Layered chalcogenides of the FeGa2S₄ structure type: synthesis, crystal structure, and magnetic properties

A 2D material is a crystalline substance consisting of a single layer of atomic thickness. If any magnetically ordered material is exfoliated down to a single crystal lattice layer, its magnetic properties are likely to disappear at room temperature. This occurs due to thermal fluctuations, which readily destroy the magnetic order. The first magnetic 2D materials have recently been obtained, but most of them are unstable in air, hindering their practical application. These compounds exhibit novel magnetoelectric and magneto-optical properties, which are extremely important for spintronics. Layered chalcogenides of the FeGa2S₄ structure type represent a promising class of materials for the discovery of new two-dimensional systems.

The objective of the present work is to synthesize new layered magnetic compounds of the FeGa₂S4 structure type: FeAl₂S₄, FeAl₂Se₄, VGa₂S₄, and CrGa₂S₄, and to investigate their structure and magnetic properties. Bulk crystals of the target compounds can be used to obtain 2D materials via mechanical exfoliation, since the structural layers, bounded by sulfur or selenium atoms, are linked only by weak van der Waals interactions. This report will present the conditions for the synthesis of polycrystalline samples, as well as the growth of large bulk crystals using chemical vapor transport reactions. The crystal structure of the isostructural compounds has been studied by powder X-ray diffraction. The iron-containing compounds were also investigated by Mössbauer spectroscopy, and the selenide compound was examined by high-resolution transmission electron microscopy. The composition of the crystals was characterized by electron-probe microanalysis. The work presents measurements of the magnetic properties of the samples.