{
  "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 3$d$ 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.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.03684",
  "author_total": 9,
  "authors": [
    {
      "name": "C. A. Crawford"
    },
    {
      "name": "C. I. Hiley"
    },
    {
      "name": "N. C. Bristowe"
    },
    {
      "name": "C. Stock"
    },
    {
      "name": "J. Gainza"
    },
    {
      "name": "C. Ritter"
    },
    {
      "name": "M. R. Lees"
    },
    {
      "name": "R. I. Walton"
    },
    {
      "name": "M. S. Senn"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/79m5eexmv3vsx.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.03684",
  "fulltext_url": null,
  "id": "79m5eexmv3vsx",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.03684",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "cond-mat.str-el"
    ],
    [
      "openalex",
      "2504|Magnetic and transport properties of perovskites and related materials"
    ]
  ],
  "openalex": "W7208732852",
  "pdf_url": "https://arxiv.org/pdf/2609.03684",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/79m5eexmv3vsx.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:31Z",
      "native_id": "2609.03684",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.03684"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.str-el",
      "subfield": "condensed-matter"
    }
  ],
  "title": "Hidden Magnetic Octupolar Order driven by Spin-Orbit coupling in KFeF$_3$",
  "title_text": "Hidden Magnetic Octupolar Order driven by Spin-Orbit coupling in KFeF_3",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:31Z",
  "url": "https://research.draconitic.com/paper/79m5eexmv3vsx",
  "venue": "arXiv",
  "versions": []
}