Researchers identify light’s hidden magnetism in Faraday Effect
24 Nov 2025
Researchers at the Hebrew University of Jerusalem claim they have overturned a nearly two centuries old assumption about the relationship between electromagnetism and light.
The Faraday Effect, a cornerstone of modern physics first described in 1845 by Michael Faraday, describes the effect by which a magnetic field causes the polarisation plane of light travelling through material to rotate.
Traditionally, the effect has been ascribed to the electric field of light and the electric charges in matter interacting.
The new research published in Nature’s Scientific Reports suggests that the previously ignored role of the magnetic field of light is itself a contributor to the process.
“What we’ve found is that the magnetic part of light has a first-order effect, it’s surprisingly active in this process,” explained Dr Amir Capua from the university’s Institute of Electrical Engineering and Applied Physics.
Using the Landau–Lifshitz–Gilbert (LLG) equation, describing the motion of spins in magnetic systems, the scientists produced calculations to demonstrate the magnetic field of light also generates a magnetic torque inside the material.
Applying the model to the crystal routinely use to measure the Faraday Effect, Terbium Gallium Garnet (TGG), they surmised that the magnetic field of light accounted for about 17% of the observed rotation at visible wavelengths and up to 70% in the infrared range.
“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,” said Capua’s colleague Benjamin Assouline.
The study concludes that the evidence offered potential developments in magnetism, optics and possibly even spin-based quantum computing technology development.
Pic: Enrique Sahagún
