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PreprintCC BY 4.0arXiv

Hidden Magnetic Octupolar Order driven by Spin-Orbit coupling in KFeF3

  • C. A. Crawford
  • C. I. Hiley
  • N. C. Bristowe
  • C. Stock
  • J. Gainza
  • C. Ritter
  • M. R. Lees
  • R. I. Walton
  • M. S. Senn
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Abstract

Phase transitions are typically driven by symmetry-breaking structural distortions that lift electronic degeneracies, yet in some cases, these transitions may be driven by a hidden order without conventional structural signatures. Here, we demonstrate that the 3d perovskite, KFeF3, hosts such a hidden instability. Using a combination of high-resolution powder diffraction, magnetometry, symmetry-based analysis and first principles calculations, we reveal that while the 90 K cubic to rhombohedral transition arises from conventional magnetostriction accompanying antiferromagnetic order, a second transition at 40 K lowers the symmetry to monoclinic without any detectable Jahn-Teller distortion or translational symmetry-breaking. Symmetry-based Landau analysis supports a hidden zone centered magnetic octupole order parameter, whose improper coupling accounts for the weak ferromagnetism and pronounced symmetry-breaking strain. Density functional calculations show that spin-orbit coupling suppresses the competing Jahn-Teller instability, and thereby favors higher rank magnetic multipolar degrees of freedom. These findings establish KFeF3 as a model system in which the competing energy scales between spin-orbit coupling and orbital degeneracy result in the emergence of hidden, multipolar order. We show that the control of such magnetic, multipolar order could, in principle, provide a route to induce altermagnetism.

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Cite

BibTeXRIS
BibTeX
@misc{crawford2026hidden,
  title = {{Hidden Magnetic Octupolar Order driven by Spin-Orbit coupling in KFeF$_3$}},
  author = {C. A. Crawford and C. I. Hiley and N. C. Bristowe and C. Stock and J. Gainza and C. Ritter and M. R. Lees and R. I. Walton and M. S. Senn},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.03684},
  eprint = {2609.03684},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.03684},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Hidden Magnetic Octupolar Order driven by Spin-Orbit coupling in KFeF_3
AU  - C. A. Crawford
AU  - C. I. Hiley
AU  - N. C. Bristowe
AU  - C. Stock
AU  - J. Gainza
AU  - C. Ritter
AU  - M. R. Lees
AU  - R. I. Walton
AU  - M. S. Senn
PY  - 2026
DA  - 2026/09/03
PB  - arXiv
DO  - 10.48550/arxiv.2609.03684
UR  - https://arxiv.org/abs/2609.03684
AB  - Phase transitions are typically driven by symmetry-breaking structural distortions that lift electronic degeneracies, yet in some cases, these transitions may be driven by a hidden order without conventional structural signatures. Here, we demonstrate that the 3d perovskite, KFeF_3, hosts such a hidden instability. Using a combination of high-resolution powder diffraction, magnetometry, symmetry-based analysis and first principles calculations, we reveal that while the 90 K cubic to rhombohedral transition arises from conventional magnetostriction accompanying antiferromagnetic order, a second transition at 40 K lowers the symmetry to monoclinic without any detectable Jahn-Teller distortion or translational symmetry-breaking. Symmetry-based Landau analysis supports a hidden zone centered magnetic octupole order parameter, whose improper coupling accounts for the weak ferromagnetism and pronounced symmetry-breaking strain. Density functional calculations show that spin-orbit coupling suppresses the competing Jahn-Teller instability, and thereby favors higher rank magnetic multipolar degrees of freedom. These findings establish KFeF_3 as a model system in which the competing energy scales between spin-orbit coupling and orbital degeneracy result in the emergence of hidden, multipolar order. We show that the control of such magnetic, multipolar order could, in principle, provide a route to induce altermagnetism.
ER  -