for the existence of domains in Cr2O3.