The Reinterpretation of Light and Magnetism: Two Centuries in the Making

In 1845, physicist Michael Faraday provided groundbreaking evidence connecting electromagnetism and light. This relationship has proven to be stronger than Faraday initially anticipated.

During his experiment, Faraday directed light through a mixture of boric acid and lead oxide contained in a magnetic field. He noticed a shift in the light, with its polarization direction being altered upon exiting the glass.

For the last 180 years, it has been a widely held belief that light acts as an electromagnetic wave, with the “Faraday effect” illustrating how the interplay of the magnetic field, the charge within the glass, and the electric component of light causes a rotation and deviation in the direction of light waves once they leave the material.

Surprisingly, scholars have long assumed that the magnetic aspect of light has little impact on the Faraday effect. However, Amir Capua and Benjamin Assulin from the Hebrew University in Jerusalem, Israel, have demonstrated otherwise.

“We now recognize that the secondary aspect of light interacts with matter,” explains Capua.

Capua notes two reasons why the magnetic component of light’s involvement in the Faraday effect has been overlooked. Firstly, the magnetic forces present in materials like Faraday glass seem significantly weaker compared to their electrical counterparts. Secondly, when a substance such as Faraday glass is magnetized, the quantum spins of its constituents behave like miniature magnets and often fail to synchronize with the magnetic component of the light wave, implying minimal interaction.

However, Capua and Assulin realized that if the magnetic component of light is circularly polarized (spiral or corkscrew-shaped), it may engage more effectively with the magnetic spins within the glass. They reached this conclusion based on the observation that light’s magnetic component naturally comprises several corkscrew waves without needing any specialized manipulation.

The researchers’ calculations indicate that repeating Faraday’s experiment using a magnetic material called terbium gallium garnet (TGG) in place of glass could account for 17 percent of the Faraday effect noted when visible light travels through it. When infrared light traverses the TGG material, magnetic interactions could explain as much as 70 percent of the resulting Faraday effect.

Igor Rozhansky from the University of Manchester, UK, asserts that these new calculations are compelling and point towards feasible experimental inquiries. The previously overlooked magnetic component of the Faraday effect could unveil new methods for controlling spin within materials, according to Rozhansky. He suggested it remains an open question whether this effect might surpass the traditional Faraday effect in certain materials.

Future experiments may yield groundbreaking findings, spanning from fundamental physics to practical applications. Capua envisions the possibility of utilizing the interaction between the magnetic spin of select materials and the magnetic component of light to manipulate materials, potentially leading to innovative spin-based sensors and data storage systems.

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