Scientists at the Hebrew University in Jerusalem, Israel, say a 180-degree theory about light was wrong this whole time and offer an update. This discovery could help advance technological areas such as sensing, computer memory and quantum computing.
Described in 1845 by the British physicist Michael Faraday, the Faraday effect is a theory linked to the interaction between magnetism and light waves. According to her, when you use polarized light and pass it through a magnetic field, the direction of the polarization changes. This type of light is like the aligned fibers of a sweater – and the effect works by “twisting” the fibers.
According to Faraday’s ideas, in this process the external magnetic field acted on the material and the electric field of light responded to the change, while its own magnetic field was weak and had practically no influence.
Israeli scientists, however, disagree with this 180-year-old theory. According to them, the magnetic field of light also influences the Faraday effect – with a significant contribution. The results were published in the scientific journal Scientific Reports on November 19.
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The starting point for “tweaking” this effect took place in 2024. By carrying out an experiment in which light influenced the magnetism of the material, the researchers wondered whether the same thing could happen in the nearly two centuries old theory.
In search of answers, they combined the results of the previous discovery with calculations based on the Landau-Lifshitz-Gilbert equation, which helps describe the magnetism of solid materials. As a basis, they used physical models of terbium-gallium garnet, a magnetizable crystal widely used in fiber optics and other telecommunications applications.
Reportedly, the magnetic field of light contributes about 17% of the Faraday effect in visible wavelengths and 70% in infrared wavelengths, showing a much more significant influence than previously imagined. In other words, the results show that both light fields influence the theory, the electric and the magnetic.
“Light not only illuminates matter, but it also influences it magnetically. The static magnetic field “twists” the light and this, in turn, reveals the magnetic properties of the material. What we discovered is that the magnetic part of light has a first-order effect, being surprisingly active in this process,” explained the co-author of the article, Amir Capua, in an interview with the Science Alert portal.
The influence was only seen through the spin of the electrons, since the magnetic field of the light did not interact directly with the particle, but rather with this fundamental property of the electron. Capua points out that spins are like a small charge rotating around its own axis, as if it were a very small vertex and forces can make it rotate or change direction, as in this case.
In practice, in addition to “rewriting” the Faraday effect, this discovery could help advance important technological areas.
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