Magnetic structure evolution and magnetoelastic coupling across the spin reorientation transition in TmCrO3

Abstract

We present a comprehensive study of the magnetic structure evolution across the spin reorientation transition in orthorhombic (Pnma) TmCrO3. Magnetic susceptibility reveals canted antiferromagnetic (CAFM) ordering at T_N = 125 K, two compensation points (T_comp1 and T_comp2), followed by magnetization reversal with a magnetic susceptibility minimum between T_comp1 and T_comp2. Heat capacity shows a sharp lambda-type transition at T_N, associated with the long-range antiferromagnetic ordering of Cr, followed by a broad feature near 9 K. Neutron powder diffraction (NPD) establishes the Pn'm'a (Gamma2) magnetic structure below T_N. A gradual change in magnetic structure occurs during the spin-reorientation (SRO) transition below 30 K, where the magnetic symmetry transforms from Pn'm'a (Gamma2) to Pn'ma' (Gamma4) phase. However, below the SRO, neither Gamma2 nor Gamma4 alone adequately fit the intensity of magnetic reflections. A satisfactory refinement is achieved using the monoclinic subgroup P21'/c', derived from a combination of Gamma2 and Gamma4. The gradual SRO of Tm and Cr moments across the compensation regime is consistent with the magnetic symmetry P21'/c'. Furthermore, the ordered moments of Cr and Tm in TmCrO3 exhibit a complex, non-monotonic temperature dependence, with the Tm sublattice driving the spin-reorientation transition near the compensation point. Anomalies in the lattice parameters reveal strong magnetoelastic coupling, linking structural distortions to the SRO.