We report on the structural evolution, spin-phonon interactions, and magnetoelastic effects in bulk ${\mathrm{LaFeO}}_3$ perovskite across its antiferromagnetic transition. Our investigation is motivated by anomalies in the zone-center phonon bandwidth and peak positions which, as superexchange precursors, deviate in far-infrared emission and high-temperature Raman scattering spectra from the behavior expected in a purely anharmonic lattice. High-resolution synchrotron x-ray diffraction (SXRD) patterns provide intriguing insights into the interplay between the perovskite lattice and the magnetic transition. We found that, while the lattice constants exhibit slight deviations at the Néel temperature ($T_{\mathrm{N}}$), due to spin-phonon interactions, individual interatomic bonds display distinct behavior. The octahedral B-site basal plane, involving oxygen ion pairs that mediate superexchange interactions, displays bond contraction (or elongation) assimilable to that observed in x-ray diffraction for negative thermal expansion. These bond deviations reach a singular point near $T_{\mathrm{N}}$, where a sharp change in bond length is observed. A similar abrupt change is also detected in the nearest-neighbor La–O2 basal plane distances, which we interpret as arising from ion size differences within the $3d\text{−}2p$ hybridized states associated with the superexchange mechanism. High-resolution SXRD measurements of the c axis $\mathrm{F}{\mathrm{e}}^{3+}\text{–}\mathrm{O}1$ and $\mathrm{L}{\mathrm{a}}^{3+}\text{–}\mathrm{O}1$ apex distances reveal a distinct inflection at the Néel temperature. This behavior supports the role of lattice distortions and crystal field modifications in the emergence of noncollinear weak ferromagnetism in $R\text{Fe}{\mathrm{O}}_3$ ($R=$ rare earth) perovskites. Furthermore, our SXRD patterns show an increase in diffraction line intensities peaking at $T_{\mathrm{N}}$, suggesting a straightforward indicator for spin-phonon interactions that also resolves into lattice metastability deduced by nonlinear thermal expansion in the paramagnetic phase. Preliminary results across the full $R\text{Fe}{\mathrm{O}}_3$ ($R=$ rare earth) series indicate a shared structural framework among all members, potentially offering insights into previously inconclusive structural interpretations in oxides with common octahedral sublattices.

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• Magnetic coupling
• Magnetic interactions
• Magnetism
• Phase transitions
• Phonons
• Antiferromagnets
• Magnetic insulators
• Multiferroics
• Fourier transform infrared spectroscopy
• Infrared spectroscopy
• Interferometry
• Light scattering
• Raman spectroscopy
• Terahertz spectroscopy
• X-ray diffraction