An anomalous Hall effect in altermagnetic ruthenium dioxide

The anomalous Hall effect is a time-reversal symmetry-breaking magneto-electronic phenomenon originally discovered in ferromagnets. Recently, ruthenium dioxide (RuO₂) with a compensated antiparallel magnetic order has been predicted to generate an anomalous Hall effect of comparable strength to ferromagnets. The phenomenon arises from an altermagnetic phase of RuO₂ with a characteristic alternating spin polarization in both real-space crystal structure and momentum-space band structure. Here we report an anomalous Hall effect in RuO₂ with an anomalous Hall conductivity exceeding 1,000 Ω⁻¹ cm⁻¹. We combine the vector magnetometry and magneto-transport measurements of epitaxial RuO₂ films of different crystallographic orientations. We show that the anomalous Hall effect dominates over an ordinary Hall contribution, and a contribution due to a weak field-induced magnetization. Our results could lead to the exploration of topological Berry phases and dissipationless quantum transport in crystals of abundant elements and with a compensated antiparallel magnetic order.