Investigation of magnetic ordering in RuO₂ via polar Kerr effect

The magnetic ordering of RuO₂ has been a recent topic of debate due to its emergence as a candidate for a model altermagnet and contrasting experimental observations ranging from paramagnetism to high temperature antiferromagnetism to the absence of magnetic order. Theoretical calculations suggest that stoichiometric RuO₂ is likely nonmagnetic, though hole doping could induce magnetism, indicating that magnetism could vary from sample to sample and depend on the growth conditions. Current experimental data does not provide a definitive conclusion on the magnetic structure of RuO₂, and further measurements are needed. We performed polar Kerr effect measurements on both bulk RuO₂ and thin films from multiple sources and with multiple crystallographic orientations and thickness, over a temperature range of 2 K to 475 K. Our results aim to provide additional data toward characterizing the magnetic structure of RuO₂ and help resolve the ongoing debate.