Scientists at the Hebrew University of Jerusalem have discovered that the magnetic field of light plays a significant role in the Faraday Effect, challenging nearly 200 years of scientific understanding. Their findings show that this magnetic component contributes directly to how light interacts with materials. The research opens potential advances in optics and spintronics.
For almost two centuries, the Faraday Effect—where the polarization of light rotates as it passes through a material in a magnetic field—has been explained solely by light's electric field interacting with electric charges in matter. A new study led by Dr. Amir Capua and Benjamin Assouline from the Hebrew University of Jerusalem's Institute of Electrical Engineering and Applied Physics overturns this view. Published in Scientific Reports on November 20, 2025, the research demonstrates that light's oscillating magnetic field also exerts a direct influence by interacting with atomic spins.
The team used advanced calculations based on the Landau-Lifshitz-Gilbert equation, which models spin behavior in magnetic materials, to quantify this effect. They applied their model to Terbium Gallium Garnet (TGG), a common crystal for studying the Faraday Effect. Results indicate the magnetic component accounts for about 17% of the rotation in the visible spectrum and up to 70% in the infrared.
"In simple terms, it's an interaction between light and magnetism," says Dr. Capua. "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."
Capua further explains, "In other words, light doesn't just illuminate matter, it magnetically influences it."
Benjamin Assouline adds, "Our results show that light 'talks' to matter not only through its electric field, but also through its magnetic field, a component that has been largely overlooked until now."
This revised understanding could pave the way for innovations in optical data storage, spintronics, and light-based magnetic control, potentially aiding spin-based quantum computing.