Carnegie Mellon Physicists Overturn Century-Old Hall Effect Assumption

Researchers at Carnegie Mellon University have identified an unusual magnetic response that overturns a long-standing assumption about the Hall effect, a foundational principle for studying materials' electrical and magnetic behavior. The findings, published in the journal Nature Materials, could eventually support simpler, more flexible magnetic sensors for electronics, transportation and medical imaging.

In 1879, physicist Edwin Hall discovered that a magnetic field applied perpendicular to a current-carrying material pushes its moving charges to one side, creating a measurable voltage that reveals whether current is carried by positive or negative charges, how many charge carriers are present, and how easily they move. Such sensors are now used in technologies from cars to computer keyboards, but for more than a century the effect was thought to require a perpendicular magnetic field.

Physicist Simranjeet Singh and colleagues at Carnegie Mellon's Lab for Investigating Quantum Materials, Interfaces and Devices (LIQUID) have now shown a Hall response can also appear when the magnetic field lies in-plane, an effect long predicted in theory but never demonstrated experimentally before this work. "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," Singh said.

With physicist Jyoti Katoch and postdoctoral researchers I-Hsuan Kao and Ravi Kumar, the team built devices from tantalum iridium telluride (TaIrTe4) reduced to a few atomic layers and placed next to a magnetic layer of chromium germanium telluride (Cr2Ge2Te6). The nearby magnetic layer gave the nonmagnetic TaIrTe4 magnetic properties while keeping its electronic characteristics, letting a single ultrathin device detect fields along more than one axis instead of separate sensors for each direction.

The LIQUID team is now testing other material combinations that could produce the same Hall response, and evaluating room-temperature behavior, a requirement for practical applications.