Scientists at the Hebrew University of Jerusalem have overturned a long-standing belief about how light interacts with matter — it turns out the magnetic field component of light plays a significant, direct role, not just the electric field. New theoretical calculations applied to a commonly used crystal show that light’s magnetic field can cause up to 17% of the observable polarization rotation (the Faraday Effect) in visible wavelengths and as much as 70% in the infrared range. This fundamentally reshapes how physicists understand the light-matter interaction, and opens doors for new applications in spintronics, magnetic control by light, and quantum-computing technologies.
Sources: Science Alert, SciTech Daily
Key Takeaways
– Light’s magnetic field — previously thought negligible — actually exerts a strong torque on the spins of electrons in materials, contributing significantly to the Faraday Effect.
– In experiments and theoretical modeling using a crystal (Terbium-Gallium Garnet), the magnetic contribution accounts for roughly 17% of polarization rotation in visible wavelengths and up to 70% in the infrared — a much larger effect than expected.
– This discovery could transform optical and magnetic technologies, enabling more precise magnetic control via light and boosting prospects for spin-based data storage and quantum computing.
In-Depth
For nearly two centuries, physics has treated light’s electric field as the main actor in its interactions with matter. When light passes through a magnetized material and its polarization rotates — the classic Faraday Effect, first observed in the mid-1800s — that rotation was attributed to the electric component of light influencing the charges in atoms. The magnetic component of light, meanwhile, was considered a passive passenger: too weak to contribute meaningfully. Now researchers at the Hebrew University of Jerusalem have upended that assumption. Their work shows that light’s magnetic field can actively influence electron spins inside a material, producing a measurable—and unexpectedly large—effect on how light behaves.
By modeling the response of a crystal known as Terbium-Gallium Garnet (TGG), the researchers found that in visible light wavelengths, the magnetic field of the passing light accounts for about 17 percent of the rotation observed during the Faraday Effect. But the impact becomes much stronger in the infrared: there, the magnetic component could explain up to 70 percent of the rotation. That’s a game changer. It suggests that light doesn’t just tug on electric charges; it actually exerts torque on the magnetic spins of electrons — a form of interaction that had not been acknowledged as significant until now.
At the heart of this insight is a dynamic often ignored: while the electric field pushes against charges (electrons in atoms), the magnetic field of light — especially if it’s circularly polarized — can spin or twist the internal magnetic moments (spins) of those electrons. This spin-based interaction resembles how a static magnetic field would influence a magnetized material: it’s a torque, not a force. By combining experimental data with advanced calculations (using the Landau–Lifshitz–Gilbert equation to model spin dynamics), the team showed that this magnetic “twist” changes the polarization of passing light in a measurable way.
Why does this matter beyond basic physics? Because it potentially rewrites the textbook rulebook on light-matter interactions. Technologies that rely on controlling magnetism or optical properties — including data storage, spintronics, and even future quantum-computing platforms — may now exploit this magnetic channel. Instead of relying solely on electric-field interactions or bulky magnets, engineers might use light itself, tuned carefully in polarization and wavelength, to flip spins, store information, or even control magnetic states remotely and rapidly.
Moreover, this discovery serves as a powerful reminder that even in well-established fields, long-standing assumptions can hide overlooked physics. It raises the possibility that other “small” effects we’ve ignored might turn out to be major players. As researchers explore these magnetic interactions of light further, we may see a wave of innovation — new materials, new devices, and even a rethinking of foundational optical theory.