Physicists Just Found a New Twist in the Faraday Effect Nearly 200 Years After Faraday Himself

A Familiar Experiment Suddenly Looks Different

Back in 1845, Michael Faraday did something surprisingly simple: he shined a beam of light through a piece of glass sitting inside a magnetic field. That’s it. No lasers, no superconducting coils, no fancy optics built by a team of grad students who haven’t slept in 48 hours. And yet, that modest little setup revealed that the polarization of light the direction its waves wiggle rotates when exposed to a magnetic field.

This became known as the Faraday effect, and for almost two centuries scientists felt pretty comfortable with the explanation: the electric part of light does all the heavy lifting. The magnetic part? More like the quiet sibling nobody invites to the group project.

But a team from the Hebrew University of Jerusalem has just forced everyone to rethink that old assumption. According to their new theoretical study, the magnetic field of light itself the half we usually ignore actually plays a direct role in the Faraday effect. And not a trivial one. It can significantly shift how materials twist the polarization of passing light.

As Dr. Amir Capua, one of the lead researchers, put it, “Light doesn’t just illuminate matter, it magnetically influences it.” His phrasing might sound dramatic, but the results back him up.

The Side of Light Everyone Forgot About

If you zoom in far enough, light is basically an electromagnetic wave. Two fields, electric and magnetic, doing a little synchronized dance. Physicists tend to pay attention to the electric field because it interacts with charged particles. That’s where most optical phenomena come from refraction, absorption, scattering, the things you learn in your first optics class.

The magnetic component, though? Historically considered too weak to do anything interesting in the Faraday effect. If the electric part was the main character, the magnetic part was the background extra who appears for half a second and doesn’t get a credit.

However, Capua and his colleague Benjamin Assouline argue that this view is incomplete. They suggest that light’s magnetic field even though it’s weaker can directly twist the spins of electrons in certain materials. Spins are quantum mechanical little arrows that give rise to magnetism in the first place. And if you can make those tiny arrows wobble or precess, you can change how the material interacts with light.

That’s exactly what the team’s modeling suggests.

Why Nobody Noticed This Before

You might wonder why, in almost 200 years, no one took a closer look at the magnetic side of the Faraday effect. It’s not because scientists were lazy. It’s because under most conditions, the magnetic force from light is weak compared to the electric force. And electron spins don’t always respond quickly enough to match the rapid oscillation of light waves.

It’s like trying to get a weather vane to spin perfectly in sync with a hummingbird’s wing flaps. The timing just isn’t compatible.

But and this is a big but when light is circularly polarized, something changes. Instead of vibrating back and forth like a violin string, the wave twists forward like a corkscrew. In that state, the magnetic field of the light becomes better aligned with the electron spins in a material. Suddenly, the magnetic component isn’t a background extra anymore. It’s a real actor.

To test this idea, the researchers used the Landau–Lifshitz–Gilbert equation, a well known mathematical tool used to describe how spins behave under magnetic fields. It’s the same equation used when designing magnetic storage devices or simulating spin based materials.

Plugging circularly polarized light into this model produces something new: a magnetic torque generated directly by the light’s own magnetic field.

Running the Numbers: A Material Tells the Story

Theory is great, but you still need real materials to test it. So Capua and Assouline turned to terbium gallium garnet (TGG) a crystal that’s a favorite in optical devices because it produces a strong Faraday effect even at room temperature. If any material were going to reveal hidden influences from light’s magnetic field, it would be TGG.

When they ran their model, the results were surprisingly bold:

In the visible light range, the magnetic component contributes roughly 17% of the total Faraday rotation.
In the infrared, that number jumps as high as 70%.

Seventy percent. That’s not a rounding error. That’s not noise. That’s basically discovering the quiet kid in class is writing half the group essay.

Assouline put it succinctly: “Light ‘talks’ to matter not only through its electric field, but also through its magnetic field.” And after seeing those numbers, it’s hard to argue against him.

Why This Matters More Than You’d Think

At first glance, you might think this is just a small correction to a dusty old optical effect. But the implications ripple out. Understanding how light couples magnetically to materials could influence:

optical communication technologies, where polarization control is king
spintronics, where electron spins carry information
magneto optical isolators used in lasers and quantum devices
even materials designed for future quantum computing platforms

More broadly, this discovery suggests we may have underappreciated the magnetic influence of light in a range of phenomena. If we’ve been ignoring half of light’s electromagnetic personality, then some “settled” theories may need revisiting.

Now, it’s worth noting that this is a theoretical prediction, not yet an experimental measurement. That doesn’t make it less exciting, but it does mean more work lies ahead. Other teams will try to detect the magnetic contribution directly something that could require extremely sensitive setups or materials engineered to amplify the effect.

Still, even with that caveat, the idea feels like one of those shifts that starts small but may eventually reshape how we teach electromagnetism.

A Nearly 200 Year Old Experiment Gets a Modern Update

Faraday couldn’t have imagined lasers, superconducting coils, or computer simulations running LLG equations. But in his own way, he opened the door to questions that scientists are still exploring.

What the Hebrew University team has shown is that the Faraday effect isn’t quite as simple as we thought. Light’s magnetic field isn’t just along for the ride it’s actively steering the interaction in ways we’re only now starting to understand.

And honestly, there’s something charming about that. Nearly two centuries later, an experiment first done with a lantern and a chunk of glass still has secrets left to reveal.

Open Your Mind !!!

Source: ZME

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