Entropy-Driven Altermagnetism from Thermal Magnons

Abstract

We identify a route to altermagnetism driven by entropy upon heating and demonstrate it in a minimal square-lattice antiferromagnet. An exchange modulation is entropically favored because the resulting momentum-dependent magnon splitting increases the magnon entropy, thereby lowering the free energy and favoring altermagnetism. We derive an instability criterion for this exchange-modulated state, predict its temperature-driven reentrant behavior, and show that its overlap with Néel order defines a finite-temperature altermagnetic phase. Variational spin-wave theory, spin--lattice Monte Carlo, and cluster diagonalization establish the entropy-driven instability and its coexistence with magnetic order. The resulting state supports a transverse spin conductivity. The mechanism provides a route to thermally induced altermagnetism in compensated magnets coupled to sufficiently soft physical modes.

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BibTeX RIS

BibTeX

@misc{halder2026entropydriven,
  title = {{Entropy-Driven Altermagnetism from Thermal Magnons}},
  author = {Tanaya Halder and Ashis K. Nandy and Anamitra Mukherjee},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.40002},
  eprint = {2609.40002},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.40002},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Entropy-Driven Altermagnetism from Thermal Magnons
AU  - Tanaya Halder
AU  - Ashis K. Nandy
AU  - Anamitra Mukherjee
PY  - 2026
DA  - 2026/09/30
PB  - arXiv
DO  - 10.48550/arxiv.2609.40002
UR  - https://arxiv.org/abs/2609.40002
AB  - We identify a route to altermagnetism driven by entropy upon heating and demonstrate it in a minimal square-lattice antiferromagnet. An exchange modulation is entropically favored because the resulting momentum-dependent magnon splitting increases the magnon entropy, thereby lowering the free energy and favoring altermagnetism. We derive an instability criterion for this exchange-modulated state, predict its temperature-driven reentrant behavior, and show that its overlap with Néel order defines a finite-temperature altermagnetic phase. Variational spin-wave theory, spin--lattice Monte Carlo, and cluster diagonalization establish the entropy-driven instability and its coexistence with magnetic order. The resulting state supports a transverse spin conductivity. The mechanism provides a route to thermally induced altermagnetism in compensated magnets coupled to sufficiently soft physical modes.
ER  -

Abstract

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