Structural distortions and magnetism in transition-metal cluster compound GaNb₄Se₈

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 GaNb₄Se₈, antiferromagnetic interactions lead to geometric frustration and a magnetic transition associated with a tetragonal distortion, proposed to be a singlet state at low temperatures. We present results of structural characterization on lacunar spinel GaNb₄Se₈ under temperature and pressure in connection to its magnetic properties.