Controversy over the local magnetization magnitude in RuO2

Ascertain the true magnitude of the local magnetic moment in rutile RuO2 and resolve the controversy regarding the reported value of approximately 0.05 μB per Ru atom by reconciling experimental measurements with theoretical predictions for collinear antiparallel ordering and large altermagnetic spin splitting.

Background

RuO2 is a prototypical metallic altermagnet with predicted large spin splitting (~1.3 eV) and experimentally observed collinear antiparallel ordering at room temperature. Despite these findings, reported local magnetization values around 0.05 μB remain debated.

Resolving the magnitude and origin of the local moment is crucial for interpreting transport, optical, and dynamical phenomena in RuO2 and for benchmarking theories of altermagnetism against experiment.

References

Despite traditionally being considered a Pauli paramagnet, recently a room-temperature collinear antiparallel magnetic ordering was discovered in both RuO$_2$ bulk crystals and thin films, however, the reported small local magnetization value of $0.05\,\mathrm{\mu_B}$ still remains an open controversial issue.

— Spin and Orbital Magnetism by Light in Rutile Altermagnets  (2403.10235 - Adamantopoulos et al., 2024) in Introduction

Although the intrinsic magnetic ground state of bulk RuO2 remains controversial, several thin-film experiments have reported transport and spectroscopic signatures consistent with altermagnetic order.

— Spin-Polarized Magnetic Metal Electrodes for Magnetic Tunnel Junctions  (2609.29857 - Duan et al., 24 Sep 2026) in Section 6, paragraph beginning “For the present focus on magnetic metallic electrodes”

However, despite strong theoretical support, experimental investigations of \ce{RuO2} have yielded contradictory results. While some macroscopic transport measurements (such as the anomalous Hall effect) and microscopic spectroscopic techniques (such as spin-resolved photoemission spectroscopy) report evidence of altermagnetic spin splitting , other experimental works report an absence of the effect , leaving the true magnetic ground state of the material an open question requiring further clarification.

— Multiconfigurational Analysis of Local Electronic Structure of $\mathrm{RuO_2}$ Using Relativistic Embedded Clusters  (2609.20526 - A. et al., 17 Sep 2026) in Section 1, Introduction

First-principles studies on prototype RuO$_2$ predicted strongly anisotropic anomalous Hall, Nernst, and thermal Hall responses, although its exact ground state and altermagnetic splitting remain actively debated.

— Cross-Layer Anomalous Hall Transport driven by Néel-Vector rotating in the Altermagnet candidate V2Te2O  (2609.05085 - Pan et al., 4 Sep 2026) in Introduction