Role of t2g electrons in Mn-Tb coupling of multiferroic TbMnO3

We investigate the effect of Cr-doping in polycrystalline TbMn1−xCrxO3 (x ≤ 6%) ceramics on the magnetism, ferroelectricity, and dielectricity. The Cr substitution gradually suppresses the ferroelectricity induced by the Mn spiral spin ordering, and results in a stronger modulation of polarization by magnetic field with increasing x. However, the transition temperature TTb corresponding to onset of Tb magnetic ordering has barely shifted with Cr doping. In other words, although the Cr-doping obviously disrupts the Mn spiral spin ordering, the exchange field JMn-Tb acting on the Tb moments from the Mn-spin structure is hardly impacted. Our work demonstrates that the eg electron of Mn3+ plays an important role in forming the Mn spiral spin order, but the f-d exchange interaction between the Mn 3d spins and the Tb 4f moments in multiferroic TbMnO3 almost involves only the t2g electrons