Carnegie Mellon University researchers have identified an unusual magnetic response that overturns a long-standing assumption about the Hall effect, a foundational principle used to study how materials behave electrically and magnetically. The findings, published in Nature Materials, expand scientists' understanding of the Hall effect and could eventually support simpler and more flexible magnetic sensors for electronics, transportation and medical imaging. Scientists have relied on the Hall effect for more than a century.
In 1879, Edwin Hall discovered that when a magnetic field is applied perpendicular to a material carrying an electric current, the moving charges are pushed to one side. This creates a voltage that researchers can measure. That signal reveals important information about a material, including whether its current is carried by positive or negative charges, how many charge carriers are present, and how easily they can move.
Hall effect sensors are now widely used in technologies ranging from cars to computer keyboards. Researchers in Carnegie Mellon's Department of Physics, working in the Lab for Investigating Quantum Materials, Interfaces and Devices (LIQUID), have now demonstrated a different form of the effect. "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," said Simranjeet Singh, an associate professor of physics. The result shows that a Hall response tied to magnetization can occur in more than one direction. That gives physicists a new way to investigate multidimensional magnetic and topological structures in condensed matter systems.
"Beyond fundamental importance, this discovery can enable novel planar device architectures and sensor types, such as vector magnetometry, via measuring the out-of-plane and in-plane anomalous Hall effect signals in the same device," Singh said. Scientists had previously predicted an in-plane anomalous Hall effect in theory, but no experiment had successfully demonstrated it before this work. "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," Singh said.
"What we did was we found a material with the right symmetry, and we made it magnetic." Creating the nanometer-sized devices required for the experiment involved expertise in two-dimensional quantum materials. Singh worked with Jyoti Katoch, an associate professor of physics who specializes in fabricating devices from such materials. The research team, which included postdoctoral researchers I-Hsuan Kao and Ravi Kumar, began with tantalum iridium telluride (TaIrTe4).
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