Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMoSe.

In the lacunar spinels, with the formula ABX, transition-metal ions form tightly bound B clusters resulting in exotic physical properties such as the stabilization of Néel-type skyrmion lattices, which hold great promise for energy-efficient switching devices. These properties are governed by the symmetry of these compounds with distortion of the parent noncentrosymmetric 4̅3 space group to the polar 3, with recent observation of a coexisting 2 low-temperature phase. In this study, through powder neutron diffraction, we further confirm that a metastable 2 coexists with the 3 phase in GaMoSe and we present its structure. By applying the mode crystallography approach to the distortions together with anisotropic microstrain broadening analysis, we postulate that the formation origin of the minority 2 phase stems from the high compressive stress observed in the 3 phase. Bond valence sum analysis also suggests a change in electronic configuration in the transition to 2 which could have implications on the electrical properties of the compound. We further establish the nature of the magnetic phase transition using critical exponent analysis obtained from single-crystal magnetization measurements which shows a mixture of tricritical mean-field and 3D Heisenberg behavior [β = 0.22(4), γ = 1.19(1), and δ = 6.42(1)]. Magnetoentropic mapping performed on a single crystal reveals the signature of a positive entropy region near the magnetic phase transition which corresponds to the skyrmion phase field observed in a polycrystalline sample.