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arXiv · 2006.04891

Higher-order exchange interactions in two-dimensional magnets

Alexey Kartsev·Mathias Augustin·Richard F. L. Evans·Kostya S. Novoselov·Elton J. G. Santos
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Abstract

Magnetism in recently discovered van der Waals materials has opened new avenues in the study of fundamental spin interactions in truly two-dimensions. A paramount question is what effect higher-order interactions beyond bilinear Heisenberg exchange have on the magnetic properties of few-atom thick compounds. Here we demonstrate that biquadratic exchange interactions, which is the simplest and most natural form of non-Heisenberg coupling, assume a key role in the magnetic properties of layered magnets. Using a combination of nonperturbative analytical techniques, non-collinear first-principles methods and classical Monte Carlo calculations that incorporate higher-order exchange, we show that several quantities including magnetic anisotropies, spin-wave gaps and topological spin-excitations are intrinsically renormalized leading to further thermal stability of the layers. We develop a spin Hamiltonian that also contains antisymmetric exchanges (e.g. Dzyaloshinskii-Moriya interactions) to successfully rationalize numerous observations currently under debate, such as the non-Ising character of several compounds despite a strong magnetic anisotropy, peculiarities of the magnon spectrum of 2D magnets, and the discrepancy between measured and calculated Curie temperatures. Our results lay the foundation of a universal higher-order exchange theory for novel 2D magnetic design strategies.

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Alexey Kartsev, Mathias Augustin, Richard F. L. Evans, Kostya S. Novoselov, Elton J. G. Santos. 2020-06-08. Higher-order exchange interactions in two-dimensional magnets. https://doi.org/10.1038/s41524-020-00416-1

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