Japanese physicists have observed an elusive form of the “Hall effect” in a nonmagnetic material for the first time ever. The material, cadmium arsenide (Cd3As2), now proves theoretical predictions that “Anomalous Hall Effect” (AHE) can exist in nonmagnetic materials.
“Our study is the first to experimentally confirm that AHE can be quantitatively detected in nonmagnetic materials using in-plane magnetic fields,” said team lead and Associate Professor Masaki Uchida from the Tokyo Institute of Science and Technology.
For the uninitiated, the Hall effect, first discovered in 1879 by Edwin Hall, is a phenomenon where an electric current flowing through a conductor or semiconductor in the presence of a magnetic field produces a voltage across the material.
In magnetic materials, you can get a Hall-like voltage even without an external magnetic field. This happens because the material’s own magnetization (usually from electron spin) bends the motion of electrons.
Science is never settled
For decades, it was assumed that AHE was always spin-driven and only occurred in magnetic materials. However, the Japanese team has overturned this by observing a giant AHE in a nonmagnetic material.
Dirac semimetals, like cadmium arsenide, have special points in their band structure (Dirac points) where electrons behave like massless particles. Under certain conditions (like applying a magnetic field), these can split into Weyl points, changing electron motion dramatically.
To achieve this, the team grew very pure thin films of Cd₃As₂ using molecular beam epitaxy. Once in hand, they then applied a magnetic field in the plane of the film (not perpendicular, which is more typical).
The team also developed a way to distort the electronic band structure in a controlled way. This, the team explained, let them “filter out” the ordinary Hall effect and isolate the anomalous one.
Using this methodology, they were able to measure the Hall conductivity and saw a large AHE signal within the cadmium arsenideUsing this methodology, they were able to measure the Hall conductivity and saw a large AHE signal within the cadmium arsenide films.
The findings of the study are important as the AHE here didn’t come from spin magnetization (like in normal ferromagnets). Instead, it originated from orbital magnetization, which is the circular orbital motion of electrons themselves.
Opens new AHE possibilities
That’s significant because orbital contributions are often overlooked in AHE discussions. To this end, the study proves theoretical predictions that AHE can exist in nonmagnetic materials.
It also challenges the long-standing assumption that AHE was driven solely by spin. Looking ahead, the findings open up new directions for understanding electron orbital effects more effectively.
It could also open up opportunities for new technology. For example, new kinds of Hall sensors, spintronics, or electronic devices that don’t rely on magnetism but still exploit AHE (potentially smaller, faster, more versatile).
“We expect these results to catalyze both basic research into the underlying physics and applied research into devices that leverage the AHE,” explained Uchida.
“Hall sensors and other devices that exploit AHE in nonmagnetic materials could become more efficient and operate under broader conditions than current technologies,” he added.
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