2018/08/31 by S. A. Nikolaev, I. V. Solovyev · 1 citation
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.99.100401
published as Phys. Rev. B 99, 100401 (2019)
arxiv created 2019/03/07 · arxiv updated 2019/03/13
The lacunar spinel GaV4S8 was recently suggested to be a prototype multiferroic material hosting skyrmion lattice states with a sizeable polarization \boldsymbolP coupled to magnetic order. We explain this phenomenon on the microscopic level. On the basis of density functional theory, we construct an effective model describing the behavior of magnetically active electrons in a weakly coupled lattice formed by molecular orbitals of the (V4S4)5+ clusters. By applying superexchange theory combined with the Berry-phase theory for \boldsymbolP, we derive a compass model relating the energy and polarization change with the directions of spins \boldsymbolei in magnetic bonds. We argue that, although each skyrmion layer is mainly formed by superexchange interactions in the same plane, the spin-dependence of \boldsymbolP arises from the stacking misalignment of such planes in the perpendicular direction, which is inherent to the lacunar spinel structure. We predict a strong competition of isotropic, ∼ \boldsymbolei\boldsymbolej, and antisymmetric, ∼ \boldsymbolei × \boldsymbolej, contributions to \boldsymbolP that explains the experimentally observed effect.