US team finds true source of magnetic effect in 'altermagnetic material'

Researchers at the U.S. Naval Research Laboratory (NRL) have identified the true source of a magnetic effect observed in ruthenium dioxide (RuO₂), a material previously considered a candidate for the newly predicted class of "altermagnetic" materials. Altermagnets have attracted significant interest due to their potential to enable faster, more energy-efficient computing technologies, particularly in spintronics and high-speed electronics. Early experimental reports suggested that RuO₂ exhibited exchange bias—a shifted magnetic hysteresis loop when interfaced with ferromagnets like iron—often interpreted as evidence of intrinsic antiferromagnetic order and thus altermagnetism. However, by combining conventional magnetometry with advanced neutron scattering techniques at Oak Ridge National Laboratory, the NRL team demonstrated that the observed exchange bias in RuO₂ is not an intrinsic property of the material itself but rather arises from complex interactions at the interfaces between RuO₂ and ferromagnetic layers. Neutron methods, including polarized neutron reflectometry and