Posted in | Laser

Study Shows Zapped Magnets Behave Like Fluids When Hit by a Short, High-Energy Laser

Scientists have long been pursuing an unusual phenomenon—when an ultra-thin magnet is hit with a laser, it will de-magnetize quickly. This can be compared to a magnet fixed on a refrigerator which abruptly falls off.

A computer simulation of magnetic "droplets" forming juxtaposed with a photo of oil in water. (Image credit: Ezio Iacocca; Pixabay)

Now, a research team at the University of Colorado Boulder (CU Boulder) is exploring how magnets are able to recover from that change and regain their characteristics, all in just a fraction of a second.

According to a research recently featured in Nature Communications, zapped magnets essentially act like fluids. The magnetic properties of these magnets start to create “droplets,” akin to what occurs when a jar of water and oil is shaken up.

In order to find out that phenomenon, Mark Hoefer, Ezio Iacocca, and their colleagues from CU Boulder drew on numerical simulations, mathematical modeling, and experiments performed at the SLAC National Accelerator Laboratory of Stanford University.

Researchers have been working hard to understand what happens when you blast a magnet. What we were interested in is what happens after you blast it. How does it recover?

Ezio Iacocca, Study Lead Author and Research Associate, Department of Applied Mathematics, University of Colorado, Boulder

The researchers specifically focused on a short yet crucial time in a magnet’s life—that is, the initial 20 trillionths of a second after a short, high-energy laser hits a magnetic, metallic alloy.

By nature, magnets are well organized, explained Iacocca. The atomic building blocks of magnets have “spins” or orientations that have a tendency to point in the same direction, either down or up—envision the magnetic field of Earth, invariably pointing north. Except, that is, when they are hit with a laser. Disorder will occur when a magnet is hit with a sufficiently short laser pulse, informed Iacocca. Within a magnet, the spins will not point up or down anymore but will do so in all different directions, nullifying the magnetic properties of the metal.

Researchers have addressed what happens 3 picoseconds after a laser pulse and then when the magnet is back at equilibrium after a microsecond. In between, there’s a lot of unknown.

Ezio Iacocca, Study Lead Author and Research Associate, Department of Applied Mathematics, University of Colorado, Boulder

Iacocca is also a guest researcher at the U.S. National Institute of Standards and Technology (NIST).

The unknown

Iacocca and his coworkers wanted to fill in that exact missing window of time. In order to accomplish that, the researchers conducted a set of experiments in California, using lasers to blast small pieces of gadolinium-iron-cobalt alloys. They subsequently compared the outcomes to computer simulations and mathematical predictions.

And things got fluid, discovered the research team. Hoefer, an associate professor of applied math quickly pointed out that the metals themselves did not convert into a liquid, but rather the spins inside those magnets acted like fluids, shifting around and altering their orientation similar to how waves crash in an ocean.

We used the mathematical equations that model these spins to show that they behaved like a superfluid at those short timescales.

Mark Hoefer, Study Co-Author and Associate Professor, Department of Applied Mathematics, University of Colorado, Boulder

Hoefer added that if one waits a little while, those roving spins will begin to settle down, creating tiny clusters with the same direction—essentially, “droplets” wherein the spins are all pointed in an upward or downward direction. If one waits a little longer, those droplets would become progressively bigger, estimated the research team, and thus the comparison to water and oil isolating out in a jar.

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

A zapped magnet does not invariably revert to the way it once was, added Hoefer. In certain cases, a magnet can turn following a laser pulse, changing from up to down. That flipping behavior is already being exploited by engineers to store data on the hard drive of a computer in the form of bits of zeros and ones. Figuring out ways to do that flipping process in a more efficient manner may allow scientists to develop faster computers, stated Iacocca.

That’s why we want to understand exactly how this process happens. so we can maybe find a material that flips faster.

Ezio Iacocca, Study Lead Author and a Research Associate, Department of Applied Mathematics, University of Colorado, Boulder

The U.S. Department of Energy, Basic Energy Sciences partly supported the study.

The study co-authors also include researchers SLAC National Accelerator Laboratory, Chalmers University of Technology, University of York, Tongji University, Ca’ Foscari University of Venice, Stockholm University, Temple University, Nihon University, Radboud University, European X-Ray Free-Electron Laser Facility, University of Liège, Uppsala University, and Sheffield Hallam University.

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