Local structural investigation across the magnetic transition in the type-II multiferroic material FeVO4

The structural modifications associated with magnetic and multiferroic transitions in FeVO₄ polycrystalline samples have been investigated using complementary techniques, including synchrotron radiation x-ray diffraction (XRD), Raman spectroscopy, and x-ray absorption fine-structure spectroscopy (XAFS). Temperature-dependent measurements reveal unveiled details of the local structural modifications intimately related to the spin-lattice coupling. This study is particularly focused on illuminating the changes occurring crossing the two distinct antiferromagnetic transition temperatures at 21.8 (±0.5) K (TN1) and 15.6 (±0.5) K (TN2) in the FeVO₄. The combined analysis of XRD, Raman, and XAFS spectra rules out major modification of the Fe valence state or the average Fe-Oₙ coordination geometry related to the transitions at TN1 and TN2. On the contrary, structural modifications are revealed in the Fe-Fe, Fe-V, and Fe-O-V path distances as a function of temperature, attributable to changes in the tilting and rotation of Fe-Oₙ and/or V-Oₙ polyhedra, likely representing the microstructural fingerprint of changes in the super-super-exchange interactions along the Fe³⁺-O-V⁵⁺-O-Fe³⁺ pathway.