Researchers discovered a significant anomalous Hall effect in the magnetic material SrCo6O11 at temperatures above its magnetic transition, where it exhibits a phenomenon known as the “Spin-Fluctuating Devil’s Staircase.” This observation could revolutionize the design of materials for magneto-thermoelectric conversion, impacting the development of new thermoelectric materials.
Here’s a bit of background: When an electric current flows through a metal sample in a magnetic field, it experiences the Lorentz force. This force generates a voltage perpendicular to the magnetic field and current—a phenomenon referred to as the Hall effect.
In magnetic metals, a similar phenomenon—known as the anomalous Hall effect—may occur independently of an external magnetic field, particularly in ferromagnetic materials wherein electron spins are aligned. Generally, this alignment—and thus the anomalous Hall effect—only manifests below a certain temperature, known as the magnetic transition temperature.
Above this temperature, the spins become disordered, leading to the near disappearance of the anomalous Hall effect. Although the anomalous Hall effect can occur above the magnetic transition temperature when spins are aligned by an external magnetic field in theory, it is usually exceedingly weak.
Observations in SrCo6O11
In this study, the researchers observed a large anomalous Hall effect at temperatures exceeding the magnetic transition temperature in the magnetic material SrCo6O11, which exhibits a unique magnetic transition phenomenon known as the “Spin-Fluctuating Devil’s Staircase.”
Notably, the magnitude of the anomalous Hall effect—or the anomalous Hall angle—was among the largest recorded for magnetic oxides. The research suggests that this significant effect likely stems from the intense scattering of conduction electrons due to a specific type of spin fluctuation known as spin-flip fluctuation.
This large anomalous Hall effect has significant implications for the principle of magneto-thermoelectric conversion. The findings of this study provide a new principle for designing materials for this technology, which could have a substantial impact on the development of new thermoelectric conversion materials.
Reference: “Large anomalous Hall effect in spin fluctuating devil’s staircase” by Naoki Abe, Yuya Hano, Hiroaki Ishizuka, Yusuke Kozuka, Terumasa Tadano, Yoshihiro Tsujimoto, Kazunari Yamaura, Shintaro Ishiwata and Jun Fujioka, 17 May 2024, npj Quantum Materials.
DOI: 10.1038/s41535-024-00653-3