In 1879, Edwin Hall noticed that a magnetic field perpendicular to the current in a conductor produces a transverse voltage. For more than a century it was believed that the effect works only in that position — with the field strictly perpendicular to the plane of the sample. Scientists from Carnegie Mellon University have proved otherwise.
The researchers created an ultrathin heterostructure of several atomic layers of tantalum-iridium-telluride and magnetic chromium-germanium-telluride. Thanks to the precise matching of the crystal symmetries and the close contact between the layers, the magnetism from the second material penetrated into the first without destroying its electronic properties.
In such devices the scientists registered not only the familiar Hall signal but also a second, unusual response that depends on the magnetisation in the plane of the material. This means that a single miniature sensor is now capable of measuring the magnetic field along two axes at once.
Previously, vector magnetometry required two separate sensors. The new architecture simplifies the design and opens the way to more compact devices in electronics, transport and medical diagnostics.
Theoretical modelling showed that at the boundary between the layers an additional spin-orbit interaction arises, and it is this that permits the previously "forbidden" response. The experiment confirmed the predictions, although the exact mechanism is still being refined.
The team is already searching for other combinations of materials and testing how the devices perform at room temperature. If the result proves stable, single-crystal multidimensional Hall sensors could appear in everyday technology within the next few years.
A single tiny device is now capable of replacing several previous sensors.
