For nearly two centuries, the Faraday Effect—where the polarization of light rotates as it travels through a magnetized material—has been explained almost entirely through the interaction between light’s electric field and the material’s electrons. But new research from The Hebrew University of Jerusalem shows that the magnetic component of light itself contributes significantly to the effect—sometimes contributing more than the electric field at certain wavelengths.
The study, led by Benjamin Assouline and Dr. Amir Capua, presents an analytical and numerical model showing that the oscillating magnetic field of light exerts a measurable magnetic torque on the spins inside a material. This challenges a long-standing assumption in magneto-optics and introduces a new physical mechanism behind one of photonics’ most fundamental phenomena.
Using terbium gallium garnet (TGG)—a workhorse material for optical isolators, rotators, and other photonic components—the researchers found that at an ~800 nm wavelength, the magnetic component explains roughly 17% of the material’s rotation response. At 1.3 µm, widely used in telecom and infrared photonics, the contribution jumps to nearly 70%, meaning the magnetic field of light may dominate the behavior engineers observe.
The findings could have meaningful implications for the design of optical isolators, magneto-optic sensors, high-power laser components, and integrated photonics platforms. Devices operating in infrared bands may require new material models, new rotation constants, and new device-optimization strategies that include magnetic-field coupling—not just electric-field effects.
The researchers emphasize that this work provides the theoretical foundation; experimental validation across materials and wavelengths will follow. But for engineers designing next-generation photonics, this expanded understanding opens new design space in magneto-optical behavior and materials engineering.
Original Research:
Assouline, B. & Capua, A. Faraday effects emerging from the optical magnetic field. Scientific Reports (2025). https://www.nature.com/articles/s41598-025-24492-9
