Incommensurate magnetic ordering in CrB$_2$

TL;DR

This paper investigates incommensurate magnetic ordering in CrB$_2$ using a spin model derived from density functional theory, revealing the importance of the disordered local moment approach and explaining the material's magnetic properties.

Contribution

It introduces a detailed spin model based on density functional theory that accurately predicts the incommensurate magnetic order in CrB$_2$ and highlights the significance of the disordered local moment method.

Findings

The disordered local moment theory provides a more realistic description of CrB$_2$'s magnetism.

The calculated incommensurate spin spiral vector closely matches experimental data.

The model explains the low Néel temperature due to geometric frustration.

Abstract

Incommensurate magnetism in CrB$_2$ is studied in terms of a spin model based on density functional theory calculations. Heisenberg exchange interactions derived from the paramagnetic phase using the disordered local moment theory show significant differences compared with those resulting from the treatment of the material as a ferromagnet; of these two methods, the disordered local moment theory is found to give a significantly more realistic description. We calculate strongly ferromagnetic interactions between Cr planes but largely frustrated interactions within Cr planes. Although we find that the ground state ordering vector is sensitive to exchange interactions over a large number of neighbour shells, the $q$-vector of the incommensurate spin spiral state is satisfactorily reproduced by the theory ($0.213$ compared with the known ordering vector $0.285\times (2\pi)/(a/2)$ along $\Gamma-{\rm K}$). The strong geometric frustration of the exchange interactions causes a rather low N\'eel temperature (about 97 K), also in good agreement with experiment.