# Expanded Heisenberg Hamiltonians from a Mn/Bi DFT+U study on hexagonal antiferromagnet CaMn2Bi2: excitations and strain-controlled magnetic anisotropy switching

## TL;DR

This paper studies the magnetic properties of CaMn2Bi2 using advanced computational methods, revealing how strain can control magnetic anisotropy for potential spintronic applications.

## Contribution

The study introduces an extended Heisenberg model with local magnetization terms and demonstrates strain-controlled magnetic anisotropy switching in CaMn2Bi2.

## Key findings

- A standard Heisenberg model fails to describe magnetic excitations in CaMn2Bi2.
- An extended model with local on-site magnetization terms accurately captures magnetic behavior.
- Strain can switch the preferred magnetization direction in the plane due to spin-orbit coupling and lattice distortions.

## Abstract

The manganese pnictide CaMn\documentclass[12pt]{minimal}
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\begin{document}$$_2$$\end{document} exhibits narrow-gap antiferromagnetism with Mn atoms arranged in a puckered honeycomb structure, and is currently a promising candidate for ultra-fast light control of AFM states. In this paper, we perform a detailed study of the magnetic properties of CaMn\documentclass[12pt]{minimal}
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\begin{document}$$_2$$\end{document} using density functional theory (DFT) combined with the Hubbard U correction and spin-orbit coupling, which accurately describe the magnetic configurations. In DFT+U approach, we apply an on-site U not only to Mn-3d orbitals but also to Bi-6p ones to improve the description of Mn–Bi hybridization and the small SOC-driven gap. We show that a standard Heisenberg spin model is insufficient to describe these magnetic excitations, and an extended model accurately describes these using local on-site magnetization terms, linked to the Néel vector and inspired by Hubbard-model physics. We further investigate the role of the spin-orbit coupling, and find that the magnetic anisotropy of CaMn\documentclass[12pt]{minimal}
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\begin{document}$$_2$$\end{document}Bi\documentclass[12pt]{minimal}
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\begin{document}$$_2$$\end{document} shows an easy plane, with the preferred magnetization direction being exchanged between axes in the plane by applying small strain values. This strain-tunable magnetization, driven by the interplay between spin-orbit interactions and lattice distortions, highlights the potential for controlling magnetic states in Mn-pnictides for future applications in spintronic and magneto-optical devices.