Magnetism Governs Properties of Iron-Based Superconductors
(萌妹社区Org.com) -- Though a year has passed since the discovery of a new family of high-temperature superconductors, a viable explanation for the iron-based materials鈥� unusual talent remains elusive. But a team of scientists working at the National Institute of Standards and Technology (NIST) may be close to the answer.
The team has found strong evidence that magnetism is a pivotal factor governing the physical properties of iron pnictides, a group of materials that conduct electricity without resistance at temperatures of up to 56 kelvin (-217 degrees celsius). Iron pnictides are composed of regularly spaced layers of iron sandwiched between other substances. And although -217 might sound pretty cold, they are the first class of materials found to superconduct at that high a temperature since the discovery of copper-based superconductors more than two decades ago.
The team鈥檚 evidence shows that without taking magnetism into account, theoretical calculations of iron pnictides鈥� inner structure do not line up with actual lab measurements. Factor in magnetism, though, and these discrepancies vanish鈥攁 decisive difference that, according to theorist Taner Yildirim, could imply that magnetism is also key to iron pnictide superconductivity.
鈥淲ithout considering magnetism, for example, the calculated distance between iron layers鈥攁 distance that has been thoroughly measured鈥攃omes out to be wrong,鈥� says Yildirim, of NIST鈥檚 Center for Neutron Research. 鈥淗owever, provided that we consider magnetic spin in our calculations, we can explain almost all of the iron pnictides鈥� structural and dynamic properties.鈥�
Yildirim gave an invited talk at the March meeting of the American 萌妹社区ical Society, where he presented theoretical evidence demonstrating how magnetism controls basic aspects of iron pnictides as the position of the atoms, the materials鈥� phase transition i.e. the sudden changes in the structure with temperature, and鈥攑robably, Yildirim says鈥攖heir superconducting properties.
鈥淒etermining the mechanism of superconductivity in iron pnictide systems is very important in solving the long-standing mystery of the high temperature superconductor phenomena in general,鈥� Yildirim said. 鈥淥nce we have such an understanding of this strange phenomenon, we can then make predictions and design new materials with even higher superconductivity temperatures.鈥�
More information: T. Yildrim. Competing magnetic interactions, structural phase transition, and the unprecedented giant coupling of Fe-spin state and the As-As interactions in iron-pnictide. Presented at the March Meeting of the American 萌妹社区ical Society, March 17, 2009. An abstract is available at .
Provided by National Institute of Standards and Technology ( : )
