Unusual magnetism of layered chromium sulfides MCrS2 (M=Li, Na, K, Ag, and Au)

TL;DR

This study investigates the diverse magnetic behaviors of layered MCrS2 compounds, revealing how exchange interactions influenced by the M ion radius lead to various magnetic ground states and potential multiferroic properties.

Contribution

The paper provides a detailed ab-initio analysis explaining the magnetic ground states of MCrS2 compounds based on exchange interactions and suggests magneto-elastic coupling as a cause for multiferroicity.

Findings

Different M ions lead to various magnetic orders.

Exchange interactions depend on M ion radius.

Strong magneto-elastic coupling may cause multiferroicity.

Abstract

MCrS2 compounds (M=Li, Na, K, Cu, Ag, and Au) with triangular Cr layers show large variety of magnetic ground states ranging from 120-degree antiferromagnetic order of Cr spins in LiCrS2 to double stripes in AgCrS2, helimagnetic order in NaCrS2, and, finally, ferromagnetic Cr layers in KCrS2. On the base of ab-initio band structure calculations and an analysis of various contributions to exchange interactions between Cr spins we explain this tendency as originating from a competition between antiferromagnetic direct nearest-neighbor d-d exchange and ferromagnetic superexchange via S p states which leads to the change of the sign of the nearest neighbor interaction depending on the radius of a M ion. It is shown that other important interactions are the third-neighbor interaction in a layer and interlayer exchange. We suggest that strong magneto-elastic coupling is most probably responsible for multiferroic properties of at least one material of this family, namely, AgCrS2.