Single-ion anisotropy, Dzyaloshinskii-Moriya interaction, and negative magnetoresistance the spin-1/2 pyrochlore R2V2O7

The electronic and magnetic properties of spin-1/2 pyrochlores R2V2O7 were investigated on the basis of density-functional calculations. Contrary to common belief, the spin-1/2 V4+ ions are found to have a substantial easy-axis single-ion anisotropy. We show that the magnon quantum Hall effect of Lu2V2O7 is a combined consequence of the easy-axis single-ion anisotropy and the Dzyaloshinskii-Moriya interaction of the spin-1/2 V4+ ions. We also show that the negative magnetoresistance observed for R2V2O7 arises from a different mechanism, i.e., the band gap decreases as the spin alignment becomes more parallel to each other.