Spin-lattice coupling and frustrated magnetism in Fe-doped hexagonal LuMnO₃

Strong spin-lattice coupling and prominent frustration effects observed in the 50% Fe-doped frustrated hexagonal (h)LuMnO₃ are reported. A Néel transition at T_N ≈ 112K and a possible spin re-orientation transition at T_SR ≈ 55K are observed in the magnetization data. From neutron powder diffraction data, the nuclear structure at and below 300K was refined in polar P6₃cm space group. While the magnetic structure of LuMnO₃ belongs to the γ₄ (P6₃' 3c' m) representation, that of LuFe_0.5Mn_0.5O₃ belongs to γ₁ (P6₃cm) which is supported by the strong intensity for the (100) reflection and also judging by the presence of spin-lattice coupling. The refined atomic positions for Lu and Mn/Fe indicate significant atomic displacements at T_N and T_SR which confirms strong spin-lattice coupling. Our results complement the discovery of room temperature multiferroicity in thin films of hLuFeO₃ and would give impetus to study LuFe_1-xMn_xO₃ systems as potential multiferroics where electric polarization is linked to giant atomic displacements.