A Long-Standing Spintronics Mystery May Finally Be Solved

A new experimental framework suggests that unusual magnetoresistance arises from interfacial electron scattering rather than spin currents, reshaping how magnetoresistance is understood across spintronic systems. Credit: SciTechDaily.com

A long-standing explanation for magnetoresistance may be incomplete. New evidence suggests a universal interfacial mechanism is at play.

A major advance in spintronics came with the discovery of unusual magnetoresistance (UMR). In this effect, the electrical resistance of a heavy metal changes when it is placed next to a magnetic insulator and the magnetization rotates within a plane that is perpendicular to the direction of the electric current.

This observation motivated the introduction of spin Hall magnetoresistance (SMR), a framework that quickly became widely accepted. SMR has since been used to explain UMR across many experimental settings, including standard magnetoresistance tests, spin-torque ferromagnetic resonance experiments, harmonic Hall voltage measurements, magnetic field sensors, and techniques for controlling magnetization or Néel-vector switching.

Over time, however, experiments revealed a broader and more puzzling picture. UMR was found to occur in many magnetic systems, even when no spin Hall material was present. Because the effect also appears in systems where SMR cannot apply (e.g., those without a spin Hall effect), researchers proposed a variety of alternative spin-current-related magnetoresistance (MR) models.

These include Rashba-Edelstein MR, spin-orbit MR, anomalous Hall MR, orbital Hall MR, crystal-symmetry MR, orbital Rashba-Edelstein MR, and Hanle MR, all aimed at explaining the “SMR-like” signals seen in specific materials.

Experimental Evidence for a New Mechanism

More recently, Prof. Lijun Zhu from the Institute of Semiconductors, Chinese Academy of Sciences, working with Prof. Xiangrong Wang from the Chinese University of Hong Kong, reported clear experimental results pointing to a different origin of universal UMR. Their work shows that the effect arises from electron scattering at material interfaces, controlled by the magnetization and the interfacial electric field.

This process is known as two-vector magnetoresistance and does not rely on spin currents.

Their experiments further reveal that extremely large UMR can appear even in single-layer magnetic metals. The measurements also show higher-order effects and follow a universal sum rule, all of which closely match the predictions of the two-vector MR model. Importantly, these results are obtained without the need to invoke spin-current-based mechanisms.

Reinterpreting Decades of Experimental Results

A systematic re-examination of existing literature further reveals that the most representative experimental data previously attributed to spin Hall magnetoresistance or other spin-current-related (or even unrelated) mechanisms can, in fact, be consistently explained within the framework of the two-vector MR theory. Moreover, they summarize a range of experimental and theoretical findings that strongly contradict spin-current-based MR models but are naturally accounted for by the two-vector MR mechanism.

These findings fundamentally challenge the long-standing and widely accepted SMR theory, offering the first robust experimental validation of the two-vector magnetoresistance model. By establishing a unified and universal physical origin for UMR, this work provides a simple yet comprehensive framework for understanding magnetoresistance phenomena in a broad range of spintronic systems.

Reference: “Physics origin of universal unusual magnetoresistance” by Lijun Zhu, Qianbiao Liu and Xiangrong Wang, 11 June 2025, National Science Review.

DOI: 10.1093/nsr/nwaf240

Never miss a breakthrough: Join the SciTechDaily newsletter.

Follow us on Google and Google News.