Spin-phonon interactions revisited: Far-infrared emission, Raman scattering, and high-resolution x-ray diffraction at the N\'eel temperature in LaFeO3

TL;DR

This study investigates the structural and magnetic interactions in LaFeO3 across its Neel temperature, revealing bond deviations, lattice distortions, and spin-phonon effects that influence its magnetic properties and phase transitions.

Contribution

It provides detailed insights into spin-phonon interactions, lattice distortions, and bond behavior at the Neel temperature in LaFeO3, enhancing understanding of magnetoelastic effects in RFeO3 perovskites.

Findings

Bond deviations reach a singular point near TN.

Sharp changes in bond lengths observed at TN.

Diffraction line intensities peak at TN indicating spin-phonon interactions.

Abstract

We report on the structural evolution, spin phonon interactions, and magnetoelastic effects in bulk LaFeO3 perovskite across its antiferromagnetic transition. We found that while the lattice constants exhibit slight deviations at the Neel temperature(TN), 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 the observed in x ray diffraction for negative thermal expansion. These bond deviations reach a singular point near TN, 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 2p hybridized states associated with the superexchange mechanism. High-resolution SXRD measurements of the c-axis Fe3+ O1 and La3+ O1 apex distances reveal a distinct inflection at the Neel temperature. This behavior supports the role of lattice distortions and crystal field modifications in the emergence of non collinear weak ferromagnetism in RFeO3 (R = rare earth) perovskites. Furthermore, our SXRD patterns show an increase in diffraction line intensities peaking at TN, 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 RFeO3 (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.