An atomic force microscopy scan of a nanometer-sized device developed by Carnegie Mellon scientists demonstrating a new form of the Hall effect. For more than a century, the Hall effect has been taught with a simple picture of electricity flowing through a material, a magnetic field pushing moving charges sideways, and a voltage appearing across the material. Now, scientists have found a way to make that familiar phenomenon work in a direction previously thought impossible. According to a report in Science Daily, researchers at Carnegie Mellon University have demonstrated an unusual form of the Hall effect in which a magnetic field located within the plane of a material can produce a measurable Hall response. The discovery, published in Nature Materials, challenges a long-standing assumption in condensed matter physics and could eventually lead to simpler magnetic sensors capable of detecting fields in multiple directions. According to the online report, Edwin Hall discovered the Hall effect in 1879. In the conventional setup, a magnetic field is applied perpendicular to a material that carries an electric current. The field deflects moving charges, creating a voltage that can be measured throughout the material. That voltage can reveal valuable information about the material, including the type and concentration of the charge carriers and the ease with which they move. Since then, the principle has become part of everyday technology. Hall effect sensors are used in applications ranging from automobiles and keyboards to industrial electronics. But Carnegie Mellon researchers working at the Laboratory for Research in Quantum Materials, Interfaces and Devices (LIQUID) have now shown that the answer doesn’t have to be limited to traditional geometry. Turning a theoretical prediction into reality Scientists had previously predicted an in-plane anomalous Hall effect, but proving it experimentally proved difficult. The challenge was to find a material system with exactly the right symmetry. The team started with tantalum-iridium telluride (TaIrTe₄), a two-dimensional quantum material whose crystalline structure can support this unusual response. The researchers reduced it to a few atomic layers and placed it next to a magnetic material called chromium germanium telluride (Cr₂Ge₂Te₆), or CGT. Because the two layers are extremely close together, the magnetic layer transfers its influence to the normally non-magnetic TaIrTe₄. The result is an atomically thin device with specially designed electronic and magnetic properties. One device, multiple magnetic directions Within the resulting structure, the researchers detected the familiar Hall signal, as well as a second unconventional signal associated with magnetization found within the plane of the material. This could have important implications for magnetic sensing. Instead of requiring separate sensors to measure magnetic fields along different axes, a single ultra-thin device could detect multiple directions. The researchers say this could enable new forms of vector magnetometry, with applications in electronics, transportation and medical imaging. Why this unusual effect appears The experimental work was accompanied by theoretical models to understand the physics behind the discovery. The researchers found that combining the two materials reduces the symmetry of the system and allows additional spin-orbit coupling at its interface. These interactions become important when the CGT becomes ferromagnetic at low temperatures, which helps produce the anomalous in-plane Hall response. However, the precise microscopic mechanism is not yet fully established and further characterization of the few-layer TaIrTe₄ is needed. What comes next? The Carnegie Mellon team is now looking for other combinations of two-dimensional materials that could produce the same effect. Another important objective is to determine if the devices can operate at room temperature. That step will be crucial for any practical technology. For now, the discovery expands the possibilities of a phenomenon first identified nearly 150 years ago, showing that even one of the most familiar effects in physics can still have some hidden surprises. Image credit: Carnegie Mellon and Wikipedia
