Absence of altermagnetic order in RuO₂

As the search for materials that meet the requirements of altermagnetic order continues to grow, RuO₂ is in the spotlight as a prototypical candidate. However, its magnetic properties are still controversial, with several experiments classifying it as a paramagnet while others reporting altermagnetic order. In this talk, we will present first principles-based modelling and discuss recent experimental results (muon spin spectroscopy, neutron diffraction) that show a lack of magnetic order in the pristine RuO₂ structure [1,2]. Furthermore, we will provide an explanation, using first principles-based calculations of the Anomalous Hall Effect recently observed in Cr-doped RuO₂, with the extra holes introduced by Cr being bound to the Cr impurity and not the Ru bands.

Part of this work has been done in collaboration with Philipp Keßler, Andreas Suter, Thomas Prokscha, Zaher Salman, Dmitry Khalyavin, Pascal Manuel, Fabio Orlandi and Simon Moser.