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Title: Biquadratic exchange interactions in two-dimensional magnets
Authors: Kartsev, A.
Augustin, M.
Evans, R.F.L.
Novoselov, K.S. 
Santos, E.J.G.
Issue Date: Dec-2020
Publisher: Nature Research
Citation: Kartsev, A., Augustin, M., Evans, R.F.L., Novoselov, K.S., Santos, E.J.G. (2020-12). Biquadratic exchange interactions in two-dimensional magnets. npj Computational Materials 6 (1) : 150. ScholarBank@NUS Repository.
Rights: Attribution 4.0 International
Abstract: Magnetism in recently discovered van der Waals materials has opened several 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, 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 provide a theoretical framework for the exploration of different physical phenomena in 2D magnets where biquadratic exchange interactions have an important contribution. © 2020, The Author(s).
Source Title: npj Computational Materials
ISSN: 20573960
DOI: 10.1038/s41524-020-00416-1
Rights: Attribution 4.0 International
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