Light's hidden magnetic power rewrites 180 years of physics

For nearly two centuries, physicists thought they understood how light bends through magnetic fields. They were only half right.

Researchers at Hebrew University of Jerusalem have discovered that light's magnetic component—long dismissed as negligible—actually plays a direct and measurable role in the Faraday Effect, the phenomenon where light's polarization rotates as it passes through a magnetized material. The finding overturns a foundational assumption that only light's electric field mattered in this interaction.

"In simple terms, it's an interaction between light and magnetism," explains Dr. Amir Capua, who led the study published in Nature's Scientific Reports. "The static magnetic field 'twists' the light, and the light, in turn, reveals the magnetic properties of the material. What we've found is that the magnetic part of light has a first-order effect—it's surprisingly active in this process."

The team, working with Benjamin Assouline at the Institute of Electrical Engineering and Applied Physics, used advanced calculations based on the Landau-Lifshitz-Gilbert equation—a tool that describes how atomic spins behave in magnetic materials—to show that light's oscillating magnetic field interacts directly with those spins. This wasn't a small correction. When they tested their model on Terbium Gallium Garnet, a crystal commonly used to study these effects, the magnetic component of light accounted for roughly 17% of the observed rotation in visible light and up to 70% in infrared wavelengths.

Why does this matter now, after 180 years. Because it changes how we think about light as a tool. "Light doesn't just illuminate matter, it magnetically influences it," Capua says. That distinction opens practical doors: optical data storage systems could become more efficient, spintronics—the field that manipulates electron spin for computing—gains a new lever to pull, and the emerging frontier of spin-based quantum computing suddenly has another mechanism to work with.

The insight is particularly striking because it reveals something fundamental about light we've been overlooking. Every photon carries both an electric and magnetic field, locked together in an oscillating dance. Scientists had assumed the magnetic side was a passenger in the Faraday Effect. The new work shows it's a co-pilot.

This kind of revision—where a century-old framework turns out to be incomplete rather than wrong—is how science deepens. The electric field explanation still holds. It's just that the full picture was always bigger than we thought.