Order from disorder phenomena in BaCoS2

Abstract

At TN ≃ 300K the layered insulator BaCoS2 transitions to a columnar antiferromagnet that signals non-negligible magnetic frustration despite the relatively high TN, all the more surprising given its quasi two-dimensional structure. Here, we show, by combining ab initio and model calculations, that the magnetic transition is an order-from-disorder phenomenon, which not only drives the columnar magnetic order, but also the inter-layer coherence responsible for the finite Néel transition temperature. This uncommon ordering mechanism, actively contributed by orbital degrees of freedom, hints at an abundance of low energy excitations above and across the Néel transition, in agreement with experimental evidence.

Anatomy of Hidden Dzyaloshinskii–Moriya Interactions and Topological Spin Textures in Centrosymmetric Crystals

“…The magnetic anisotropy K xz = E [001] – E [100] = 0.37 meV/atom and K yz = E [001] – E [010] = −0.23 meV/atom favor the uniaxial magnetization along [100]. The density functional theory-resolved magnetic state of BaCoS 2 is thus in good agreement with experiments. − …”

“…Next, we apply the synthesized BaCoS 2 as an example to elucidate the LISB-induced hidden DMI in realistic systems (see the Supporting Information for details of the first-principles calculations). BaCoS 2 is a layered quasi-two-dimensional material − belonging to orthorhombic point group D 2 h , with non-equivalent a = 6.44 Å and b = 6.49 Å. For the monolayer, the CoS 5 pyramidal polyhedron is oriented alternatively about the basal plane, and its basal edge is shared with the neighbor, sandwiched by Ba atoms (Figure a).…”