Spin‐Orbit Coupling Driven Magnetic Response in Altermagnetic RuO ₂

The recent prediction of the new magnetic class, altermagnetism, has drawn considerable interest, fueled by its potential to host novel phenomena and to be utilized in next-generation spintronics devices. Among many promising candidates, rutile RuO₂ is a prototypical candidate for realizing the prospects of altermagnetism. However, the experimental studies on RuO₂ are still in the early stages. In this study, the magnetic responses in RuO₂ film are investigated by the Planar Hall effect (PHE). By rotating the external field (H_ext), the PHE exhibits twofold behaviors. Moreover, the planar Hall conductivity shows a nonlinear response to the H_ext. These observed features in PHE resemble those in ferromagnet and topologically nontrivial systems, suggesting the field-induced magnetic response in rutile antiferromagnet. The work provides a strategy for detecting intriguing magnetic responses in altermagnetic materials, promoting further research in altermagnet-based spintronics and novel phenomena.