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

TL;DR

This study uses density-functional calculations to reveal significant single-ion anisotropy in spin-1/2 pyrochlores R2V2O7, explaining negative magnetoresistance through a new mechanism and clarifying discrepancies in D/J ratio estimates.

Contribution

It demonstrates the importance of single-ion anisotropy in R2V2O7 and resolves previous inconsistencies in D/J ratio estimations.

Findings

V4+ ions exhibit substantial easy-axis single-ion anisotropy.

Discrepancy in D/J ratio explained by neglecting single-ion anisotropy.

Negative magnetoresistance arises from a new mechanism.

Abstract

The electronic and magnetic properties of spin-1/2 pyrochlores R2V2O7 were investigated on the basis of density-functional calculations. Contrary to the common belief, the spin-1/2 V4+ ions are found to have a substantial easy-axis single-ion anisotropy. The |D/J| ratio deduced from the magnon quantum Hall effect of Lu2V2O7, where J is the nearest-neighbor spin exchange and D is the Dzyaloshinskii-Moriya parameter, is much greater than the value estimated from our calculations (i.e., 0.32 vs. 0.05). We show that this discrepancy is due to the neglect of the single-ion anisotropy of the V4+ ions, and the negative magnetoresistance observed for R2V2O7 arises from a new mechanism.