Gas Exhibits Magnetic Behavior

After more than 10 years of arduous debate in the international scientific community as to whether gas and liquids can exhibit magnetic properties, and become ferromagnets, an international collaboration has brought the final arguments to the table. The scientists involved in the new research managed to observed magnetic behavior in an atomic gas for the first time, essentially settling this issue. The lithium-atom gas was trapped in the focus of an infrared laser beam at the time of the study.

“Magnets are all around us – holding postcards on the refrigerator, pointing to magnetic north on a compass, and in speakers and headphones – yet some mysteries remain. We have perhaps found the simplest situation in which permanent magnetism can exist,” explains University of Toronto professor of physics Joseph H. Thywissen. He is also a visiting member at the Massachusetts Institute of Technology-based team that was in charge of the new research. The atomic gas was less than a millionth of a degree above absolute zero, which is at -273 degrees Celsius (roughly 150 nK).

The ferromagnetic behavior became obvious to the investigators when they gradually increased the repulsive forces between the atoms in the mix. Other traits modified as well. At first, the gas increased in volume considerably, and then shrunk considerably. When the laser containment was discontinued, the gas also expanded incredibly fast, the team reports. Details appear in the September 18 issue of the top journal Science, in a paper entitled “Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms.”

“Magnetism only occurs in a strongly interacting regime, where calculations – even using today's fastest computers – are difficult. Since naturally occurring gases do not have strong enough interactions to address the question, we turned to ultra-cold gases for answers,” says Thywissen. A common material becomes ferromagnetic when, even in the absence of strong magnetic fields, they begin exhibiting magnetic behavior. Funding for the new paper was obtained from the National Science and Engineering Research Council (NSERC) and the Canadian Institute for Advanced Research (CifAR).

“The evidence is pretty strong, but it is not yet a slam dunk. We were not able to observe regions where the atoms all point in the same direction. They started to form molecules and may not have had enough time to align themselves,” explains the co-principal investigator of the study, MIT physics professor David E. Pritchard. “We assumed that ferromagnetism did exist for a gas, and then asked what its properties would be. Surprisingly, we found there were simple energetic signatures of ferromagnetism – that were eventually observed at MIT,” says graduate student Lindsay LeBlanc.