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.

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.

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