Irradiated Magnets Behave Like Fluids to Regain Magnetic Properties

When an ultrathin magnet is hit with a laser, it demagnetizes and then recovers. Scientists at the University of Colorado at Boulder (CU Boulder) are investigating how magnets recover from demagnetization, regaining magnetic properties in a fraction of a second. The research could provide new insights into how to achieve desired metastable states.

The CU Boulder team zeroed in on the first 20 trillionths of a second after a magnetic, metallic alloy is hit by a short, high-energy laser. They ran a series of experiments, blasting tiny pieces of gadolinium-iron-cobalt alloys with lasers. The researchers found that when an ultrashort laser pulse was directed at the magnetic alloy, the spins within the magnet, normally well ordered, no longer pointed either up or down, but in all different directions, negating all magnetic properties of the alloy.

A computer simulation of the forming of magnetic 'droplets,' juxtaposed with a photo of oil in water. Courtesy of Ezio Iacocca/Pixabay.

They compared the experimental results to mathematical modeling and numerical simulations, and discovered that the spins within the magnets behaved like fluids, moving around and changing their orientation.

“We used the mathematical equations that model these spins to show that they behaved like a superfluid at those short timescales,” professor Mark Hoefer said. After a short period, the spins started to settle down, forming small clusters that had the same orientation — similar to forming “droplets” — in which the spins all pointed up or down. The researchers calculated that the spin clusters would grow bigger over time.

“In certain spots, the magnet starts to point up or down again,” Hoefer said. “It’s like a seed for these larger groupings.” The magnet did not always go back to the way it was before the laser pulse, the researchers said. In some cases, a magnet would flip after a laser pulse, switching from up to down.

Engineers already take advantage of this flipping behavior to store information on hard drives in the form of bits of ones and zeros. Researcher Ezio Iacocca said that if the team can figure out how to manage this flipping behavior more efficiently, their insights could help engineers build faster computers. “That’s why we want to understand exactly how this process happens — so we can maybe find a material that flips faster.”

The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-09577-0).