Internal magnetic field effect onmagnetoelectricity in orthorhombicRMnO3 crystals

We have investigated the role of the 4f moment on the magnetoelectric (ME) effect of orthorhombic RMnO3 (R=rare earth ions). In order to clarify the role of the 4f moment, we prepared three samples: (Eu,Y)MnO3 without the 4f moment, TbMnO3 with the anisotropic 4f moment, and (Gd,Y)MnO3 with the isotropic 4f moment. The ferroelectric behaviors of these samples are different from each other in a zero magnetic field. (Eu,Y)MnO3 and (Gd,Y)MnO3 show the ferroelectric polarization along the a axis in the ground state, while TbMnO3 shows it along the c axis. Such difference may arise from the influence of the anisotropic Tb 3+ 4f moment. The direction of the ferroelectric polarization of RMnO3 is determined by the internal magnetic field arising from the 4f moment. c © 2008 Elsevier B.V. All rights reserved. PACS: 75.80.+q; 71.45.Gm; 77.84.Bw; 77.80.Fm; 75.30.-m; 75.50.Ee;