Image Courtesy: Carnegie Mellon
Carnegie Mellon University researchers have demonstrated an unusual form of the Hall effect that challenges a long-standing assumption about how the phenomenon responds to magnetic fields. The finding could expand how scientists study magnetic materials and eventually lead to simpler sensors capable of detecting magnetic fields in multiple directions.
The Hall effect has been a fundamental tool in physics since Edwin Hall discovered it in 1879. When a magnetic field is applied perpendicular to a material carrying an electric current, the moving charges are deflected to one side, creating a measurable voltage. That signal can reveal properties such as the type and concentration of charge carriers and how easily they move. Hall sensors are now used in everything from automobiles to computer keyboards.
Researchers from Carnegie Mellon’s Department of Physics have now shown that a related anomalous Hall response can also occur when the magnetic field lies within the plane of a material.
“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 phenomenon had been predicted theoretically, but demonstrating it experimentally required a material with the right symmetry. Singh’s team began with tantalum iridium telluride (TaIrTe4), a two-dimensional quantum material, and reduced it to just a few atomic layers. The researchers then combined it with a magnetic material called chromium germanium telluride (Cr2Ge2Te6), or CGT.
The close proximity between the two layers transferred magnetic properties to the normally nonmagnetic TaIrTe4 while preserving much of its underlying electronic behavior. The resulting nanoscale device produced both the conventional Hall signal and an additional response associated with magnetization within the plane.
The researchers say this could allow a single ultrathin device to measure magnetic fields along multiple axes. “You can do multidimensional magnetic sensing with one sensor only,” Singh said, noting that conventional approaches can require separate sensors to measure fields in different directions.
Theoretical work by Shubhayu Chatterjee, an assistant professor of physics, suggests that the interface between the two materials reduces the system’s symmetry and enables additional spin-orbit coupling. These interactions appear to be important for producing the in-plane anomalous Hall effect, although the researchers say more characterization is needed to establish the precise mechanism.
The team is now testing other material combinations and investigating whether the effect can operate at room temperature, a key step toward practical applications in electronics, transportation and medical imaging.
