Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo4Se8

In the AB(4)Q(8) lacunar spinels, the electronic structure is described on the basis of inter- and intracluster interactions of tetrahedral B-4 clusters, and tuning these can lead to myriad fascinating electronic and magnetic ground states. In this work, we employ magnetic measurements, synchrotron x-ray and neutron scattering, and first-principles electronic structure calculations to examine the coupling between structural and magnetic phase evolution in GaMo4Se8, including the emergence of a skyrmionic regime in the magnetic phase diagram. We show that the competition between two distinct Jahn-Teller distortions of the room temperature cubic F (4) over bar 3m structure leads to the coexistence of the ground-state R3m phase and a metastable Imm2 phase. The magnetic properties of these two phases are computationally shown to be very different, with the Imm2 phase exhibiting uniaxial ferromagnetism and the R3m phase hosting a complex magnetic phase diagram including equilibrium Neel-type skyrmions stable from nearly T = 28 K down to T = 2 K, the lowest measured temperature. The large change in magnetic behavior induced by a small structural distortion reveals that GaMo4Se8 is an exciting candidate material for tuning unconventional magnetic properties via mechanical means.