Determining the Nature of Magnetism in Altermagnetic Candidate RuO
arXiv:2504.21138
Abstract
The terminology "altermagnetism" has recently been adopted to describe collinear magnetic order with no net magnetization and non-relativisitic, momentum-dependent spin-splitting. The archetypal material used to theoretically explore altermagnetism is RuO, but there has been significant debate as to whether RuO possesses magnetic, let alone altermagnetic, order. To address questions surrounding the nature of magnetism in RuO, we combine symmetry-sensitive torque magnetometry and magnetization measurements in single crystals. The data are inconsistent with collinear magnetic order possessing a Néel vector along the axis. Torque magnetometry further demonstrates an isotropic magnetic susceptibility within the plane, indicative of neither a Néel vector within the plane nor a field-induced Néel vector reorientation. Magnetic quantum oscillations from both techniques reveal a nearly spherical Fermi surface pocket at the Brillouin zone center, in agreement with paramagnetic electronic structure calculations. Taken together, these data indicate no detectable long-range magnetic order and, by extension, suggest no altermagnetism in high-quality RuO single crystals.
7 pages, 4 figures