A Mössbauer investigation of orthorhombic phase YbMnO3

¹⁷⁰Yb- and ⁵⁷Fe-Mössbauer spectra are reported for orthorhombic phase manganites YbMnO₃ and Yb(⁵⁷Fe_0.005Mn_0.995)O₃, respectively. Point charge model estimates of the electric field gradient agree well with experimental ⁵⁷Fe-Mössbauer results in terms of both sign and magnitude of the electric quadrupole interaction strength, and the orientation of the magnetic hyperfine field is consistent with an E-type antiferromagnetic order where Mn moments are aligned along the a-axis (Pnma notation). The ¹⁷⁰Yb-Mössbauer spectra exhibit pure quadrupole splitting down to 1.8 K, contradicting an earlier report that the Yb sub-lattice orders in it own right at T_Yb ≈ 4 K. Nevertheless, there is a slight increase in line broadening with decreasing temperature, probably due to the weak magnetic exchange field arising out of the ordered Mn sub-lattice. The small variation with temperature of the quadrupole interaction strength suggests that the Yb³⁺ electronic ground state is a well-isolated Kramers doublet.