Symmetry, microscopy and spectroscopy signatures of altermagnetism

Steven

Symmetry, microscopy and spectroscopy signatures of altermagnetism

Summary

This article reviews the defining symmetry properties of altermagnetism and surveys the experimental microscopy and spectroscopy fingerprints used to identify altermagnetic order in real materials. Altermagnets are a distinct class of spin-ordered phases characterised by non-relativistic, momentum-dependent spin splitting in compensated collinear magnets. The review connects theory (spin-space group/symmetry analysis and minimal models) with experiments — ARPES/photoemission, resonant X-ray and X-ray magnetic circular dichroism, neutron and muon probes, terahertz emission and transport signatures — and highlights materials where signatures have been observed or predicted (notably MnTe, RuO2, CrSb and several 2D candidates). The piece also outlines implications for topological responses, superconductivity, magnetoelectric/ferroelectric coupling and spintronics applications.

Key Points

  • Altermagnetism is a symmetry-distinct magnetic phase producing momentum-dependent, non-relativistic spin splitting in compensated collinear magnets (d-, g- or i-wave textures).
  • Symmetry analysis via spin-space (spin) groups predicts allowed spin-splitting patterns and constrains expected spectroscopic/microscopy signals.
  • Clear experimental signatures include ARPES/angle-resolved photoemission band splittings, resonant X-ray scattering/XMCD contrasts, chiral magnon features in inelastic probes, and anomalous Hall / nonlinear transport signals despite zero net magnetisation.
  • Materials showing reported or candidate altermagnetic behaviour: MnTe (g-/d-wave spectroscopic splitting), RuO2 (anomalous Hall, terahertz emission, contested magnetic order), CrSb (direct band-splitting mapping), and several layered/2D compounds predicted by DFT and model studies.
  • Altermagnetism couples to other phenomena: it can enable unusual superconducting pairings (finite-momentum, Majorana proposals), magnetoelectric and ferroelectric switching, topological bands (Weyl/Dirac features), and device-relevant spin-current generation without net magnetisation.

Content summary

The review begins from the formal classification of altermagnets via spin-group symmetry and explains how specific point- and space-group elements enforce momentum-dependent spin splitting even when the global magnetisation is zero. It summarises theoretical developments (minimal models, Landau theory, quantum-geometry-induced nonlinear transport) and practical diagnostics: what spectroscopists and microscopists should look for and which measurement combinations give unambiguous evidence. Representative experiments are discussed — e.g. ARPES/photoemission showing band splitting in MnTe and CrSb, resonant X-ray and XMCD studies, neutron and muon probes that probe magnetic order, and transport/optical measurements (anomalous Hall, terahertz emission) providing complementary signatures. The review closes with outlooks: candidate material platforms (bulk rutile compounds, layered van der Waals, engineered heterostructures), interplay with superconductivity and ferroelectricity, and device angles for spintronics.

Context and relevance

Why this matters: altermagnetism expands the taxonomy of magnetic order and offers ways to generate strong spin-dependent electronic effects without net magnetisation or heavy spin–orbit coupling. That means potential robustness against stray-field issues and lower dissipation in spintronic devices, plus routes to topological transport and exotic superconducting states. For experimentalists, the review distils which probes are decisive; for modellers it ties symmetry constraints to observable band/magnon features; for device researchers it flags practical materials and mechanisms that could be engineered into next-generation components.

Author style

Punchy — the review is written to make the significance clear: altermagnetism isn’t a niche curiosity but a predictive symmetry-driven framework that already links to concrete experiments and device concepts. If you work in magnetism, spintronics, topological materials or superconductivity, the detailed sections and materials table are worth your time.

Why should I read this?

Short answer: if you like weird magnetism that behaves like a ferromagnet in some measurements but has zero net moment, this is the cheat-sheet. It tells you exactly what microscopes and spectrometers see, which materials actually show the effects, and why these phenomena could matter for devices — all without wading through dozens of separate papers.

Source

Source: https://www.nature.com/articles/s41586-025-09883-2

Article meta

Article Title: Symmetry, microscopy and spectroscopy signatures of altermagnetism
Article URL: https://www.nature.com/articles/s41586-025-09883-2