Effect of high pressure on competing exchange couplings in Li2VOSiO4

We report x-ray diffraction measurements on Li2VOSiO4 single crystals under pressures up to 7.6 GPa. The structure evolution under high pressure evidences a strongly anisotropic compressibility and a significant contraction of Li-O bonds. The corresponding evolution of the electronic structure was calculated ab initio. Using first-principles Wannier functions, we constructed, for several pressures, a material-specific low-energy one-band Hubbard model for the half-filled V xy bands. We found that the ratio between the next-nearest neighbor and nearest neighbor hopping integral, t2 / t1, decreases by about 23% when the pressure increases from 0 to 7.6 GPa. By means of standard superexchange theory, we estimated a corresponding decrease of about 40% in the ratio J2 /J1 between the next-nearest neighbor and nearest neighbor magnetic coupling. This suggests that one could possibly tune the ground state of this frustrated two-dimensional antiferromagnet from collinear to disordered by applying high pressures.