Local Inversion Symmetry Breaking and Thermodynamic Evidence for Ferrimagnetism in FeGaTe.

The layered compound FeGaTe is attracting attention due to its high Curie temperature, low dimensionality, and the presence of topological spin textures above room temperature, making FeGaTe a good candidate for applications in spintronics. Here, we show, through transmission electron microscopy (TEM) techniques, that FeGaTe single crystals break local inversion symmetry while maintaining global inversion symmetry according to X-ray diffraction. Coupled to the observation of Néel skyrmions via Lorentz-TEM, our structural analysis provides a convincing explanation for their presence in centrosymmetric materials. Magnetization measurements as a function of the temperature display a sharp first-order thermodynamic phase-transition leading to a reduction in the magnetic moment. This implies that the ground state of FeGaTe is globally ferrimagnetic and not a glassy magnetic state composed of ferrimagnetic, and ferromagnetic domains as previously claimed. Neutron diffraction studies indicate that the ferromagnetic-to-ferrimagnetic transition upon reducing the external magnetic field might be associated with a change in the magnetic configuration/coupling between Fe1 and Fe2 moments. We observe a clear correlation between the hysteresis observed in both the skyrmion density and the magnetization of FeGaTe. This indicates that its topological spin textures are affected by the development of ferrimagnetism upon cooling. Observation, via magnetic force microscopy, of magnetic bubbles at the magnetic phase boundary suggests skyrmions stabilized by the competition among magnetic phases and distinct exchange interactions. Our study provides an explanation for the observation of Néel skyrmions in centrosymmetric systems while exposing a correlation between the distinct magnetic phases of FeGaTe and its topological spin textures.