Magnetic Properties of Thalium Chromium Chalcogenides

Abstract

The magnetic properties of TlCrX₂ (X = S, Se, Te), Tl₃CrS₃, TlCr₃S5, TlCr₃Se₅ and TlCr₅Se₅ have been investigated. TlCrS₂, TlCrSe₂ and Tl₃CrS₃ order ferromagnetically with Curie temperatures in the range 60–140 K. The other compounds are antiferromagnetics with negative paramagnetic Curie temperatures, whereas TlCrTe₂ has a positive paramagnetic Curie temperature. TlCrS₂ and TlCrSe₂ have a hexagonal layer structure with Cr ions sandwiched between S and Se-layers which in turn are separated by the large radius Tl-layers. The shorter Cr-Cr distance in the haxagonal planes gives rise to a stronger intralayer exchange interaction and therefore to a behaviour analogous to that of a quasi-twodimensional magnet. TlCrS₂ and TlCrSe₂ seem to represent the extremal case in the range of ACrX₂ chalcogenides with A = Cu, Ag, Na, Li, K, where with the increase of the lattice constant a in the hexagonal plane a trend towards stronger positive exchange interactions has been observed.