Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo<sub>4</sub>Se<sub>8</sub>

Routledge, Kieran, Vir, Praveen, Cook, Nicholas, Murgatroyd, Philip AE, Ahmed, Sheikh J, Savvin, Stanislav N, Claridge, John B ORCID: 0000-0003-4849-6714 and Alaria, Jonathan ORCID: 0000-0001-5868-0318
(2021) Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo<sub>4</sub>Se<sub>8</sub>. CHEMISTRY OF MATERIALS, 33 (14). pp. 5718-5729.

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In the lacunar spinels, with the formula AB<sub>4</sub>X<sub>8</sub>, transition-metal ions form tightly bound B<sub>4</sub> 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 <i>F</i>4̅3<i>m</i> space group to the polar <i>R</i>3<i>m</i>, with recent observation of a coexisting <i>Imm</i>2 low-temperature phase. In this study, through powder neutron diffraction, we further confirm that a metastable <i>Imm</i>2 coexists with the <i>R</i>3<i>m</i> phase in GaMo<sub>4</sub>Se<sub>8</sub> 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 <i>Imm</i>2 phase stems from the high compressive stress observed in the <i>R</i>3<i>m</i> phase. Bond valence sum analysis also suggests a change in electronic configuration in the transition to <i>Imm</i>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.

Item Type: Article
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 11 Aug 2021 13:48
Last Modified: 17 Oct 2023 21:28
DOI: 10.1021/acs.chemmater.1c01448
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