Ga substitution as an effective variation of Mn-Tb coupling in multiferroic TbMnO3

Ga for Mn substitution in multiferroic TbMnO3 has been performed in order to study the influence of Mn-magnetic ordering on the Tb-magnetic sublattice. Complete characterization of TbMn1-xGaxO3 (x = 0, 0.04, 0.1)samples, including magnetization, impedance spectroscopy, and x-ray resonant scattering and neutron diffraction on powder and single crystals has been carried out. We found that keeping the same crystal structure for all compositions, Ga for Mn substitution leads to the linear decrease in T-N(Mn) and T-Mn, reflecting the reduction in the exchange interactions strength J(Mn-Mn) and the change in the Mn-O-Mn bond angles. At the same time, a strong suppression of both the induced and the separate Tb-magnetic ordering has been observed. This behavior unambiguously proves that the exchange fields J(Mn-Tb) have a strong influence on the Tb-magnetic ordering in the full temperature range below T-N(Mn) and actually stabilize the Tb-magnetic ground state.