Thickness-dependent magnetic order and phase transition in V5S8**Project supported by the National Natural Science Foundation of China (Grant Nos. 51922011 and 61888102), the National Key Research & Development Project of China (Grant Nos. 2016YFA0202300 and 2019YFA0308500), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000 and XDB28000000). A portion of the research was performed in

Abstract

V5S8 is an ideal candidate to explore the magnetism at the two-dimensional (2D) limit. A recent experiment has shown that the V5S8 thin films exhibit an antiferromagnetic (AFM) to ferromagnetic (FM) phase transition with reducing thickness. Here, for the first time, using density functional theory calculations, we report the antiferromagnetic order of bulk V5S8, which is consistent with the previous experiments. The specific antiferromagnetic order is reproduced when Ueff = 2 eV is applied on the intercalated vanadium atoms within LDA. We find that the origin of the magnetic ordering is from superexchange interaction. We also investigate the thickness-dependent magnetic order in V5S8 thin films. It is found that there is an antiferromagnetic to ferromagnetic phase transition when V5S8 is thinned down to 2.2 nm. The main magnetic moments of the antiferromagnetic and ferromagnetic states of the thin films are located on the interlayered vanadium atoms, which is the same as that in the bulk. Meanwhile, the strain in the thin films also influences the AFM–FM phase transition. Our results not only reveal the magnetic order and origin in bulk V5S8 and thin films, but also provide a set of parameters which can be used in future calculations.