Magnetic structure evolution and magnetoelastic coupling across the spin reorientation transition in TmCrO 3

We present a comprehensive study of the magnetic structure evolution, employing bulk magnetization and neutron powder diffraction (NPD) measurements down to 3.5 K, across the spin reorientation transition in orthorhombic (Pnma) TmCrO₃. Magnetic susceptibility reveals canted antiferromagnetic (CAFM) ordering at TN=1250.16em0exK, followed by the magnetization reversal, showing minima between the two compensation points Tcomp1 and Tcomp2. Heat capacity shows a {λ}-transition at TN, associated with long-range antiferromagnetic order of Cr, followed by a broad feature at {~} 9 K, arising due to Schottky-type anomaly. Magnetic refinement of NPD data establishes the Pn^'m^'a: {Γ}2(Cₓ,Gy;CₓTm,4pt0exFzTm) CAFM structure below TN. A gradual change in magnetic structure occurs during the spin-reorientation (SRO) transition below 30 K. During this, the magnetic structure gradually changes from Pn^'m^'a ({Γ}2) to Pn^'ma^' ({Γ}4): Aₓ,Fy,4pt0exGz;FyTm. Below 30 K, however, neither {Γ}2 nor {Γ}4 alone adequately fit the intensity of magnetic reflections. A satisfactory refinement could only be achieved in the monoclinic subgroup P2^'₁/c^' derived from a combination of {Γ}2 and {Γ}4. The observed gradual SRO of Tm and Cr moments is consistent with the magnetic symmetry P2^'₁/c^': Cₓ,Gy,4pt0exGz;CₓTm,4pt0exFyTm,FzTm. Furthermore, the ordered moments Cr and Tm in TmCrO₃ exhibit a complex, nonmonotonic temperature dependence as expected during SRO. Anomalies in lattice parameters suggest magnetoelastic coupling, linking structural distortions to the SRO.