Local structural distortions and magnetism in lacunar spinel compounds*

Lacunar spinels AB₄Q₈ (A=Al, Ga, Ge; B=V, Nb, Mo, Ta; Q=S, Se) display a variety of novel phenomena including skyrmion lattices and pressure-induced insulator-metal transitions and superconductivity. The high temperature structure features unique tetrahedral transition-metal clusters with S=1/2 moments on an FCC lattice. Low temperature distortions of these clusters are crucial to the properties of lacunar spinels. In skyrmion hosts GaV₄S₈ and GaV₄Se₈, a low temperature rhombohedral distortion allows for polar and magnetic order. In GaNb₄Se₈ and GaTa₄Se₈, antiferromagnetic interactions lead to geometric frustration and a magnetic transition associated with a tetragonal distortion. We present results of local structural characterization on lacunar spinels in connection to their magnetic properties.