Local structural investigation across the magnetic transition in the type-II multiferroic material ${\mathrm{FeVO}}_4$

The structural modifications associated with magnetic and multiferroic transitions in ${\mathrm{FeVO}}_4$ 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 $(\pm 0.5) K$ $\left(T_{N1}\right)$ and 15.6 $(\pm 0.5) K$ $\left(T_{N2}\right)$ in the ${\mathrm{FeVO}}_4$. The combined analysis of XRD, Raman, and XAFS spectra rules out major modification of the Fe valence state or the average $\mathrm{Fe}\text{−}{O}_n$ coordination geometry related to the transitions at $T_{N1}$ and $T_{N2}$. 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 $\mathrm{Fe}\text{−}{O}_n$ and/or $V\text{−}{O}_n$ polyhedra, likely representing the microstructural fingerprint of changes in the super-super-exchange interactions along the ${\mathrm{Fe}}^{3+}\text{−}O\text{−}{V}^{5+}\text{−}O\text{−}{\mathrm{Fe}}^{3+}$ pathway.