彩民宝典

For years, researchers have pursued a strange phenomenon: When you hit an ultra-thin magnet with a laser, it abruptly听de-magnetizes. Imagine the magnet on your refrigerator suddenly falling off.

Now, scientists at 彩民宝典听are digging听into how magnets recover from that change, regaining their properties in a fraction of a second.听

According to a study , zapped magnets actually behave like fluids. Their magnetic properties begin to form 鈥渄roplets,鈥� similar to what happens when you shake up a jar of oil and water.

To find that out, 彩民宝典鈥檚 Ezio Iacocca, Mark Hoefer and their colleagues drew on mathematical modeling, numerical simulations and experiments conducted at Stanford University鈥檚 .

鈥淩esearchers have been working hard to understand what happens when you blast a magnet,鈥� said Iacocca, lead author of the new study and a research associate in the Department of Applied Mathematics. 鈥淲hat we were interested in is what happens after you blast it. How does it recover?鈥�

In particular, the group zeroed in on a short but critical time in the life of a magnet鈥攖he 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 鈥渟pins,鈥� that tend to point in the same direction, either up or down鈥攖hink of Earth鈥檚 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 metal鈥檚 magnetic properties.听

鈥淩esearchers have addressed what happens 3 picoseconds after a laser pulse and then when the magnet is back at equilibrium after a microsecond,鈥� said Iacocca, also a guest researcher at the (NIST). 鈥淚n between, there鈥檚 a lot of unknown.鈥�

The unknown

It鈥檚 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.听

And, the group discovered, things got fluid. Hoefer, an associate professor of applied math, is quick to point out that the metals themselves didn鈥檛 turn into liquid. But the spins within those magnets behaved like fluids, moving around and changing their orientation like waves crashing in an ocean.

听鈥淲e used the mathematical equations that model these spins to show that they behaved like a superfluid at those short timescales,鈥� said Hoefer, a co-author of the new study. 听

Wait a little while and those roving spins start to settle down, he added, forming small clusters with the same orientation鈥攊n essence, 鈥渄roplets鈥� 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.听

鈥淚n certain spots, the magnet starts to point up or down again,鈥� Hoefer said. 鈥淚t鈥檚 like a seed for these larger groupings.鈥�

Hoefer added that a zapped magnet doesn鈥檛 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.听

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.听 Iacocca said that if听researchers can figure out ways to do that flipping more efficiently,听they might be able to build faster computers.

鈥淭hat鈥檚 why we want to understand exactly how this process happens,鈥� Iacocca said, 鈥渟o we can maybe find a material that flips faster.鈥�

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, Ca鈥� Foscari University of Venice, Temple University, European X-Ray Free-Electron Laser Facility, Nihon University, Radboud University, University of Li猫ge, Sheffield Hallam University and Uppsala University.