Researchers at Carnegie Mellon University have made a groundbreaking discovery that could transform the way we understand and utilize the Hall effect, a fundamental principle in electronic materials. This new insight reveals an unexpected phenomenon that challenges existing beliefs about how electronic materials interact with magnetic fields.
Documented in Nature Materials, the study holds potential for advancing the development of more versatile and streamlined magnetic sensing technologies across various fields, including electronics, transportation, and medical imaging.
The Hall effect, introduced by Edwin Hall in 1879, has long served as a crucial tool for analyzing material properties by examining how a magnetic field influences moving charges in a material. By assessing the resulting voltage, scientists can determine key characteristics of the electric current. This effect is foundational to many technologies, from automotive systems to computer keyboards.
The latest research from Carnegie Mellon’s Department of Physics and the Lab for Investigating Quantum Materials, Interfaces and Devices (LIQUID) introduces a novel form of the Hall effect. According to Simranjeet Singh, an associate professor of physics, “For a long time, people thought the Hall effect only worked when the magnetic field was applied perpendicular to the plane of the film. We’ve shown that that’s not true — you can also get a response when the field is in-plane.”
This finding expands the Hall effect’s applicability, enabling magnetization-dependent responses in multiple directions. As Singh notes, this advancement can lead to innovative device architectures and sensor types, such as vector magnetometry, by measuring both out-of-plane and in-plane anomalous Hall effect signals within a single device.
From Theory to Practice
The concept of an in-plane anomalous Hall effect has been theoretically discussed but never empirically validated until now. Singh states, “People proposed it and ideas were out there, but it’s very difficult to make a magnetic material with the right symmetry to do it.” The breakthrough came when the team identified a material with suitable symmetry and induced magnetism in it.
Singh collaborated with Jyoti Katoch, an associate professor of physics experienced in creating devices from two-dimensional quantum materials. The research team, including postdoctoral researchers I-Hsuan Kao and Ravi Kumar, utilized tantalum iridium telluride (TaIrTe4), which possesses the necessary crystalline symmetry for a multidimensional Hall effect, and combined it with a magnetic layer, Cr2Ge2Te6 (CGT).
The close proximity of these layers allows magnetism to penetrate the nonmagnetic layer, endowing it with magnetic properties while preserving its electronic characteristics. Katoch highlights the significance of these developments, stating, “This truly demonstrates the power of building atomically precise heterostructures of emergent two-dimensional quantum materials to obtain on-demand electronic and magnetic properties.”
In these ultrathin devices, both conventional and unconventional Hall signals were observed, enabling the detection of magnetic fields along multiple axes. As Singh explains, “You can do multidimensional magnetic sensing with one sensor only. Before you needed to put two sensors to measure the magnetic field in two directions.”
Complementing the experimental work, Shubhayu Chatterjee, an assistant professor of physics, conducted theoretical modeling to elucidate the mechanism behind the effect. “We found that the reduced symmetry due to pairing with CGT allows additional spin-orbit coupling at the interface,” Chatterjee explained. This spin-orbit coupling is vital for the in-plane anomalous Hall effect to manifest when CGT becomes ferromagnetic at low temperatures.
Currently, the LIQUID team is investigating other materials that might exhibit similar unconventional Hall responses, as well as testing the device’s performance at room temperature, a key step towards practical applications.
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