Variation of Triangular Antiferromagnetic Order in Ferroelectromagnetic Sc_1-xLu_xMnO₃ Manganites

Structural, magnetic, and Mn K-edge X-ray absorption near-edge structure (XANES) spectroscopic studies have been done on the stoichiometric, hexagonal Sc_1-xLu_xMnO₃ (0 ≤ x ≤ 1) system. The identical main threshold edge energy E₀ of 6545 eV indicates trivalent Mn³⁺ for all samples. The triangular antiferromagnetic (AF) Néel temperature T_N decreases monotonically, from 133 K for ScMnO₃ to 112 K for Sc_0.5Lu_0.5MnO₃ and 92 K for LuMnO₃, due to decreasing d-p hybridization in the trigonal MnO₅ block. Complex low temperature spin reorientations are observed for all samples. The K pre-edge features, with an energy separation ΔE(P₂-P₁) of 2.27 eV for ScMnO₃ and 2.31 eV for LuMnO₃, are associated with the 1s-3d quadrupole transition, which is weakly allowed through the hybridization of Mn 4p with the 3d states of neighboring Mn atoms. The P₁ peak corresponds to a transition to the e′ and e″ minority spin states in the MnO₅ crystal field, with the smaller P₂ corresponding to the leftover e′ minority spin states.