Science uncovers a 150-year-old hidden side of two most precious things to us

A group of scientists has found a way to spot very faint magnetic signals in everyday metals like copper, gold, and aluminum, using only light and a refined technique. Their study, published in Nature Communications, shows how something once thought invisible can now be measured.

The Hall effect, discovered nearly 150 years ago, explains how electric currents bend when exposed to a magnetic field. In magnetic materials such as iron, this effect is strong. In non-magnetic metals, however, the effect is much weaker. A related idea, the optical Hall effect, was expected to exist but was too subtle to detect with visible light.

“It was like trying to hear a whisper in a noisy room for decades,” said Prof. Amir Capua of Hebrew University. “Everyone knew the whisper was there, but we didn’t have a microphone sensitive enough to hear it.”

The team, led by Ph.D. candidate Nadav Am Shalom and Prof. Capua, worked with colleagues from the Weizmann Institute of Science, Pennsylvania State University, and the University of Manchester. They focused on how to measure these tiny magnetic effects in metals that do not behave like magnets in daily life.

“You might think of metals like copper and gold as magnetically ‘quiet’—they don’t stick to your fridge like iron does,” explained Prof. Capua. “But in reality, under the right conditions, they do respond to magnetic fields—just in extremely subtle ways.”

To make this possible, the researchers improved a method called the magneto-optical Kerr effect (MOKE). This technique uses a laser to see how magnetism changes the reflection of light. By using a 440-nanometer blue laser and strongly modulating the external magnetic field, they boosted sensitivity enough to detect signals in copper, gold, aluminum, tantalum, and platinum.

The team pointed out that the anomalous Hall effect in ferromagnets is much stronger than the ordinary Hall effect, which makes the optical Hall effect even weaker than MOKE. That is why it has been so hard to detect at visible wavelengths. Their upgraded MOKE method finally overcame this barrier.

The results partly matched the Lorentz-Drude theory, which describes how electrons respond to electromagnetic fields. But the data also showed contributions from plasma dynamics and interband transitions, meaning the behavior was more complex than the theory alone could explain.

Another surprising finding was that the “noise” in their measurements was not random. Instead, it scaled with the spin-orbit coupling of the metals, a property that links how electrons move with how they spin. This was tied to Gilbert damping enhancement, which describes how magnetic energy fades in materials. The researchers concluded that the noise came from optical interactions with spins, mediated by spin-orbit coupling.

“It’s like discovering that static on a radio isn’t just interference—it’s someone whispering valuable information,” said Am Shalom. “We’re now using light to ‘listen’ to these hidden messages from electrons.”

The new method avoids the need to attach wires to devices, which is difficult at very small scales. Instead, it only requires shining a laser, making it simpler and less invasive.

The implications are broad, from magnetic memory and spintronics to quantum computing. Because the technique does not require extreme cooling or very large magnets, it could be used more widely in engineering and materials science.

“This research turns a nearly 150-year-old scientific problem into a new opportunity,” said Prof. Capua. He recalled that Edwin Hall, who discovered the Hall effect in 1881, had tried to measure it with light but failed. Hall wrote: “I think that, if the action of silver had been one tenth as strong as that of iron, the effect would have been detected. No such effect was observed.”

By tuning their system to the right frequency, the team has now achieved what Hall could not, opening a new way to study how electrons behave in metals once thought magnetically silent.

Source: Hebrew University of Jerusalem, Nature

This article was generated with some help from AI and reviewed by an editor. Under Section 107 of the Copyright Act 1976, this material is used for the purpose of news reporting. Fair use is a use permitted by copyright statute that might otherwise be infringing.

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Posted Saturday 14 March 2026 at 11:02 am AEST (my time).

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