Amazing stuff!
"Scientists have cracked a century-old physics mystery by detecting magnetic signals in non-magnetic metals using only light and a revamped laser technique. Previously undetectable, these faint magnetic “whispers” are now measurable, revealing hidden patterns of electron behavior. The breakthrough could revolutionize how we explore magnetism in everyday materials—without bulky instruments or wires—and may open new doors for quantum computing, memory storage, and advanced electronics. ...
For over a century, scientists have known that electric currents bend in a magnetic field—a phenomenon known as the Hall effect. In magnetic materials like iron, this effect is strong and well understood. But in ordinary, non-magnetic metals like copper or gold, the effect is much weaker.
In theory, a related phenomenon—the optical Hall effect—should help scientists visualize how electrons behave when light and magnetic fields interact. But at visible wavelengths, this effect has remained far too subtle to detect. ...
To solve this, the researchers upgraded a method called the magneto-optical Kerr effect (MOKE), which uses a laser to measure how magnetism alters light’s reflection. ...
By combining a 440-nanometer blue laser with large-amplitude modulation of the external magnetic field, they dramatically boosted the technique’s sensitivity. The result: they were able to pick up magnetic “echoes” in non-magnetic metals like copper, gold, aluminum, tantalum, and platinum—a feat previously considered near-impossible. ...
The technique offers a non-invasive, highly sensitive tool for exploring magnetism in metals—without the need for massive magnets or cryogenic conditions. Its simplicity and precision could help engineers build faster processors, more energy-efficient systems, and sensors with unprecedented accuracy. ..."
From the abstract:
"It is well known that the anomalous Hall effect displayed in ferromagnets is much stronger than the ordinary Hall effect. Therefore, the optical Hall effect is significantly weaker than the magneto-optical Kerr effect (MOKE) such that it is barely detectable at visible wavelengths.
We present a sensitive MOKE technique which is based on large-amplitude modulation of the externally applied magnetic field that is suitable for non-magnetic metals. Using a 440 nm laser, we measure Cu, Au, Al, Ta, and Pt and find partial agreement with the Lorentz-Drude theory implying contributions of the plasma dynamics and interband transitions beyond the approximations of the model.
Interestingly, we find that the noise scales with the spin-orbit coupling of the metals. This is manifested by a remarkable correlation between the noise amplitude and the Gilbert damping enhancement associated with these metals. These results suggest that the electromagnetic noise arises from optical interactions with spins that is mediated by the spin-orbit interaction and highlight a possible avenue for measuring the spin-orbit coupling using optical techniques."
A sensitive MOKE and optical Hall effect technique at visible wavelengths: insights into the Gilbert damping (open access)
Fig. 1: Schematic illustration of the OHE and the experimental setup.
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