Researchers have uncovered a straightforward explanation for unusual magnetoresistance in spintronics, challenging the dominant spin Hall magnetoresistance theory. The effect stems from electron scattering at material interfaces influenced by magnetization and electric fields. This discovery, detailed in recent experiments, offers a unified model without relying on spin currents.
Unusual magnetoresistance (UMR) has long puzzled scientists in the field of spintronics. This effect causes electrical resistance in heavy metals to change when placed adjacent to magnetic insulators, particularly as magnetization rotates perpendicular to the current flow. For years, spin Hall magnetoresistance (SMR) served as the primary explanation, influencing interpretations of various experiments including magnetoresistance measurements and spin-torque ferromagnetic resonance studies. However, UMR appeared in numerous systems where SMR should not apply, such as those lacking spin Hall materials, prompting alternative theories like Rashba-Edelstein MR and orbital Hall MR to explain the observations in specific setups. Prof. Lijun Zhu from the Institute of Semiconductors at the Chinese Academy of Sciences, along with Prof. Xiangrong Wang from the Chinese University of Hong Kong and co-author Qianbiao Liu, conducted experiments that point to a different mechanism: two-vector magnetoresistance. This model describes how electrons scatter at interfaces under the combined effects of magnetization and an electric field, independent of spin currents. Their findings show large UMR signals in single-layer magnetic metals, including higher-order contributions that follow a universal sum rule, aligning precisely with the two-vector MR predictions. Upon reanalyzing prior studies, the team found that many results previously linked to SMR or other spin-current mechanisms can be consistently interpreted through the two-vector framework. Several experimental and theoretical observations that contradicted spin-current models are naturally accounted for by this approach. Published in National Science Review in 2025 (volume 12, issue 8, DOI: 10.1093/nsr/nwaf240), the paper titled 'Physics origin of universal unusual magnetoresistance' provides strong experimental confirmation of this simpler explanation, potentially reshaping understanding of magnetoresistance in diverse spintronic systems.
