Researchers at Carnegie Mellon University have identified an unusual magnetic response that contradicts a fundamental assumption underlying the Hall effect, a principle used extensively since 1879 to study how materials interact with electrical and magnetic fields. The findings, published in Nature Materials, suggest that the Hall effect can occur in different orientations than previously believed, potentially leading to more efficient magnetic sensors across various applications including automotive, medical imaging, and consumer electronics.
Edwin Hall’s original discovery in 1879 established that when a magnetic field is applied perpendicular to a material carrying electric current, charge carriers are deflected to one side, creating a measurable voltage. This phenomenon has been instrumental in understanding material properties and identifying whether charge carriers are positive or negative. Hall effect sensors are now ubiquitous in modern technology, from vehicles to computer keyboards.
The Carnegie Mellon team, working in their Lab for Investigating Quantum Materials, Interfaces and Devices, demonstrated that Hall responses can occur when the magnetic field is positioned parallel to the material’s plane, contradicting the longstanding assumption that only perpendicular field orientations produce measurable effects. While theoretical predictions had suggested this in-plane anomalous Hall effect was possible, no experimental verification had been achieved until this work.
The research involved constructing atomically thin devices using tantalum iridium telluride paired with a magnetic layer called chromium germanium telluride. When placed adjacent to one another, the magnetic properties from one layer influence the other, enabling the researchers to detect both conventional and unconventional Hall signals. This configuration allows a single sensor to measure magnetic fields along multiple axes, eliminating the need for separate sensors in different orientations.
The researchers, including theoretical physicists who modeled the underlying mechanisms, identified how reduced symmetry at the interface between the two materials enables additional spin-orbit coupling. The team is now investigating other material combinations that could produce similar effects and testing device functionality at room temperature, a critical requirement for practical commercial applications.
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