Observation of Magnetic-Field-Induced Electric Polarization in Terbium Orthoferrite

In TbFeO3 orthoferrite at temperatures below the antiferromagnetic ordering temperature for the terbium subsystem (∼3.2 K), the electric polarization Pa(Hb) induced by a magnetic field Hb along the a axis is found. Such polarization is accompanied by anomalies related to metamagnetic (for Tb) and spin-reorientation (for Fe) transitions. At low magnetic fields |H| Hcr1 ∼ 5 kOe, the Pa(Hb) dependence exhibits a strong hysteresis and has a “butterfly” shape, while in intermediate-field magnetic configurations, |Hcr1| |H| |Hcr2| ~ 18 kOe, the sign of the polarization is determined by the sign of an applied electric field, and the Pa(Hb) dependence turns out to be nonmonotonic. A qualitative explanation of the observed effects is given in the framework of a symmetry analysis of the allowed magnetoelectric interactions in the field-induced magnetic structures.