Researchers from the University of Colorado Boulder have discovered why an ultra-thin magnet demagnetizes when hit by a laser. This phenomenon has puzzled scientists for a long period of time.
Their findings show that magnets regain their properties in a fraction of a second and was published in Nature Communications. "Zapped magnets actually behave like fluids. Their magnetic properties begin to form 'droplets,' similar to what happens when you shake up a jar of oil and water," according to Science Daily.
Lead researcher Ezio Iacocca with Mark Hoefer and other colleagues performed the study through numerical simulations, mathematical modeling, and experiments at the SLAC National Accelerator Laboratory at Stanford University.
"Researchers have been working hard to understand what happens when you blast a magnet," said Iacocca, lead author of the new study and a research associate in the Department of Applied Mathematics. "What we were interested in is what happens after you blast it. How does it recover?"
The team focused on a specific time interval -- the first 20 trillionths of a second after a short, high-energy laser hits a magnetic, metallic alloy.
Naturally, magnets are organized and their atomic have "spins" or orientations that go to the same direction. In layman's term, it could be the magnetic field of the Earth that always points north.
This only stops when a magnet is hit by a laser as there will be a disorder. The magnet spins in all different directions that cancels out the properties of the magnet.
"Researchers have addressed what happens 3 picoseconds after a laser pulse and then when the magnet is back at equilibrium after a microsecond," said Iacocca, also a guest researcher at the U.S. National Institute of Standards and Technology (NIST). "In between, there's a lot of unknown."
Iacocca and his team decided to find out what happens during that time of interval. They conducted experiments in California by pointing lasers to tiny pieces of gadolinium-iron-cobalt alloys. Results of the study were compared to that of computer simulations and mathematical predictions.
Things became fluid. Hoefer, an associate professor of applied math, iterated that the metals did not convert to liquid, rather, the magnetic spins acted like fluids. It is similar to waves in the ocean that change their orientation as they keep moving around.
"We used the mathematical equations that model these spins to show that they behaved like a superfluid at those short timescales," said Hoefer, a co-author of the new study.
The disoriented spins finally settle down after a while and forming small groups with the same spin. The droplets become bigger and bigger.
"In certain spots, the magnet starts to point up or down again," Hoefer said. "It's like a seed for these larger groupings."
The zapped magnet sometimes does not return to its original orientation as its spin could go from up to down.
This flipping behavior can be used for storage of information on a computer hard drive. If the researchers can control on how to change that flipping, there is a potential in building faster computers.
"That's why we want to understand exactly how this process happens," Iacocca said, "so we can maybe find a material that flips faster."
