Landau theory and exchange instabilities in Mn5Si3: A case against strain-induced altermagnetism
Abstract
Thin-film Mn5Si3 is a prominent altermagnetic candidate owing to its metallicity, demonstrated anisotropic anomalous transport, and proposed d-wave exchange splitting that could enable spin-polarized transport. Its postulated altermagnetic structure has zero propagation vector, unlike the bulk collinear antiferromagnetic AFM2 phase, which orders at the M star. We analyze both phases using Landau theory, first-principles paramagnetic-instability calculations, and Monte Carlo simulations. AFM2 appears in Landau theory as a symmetry-protected inversion-even, permutation-odd mode at a single arm of the M star. At Γ, the same intracell pattern belongs to the collinear sector of an E2g order parameter; both phases require higher-order terms for their selection. Disordered-local-moment calculations identify the leading exchange instability at M, and the resulting classical Heisenberg model orders at the bulk experimental temperature scale into the orthogonal 3M phase favored by single-site entropy. Magnetostructural coupling to E2g deformations favors single-M AFM2 ordering. The estimated homogeneous-strain contribution to the relevant quartic coefficient is about a quarter of the competing entropic term near the bulk transition, while internal E2g relaxations are expected to provide additional stabilization. The Γ-point E2g mode, whose Landau theory contains the altermagnetic sector, is substantially weaker and further suppressed by epitaxial strain comparable to that reported for Mn5Si3/Si(111) films exhibiting anomalous transport. The same strain reduces the leading magnetic exchange scale. These results explain the bulk M-point instability but strongly disfavor relocating the propagation vector from M to Γ in a moderately strained bulklike Mn5Si3 film, leaving the identity of the Hall-active phase unresolved.
Related
- Landau Theory for Non-relativistic Magnetism Beyond Altermagnetism
- Landau-like formalism for the thermal-runaway and filamentation instabilities in switching Mott devices
- Altermagnetism and generalised tensorial properties in the exchange multiplet framework
- Moiré-induced altermagnetism from nonmagnetic constituents
- Altermagnetism-induced higher-order topological Dirac semimetals in two-dimensional nonsymmorphic systems
BibTeX
@misc{belashchenko2026landau,
title = {{Landau theory and exchange instabilities in Mn$_5$Si$_3$: A case against strain-induced altermagnetism}},
author = {K. D. Belashchenko},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.13483},
eprint = {2608.13483},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.13483},
}
RIS
TY - UNPB
TI - Landau theory and exchange instabilities in Mn_5Si_3: A case against strain-induced altermagnetism
AU - K. D. Belashchenko
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2608.13483
UR - https://arxiv.org/abs/2608.13483
AB - Thin-film Mn_5Si_3 is a prominent altermagnetic candidate owing to its metallicity, demonstrated anisotropic anomalous transport, and proposed d-wave exchange splitting that could enable spin-polarized transport. Its postulated altermagnetic structure has zero propagation vector, unlike the bulk collinear antiferromagnetic AFM2 phase, which orders at the M star. We analyze both phases using Landau theory, first-principles paramagnetic-instability calculations, and Monte Carlo simulations. AFM2 appears in Landau theory as a symmetry-protected inversion-even, permutation-odd mode at a single arm of the M star. At Γ, the same intracell pattern belongs to the collinear sector of an E_2g order parameter; both phases require higher-order terms for their selection. Disordered-local-moment calculations identify the leading exchange instability at M, and the resulting classical Heisenberg model orders at the bulk experimental temperature scale into the orthogonal 3M phase favored by single-site entropy. Magnetostructural coupling to E_2g deformations favors single-M AFM2 ordering. The estimated homogeneous-strain contribution to the relevant quartic coefficient is about a quarter of the competing entropic term near the bulk transition, while internal E_2g relaxations are expected to provide additional stabilization. The Γ-point E_2g mode, whose Landau theory contains the altermagnetic sector, is substantially weaker and further suppressed by epitaxial strain comparable to that reported for Mn_5Si_3/Si(111) films exhibiting anomalous transport. The same strain reduces the leading magnetic exchange scale. These results explain the bulk M-point instability but strongly disfavor relocating the propagation vector from M to Γ in a moderately strained bulklike Mn_5Si_3 film, leaving the identity of the Hall-active phase unresolved.
ER -