Raman effect and magnetic properties of doped TbMnO3

The room temperature Raman scattering, structural and temperature variation of magnetic properties of Y- and Ni-doped TbMnO3 are investigated. Both for Y and Ni doping, the Neel temperature (T-N) decreases. Y doping reduces effectively both the J(Tb-Tb) and J(Mn-Mn) exchange interactions, whereas Ni doping on the Mn site decreases only the J(Mn-Mn) exchange interaction. The reduction in TN in the Ni-doped sample cannot be explained with simple exchange integral. It might be the case that Ni2+ doping changes the polarization flop observed in TbMnO3 which in effect may change the exchange interaction. In the room temperature Raman spectra for TbMnO3 and Y-doped TbMnO3 eight modes are observed. When Ni is doped, modes due to MnO6 bending and in-plane O-2 stretching broaden and few modes disappear due to the induced lattice disorder.