When zapped with a laser, magnets behave like fluids

By Brooks Hays
Researchers have discovered how magnetic particles reorganize their spins in the wake of the disruption caused by a laser blast. Photo by Benjamin Crowell/Wikimedia Commons
Researchers have discovered how magnetic particles reorganize their spins in the wake of the disruption caused by a laser blast. Photo by Benjamin Crowell/Wikimedia Commons

April 18 (UPI) -- Scientists have managed to figure out how a magnet manages to recover after being demagnetized by a brief laser blast. The discovery suggests lasers make magnets behave like fluids.

When an ultra thin magnet is hit with a laser, it suddenly becomes demagnetized.


Materials with magnetic properties feature subatomic building blocks all spinning in the same direction. There is order to the organization of the magnet's particles -- a laser blast disrupts this order.

Scientists have previously detailed the atomic chaos that ensues in the wake of the laser strike. And researchers know what a magnet looks like once it's reorganized. The recovery process, which lasts just a fraction of a second, has, until now, remained poorly understood.

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"Researchers have addressed what happens 3 picoseconds after a laser pulse and then when the magnet is back at equilibrium after a microsecond," mathematician Ezio Iacocca, researcher at the University of Colorado, Boulder, said in a news release. "In between, there's a lot of unknown."

In the lab, researchers blasted gadolinium-iron-cobalt alloys with lasers. They compared the results of their experiments with computer simulations designed to predict the behavior of laser-blasted atoms.


The mathematical formulas describing the atoms showed the magnetized particles behave like a fluid in the wake of a laser blast. The material, or magnet, itself doesn't become fluid-like, but the atomic spins behave like a fluid. The spin directions of the magnet's atomic units slosh around like ocean waves.

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"We used the mathematical equations that model these spins to show that they behaved like a superfluid at those short timescales," said Mark Hoefer, researcher at CU Boulder.

Researchers shared the results of their analysis this week in the journal Nature Communications.

If the surface of a calm pond on a windless day represents a magnet and its atomic spins, all perfectly synchronized, a laser blast is like a big rock tossed into the middle. Slowly but surely, the violent splash that results turns into gentle ripples, and soon enough, the surface of the pond is glassy smooth again.

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Hoefer likens the phenomena to a jar of oil and water that gets shaken. Once the shaking stop, bits of oil start to coalesce, forming larger and larger clumps until the oil and water are separated once more.

"In certain spots, the magnet starts to point up or down again," Hoefer said. "It's like a seed for these larger groupings."


Sometimes magnets reorganize their spins in the opposite direction after a disruption. Computer engineers take advantage of spin flips when they store information on computer hard drives. If scientist could find a way to engineer magnets capable of flipping their spins faster, they might be able to boost computer processing speeds.

"That's why we want to understand exactly how this process happens, so we can maybe find a material that flips faster," Iacocca said.

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