Einstein–de Haas effect offers new insight into a puzzling magnetic phenomenon

phys.org | 1/15/2019 | Staff
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More than 100 years ago, Albert Einstein and Wander Johannes de Haas discovered that when they used a magnetic field to flip the magnetic state of an iron bar dangling from a thread, the bar began to rotate.

Now experiments at the Department of Energy's SLAC National Accelerator Laboratory have seen for the first time what happens when magnetic materials are demagnetized at ultrafast speeds of millionths of a billionth of a second: The atoms on the surface of the material move, much like the iron bar did. The work, done at SLAC's Linac Coherent Light Source (LCLS) X-ray laser, was published in Nature earlier this month.

Dornes - Scientist - ETH - Zurich - Switzerland

Christian Dornes, a scientist at ETH Zurich in Switzerland and one of the lead authors of the report, says this experiment shows how ultrafast demagnetization goes hand in hand with what's known as the Einstein-de Haas effect, solving a longstanding mystery in the field.

"I learned about these phenomena in my classes, but to actually see firsthand that the transfer of angular momentum actually makes something move mechanically is really cool," Dornes says. "Being able to work on the atomic scale like this and see relatively directly what happens would have been a total dream for the great physicists of a hundred years ago."

Scale - Material - Magnetism - Electrons - Magnets

At the atomic scale, a material owes its magnetism to its electrons. In strong magnets, the magnetism comes from a quantum property of electrons called spin. Although electron spin does not involve a literal rotation of the electron, the electron acts in some ways like a tiny spinning ball of charge. When most of the spins point in the same direction, like a sea of ice skaters pirouetting in unison, the material becomes magnetic.

When the magnetization of the material is reversed with an external magnetic field, the synchronized dance of the skaters turns...
(Excerpt) Read more at: phys.org
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