For years, researchers have pursued a strange phenomenon: When you hit an ultra-thin magnet with a laser, it abruptlyÌęde-magnetizes. Imagine the magnet on your refrigerator suddenly falling off.
Now, scientists at CU BoulderÌęare diggingÌęinto how magnets recover from that change, regaining their properties in a fraction of a second.Ìę
According to a study , zapped magnets actually behave like fluids. Their magnetic properties begin to form âdroplets,â similar to what happens when you shake up a jar of oil and water.
To find that out, CU Boulderâs Ezio Iacocca, Mark Hoefer and their colleagues drew on mathematical modeling, numerical simulations and experiments conducted at Stanford Universityâs .
âResearchers have been working hard to understand what happens when you blast a magnet,â said Iacocca, lead author of the new study and a research associate in the Department of Applied Mathematics. âWhat we were interested in is what happens after you blast it. How does it recover?â
In particular, the group zeroed in on a short but critical time in the life of a magnetâthe first 20 trillionths of a second after a magnetic, metallic alloy gets hit by a short, high-energy laser.
Iacocca explained that magnets are, by their nature, pretty organized. Their atomic building blocks have orientations, or âspins,â that tend to point in the same direction, either up or downâthink of Earthâs magnetic field, which always points north.
Except, that is, when you blast them with a laser. Hit a magnet with a short enough laser pulse, Iacocca said, and disorder will ensue. The spins within a magnet will no longer point just up or down, but in all different directions, canceling out the metalâs magnetic properties.Ìę
âResearchers have addressed what happens 3 picoseconds after a laser pulse and then when the magnet is back at equilibrium after a microsecond,â said Iacocca, also a guest researcher at the (NIST). âIn between, thereâs a lot of unknown.â
The unknown
Itâs that missing window of time that Iacocca and his colleagues wanted to fill in. To do that, the research team ran a series of experiments in California, blasting tiny pieces of gadolinium-iron-cobalt alloys with lasers. Then, they compared the results to mathematical predictions and computer simulations.Ìę
And, the group discovered, things got fluid. Hoefer, an associate professor of applied math, is quick to point out that the metals themselves didnât turn into liquid. But the spins within those magnets behaved like fluids, moving around and changing their orientation like waves crashing in an ocean.
ÌęâWe used the mathematical equations that model these spins to show that they behaved like a superfluid at those short timescales,â said Hoefer, a co-author of the new study. Ìę
Wait a little while and those roving spins start to settle down, he added, forming small clusters with the same orientationâin essence, âdropletsâ in which the spins all pointed up or down. Wait a bit longer, and the researchers calculated that those droplets would grow bigger and bigger, hence the comparison to oil and water separating out in a jar.Ìę
âIn certain spots, the magnet starts to point up or down again,â Hoefer said. âItâs like a seed for these larger groupings.â
Hoefer added that a zapped magnet doesnât always go back to the way it once was. In some cases, a magnet can flip after a laser pulse, switching from up to down.Ìę
Engineers already take advantage of that flipping behavior to store information on a computer hard drive in the form of bits of ones and zeros.Ìę Iacocca said that ifÌęresearchers can figure out ways to do that flipping more efficiently,Ìęthey might be able to build faster computers.
âThatâs why we want to understand exactly how this process happens,â Iacocca said, âso we can maybe find a material that flips faster.â
The research was partly supported by the U.S. Department of Energy, Basic Energy Sciences.
Co-authors on the study also included researchers at Chalmers University of Technology, SLAC National Accelerator Laboratory, Tongji University, University of York, Stockholm University, Caâ Foscari University of Venice, Temple University, European X-Ray Free-Electron Laser Facility, Nihon University, Radboud University, University of LiĂšge, Sheffield Hallam University and Uppsala University.