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Published November 7, 2025 | Version Published
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Magnons in chromium trihalides calculated with the ab initio Bethe-Salpeter equation

Creators

  • 1. ROR icon University of Valencia
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon Institute of Structure of Matter

Abstract

Chromium trihalides (Cr⁢𝑋3, with 𝑋⁢=I,Br,Cl) are layered ferromagnetic materials with rich physics and possible applications. Their structure consists of magnetic Cr atoms sandwiched between two layers of halide atoms. Different halide atoms result in distinct magnetic properties, but their effect on spin-wave (magnon) excitations is not fully understood. Here we show first-principles calculations of magnon dispersions and wave functions in monolayer Cr trihalides using the finite-momentum Bethe-Salpeter equation (BSE) to describe collective spin-flip excitations. We study the dependence of magnon dispersions on the halide species and resolve the small topological gap at the Dirac point in the magnon spectrum by including spin-orbit coupling. Analysis of magnon wave functions reveals that magnons are made up of electronic transitions with a wider energy range than excitons in Cr⁢𝑋3 monolayers, providing insight into magnon states in real and reciprocal space. We analyze Heisenberg exchange parameters extracted from the BSE and discuss the convergence of BSE magnon calculations. Our work advances the quantitative modeling of magnons, providing the starting point for studying magnon interactions in a first-principles BSE framework.

Copyright and License

©2025 American Physical Society.

Acknowledgement

This work is supported by the European Union's Horizon Europe research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 101118915 (TIMES). This work is part of the project I +D +i PID2020-112507GB-I00 QUANTA-2DMAT, funded by MCIN/AEI/10.13039/501100011033, Project No. PROMETEO/2021/082 (ENIGMA) and SEJIGENT/2021/034 (2D-MAGNONICS) funded by the Generalitat Valenciana. This study is also part of the Advanced Materials program (Project No. SPINO2D), supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Generalitat Valenciana. A.M.-S. acknowledges the Ramón y Cajal program (Grant No. RYC2018-024024-I; MINECO, Spain). A.E.-K. acknowledges the Contrato Predoctoral Ref. PRE2021-097581. D.S. acknowledges funding from MaX “MAterials design at the eXascale” (Grant Agreement No. 101093374) cofunded by the European High Performance Computing Joint Undertaking (JU) and participating countries, and from the Innovation Study Isolv-BSE that has received funding through the Inno4scale project, which is funded by the European High-Performance Computing Joint Undertaking (JU) (Grant Agreement No. No 101118139). K.B.L. and M.B. were supported by the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research and Office of Basic Energy Sciences, Scientific Discovery through Advanced Computing (SciDAC) program under Award No. DE-SC0022088 for method development, by the National Science Foundation (NSF) under Grant No. OAC-2209262 for code development, and by Air Force Office of Scientific Research (AFOSR) and Clarkson Aerospace under Grants No. FA9550-21-1-0460 and No. FA9550-24-1-0004 for calculations on 2D materials. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231.

Data Availability

The data that support the findings of this article are openly available 

  • E.-K. Ali, L. Khoa, G.-C. Alberto, B. Marco, S. Davide, and M.-S. Alejandro, “Magnons in chromium trihalides calculated with the ab initio Bethe-Salpeter equation”, Materials Cloud Archive (2025), https://doi.org/10.24435/materialscloud:m0-pa.

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Additional details

Related works

References
Journal Article: 10.1103/489b-n5pd (DOI)

Funding

Ministerio de Ciencia, Innovación y Universidades
Generalitat Valenciana
RYC2018-024024-I
National Science Foundation
United States Department of Energy
DE-SC0022088
United States Department of Energy
DE-AC02-05CH11231
United States Air Force Office of Scientific Research
FA9550-21-1-0460
United States Air Force Office of Scientific Research
FA9550-24-1-0004

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Caltech groups
Division of Engineering and Applied Science (EAS) , Physics Department
Publication Status
Published