New Submissio Evidence of spin-phonon interactions in single-phase O-LuFeO₃ around T_N~623 K

Peak position and bandwidth deviations after nonmagnetic baseline corrections of far infrared and Raman zone center phonons motivated us to examine high-resolution X-ray diffraction patterns of single-phase orthorhombic LuFeO₃ Pbnm (D^2h ₁₆) across its Néel temperature in the ID22 beamline at the European Synchrotron Research Facility, Grenoble. We found that in the 300 K-1100 K range, Rietveld refinement yields only minute magnetic-induced lattice changes that deviate from linearity, which may be strongly enhanced by interval and temperature ramping changes in the measuring protocol. It induces about T_N differences 49.0 10^-4 Å ; 5.69 10^-4 Å; 143.0 10^-4 Å (673 K) in the orthorhombic a , b, c lattice constants, conclusively revealing the spin-phonon interactions as well as the latent delicate balance of short- and long-range interactions in LuFeO₃ anharmonic environment that has as a backdrop the metastable hexagonal polymorphism. Sublattice changes in basal Fe^3+-O2 bonds share with Fe³⁺-O1 apical distance (and in the Lu³⁺-O1 lengths) clear anomalies that strongly suggest that spin order coupled to lattice displacements stabilizes non-collinearity when the distortion of polarizable oxygen octahedra changes the local crystal field away from the crystallographic axes. It prevails over inducing canting Dzyaloshinskii–Moriya antisymmetric exchanges. These alterations are also found in nearest neighbor octahedra Lu³⁺-O2 basal bond length distances, which, being Lu³⁺ magnetic inert, point to a main oxygen ion role in exchange and anisotropies. Lines in the LuFeO₃ X-Ray patterns increase in intensity as the antiferromagnetic correlations dilute with increasing temperatures.