Lattice and magnetic dynamics in the YVO3 Mott insulator studied by neutron scattering and first-principles calculations

The Mott insulator YVO3 with TN=118K is revisited to explore the role of spin, lattice, and orbital correlations across the multiple structural and magnetic transitions observed as a function of temperature. Upon cooling, the crystal structure changes from orthorhombic to monoclinic at 200 K, and back to orthorhombic at 77 K, followed by magnetic transitions. From the paramagnetic high-temperature phase, C-type magnetic ordering is first observed at 118 K, followed by a G-type spin re-orientation transition at 77 K. The dynamics of the transitions were investigated via inelastic neutron scattering and first-principles calculations. An overall good agreement between the neutron data and calculated spectra was observed. From the magnon density of states, the magnetic exchange constants were deduced to be Jab=Jc=-5.8meV in the G-type spin phase, and Jab=-3.8meV, Jc=7.6meV at 80 K and Jab=-3.0meV, Jc=6.0meV at 100 K in the C-type spin phase. Paramagnetic scattering was observed in the spin ordered phases, well below the C-type magnetic transition temperature, which continuously increased above the transition. Fluctuations in the temperature dependence of the phonon density of states were observed between 50 and 80 K as well, coinciding with the G-type to C-type transition. These fluctuations are attributed to optical oxygen modes above 40 meV, from first-principles calculations. In contrast, little change in the phonon spectra is observed across TN.