Iron-based superconductor

Iron-based superconductors (sometimes misleadingly called Iron superconductors) are (in 2008) in the first stages of experimentation and implementation. Previously most high temperature superconductors were cuprates and were therefore based on layers of copper sandwiched between other (typically non-metal) substances. This new type of superconductors is based instead on layers of iron and arsenic and seems to show promise as the next generation of high temperature superconductors Scientific American June 2008] . They belong to the group of oxypnictides. Some of the compounds are known since 1995 cite journal
title = The rate earth transition metal phosphide oxides LnFePO, LnRuPO and LnCoPO with ZrCuSiAs type structure
author = Barbara I. Zimmer, Wolfgang Jeitschko, Jörg H. Albering, Robert Glaum and Manfred Reehuis
journal = Journal of Alloys and Compounds
volume = 229
issue = 2
pages = 238-242
year = 1995
url =
doi = 10.1016/0925-8388(95)01672-4 ] and their semiconductive properties are known and patented since 2006.cite journal
title = Iron-Based Layered Superconductor: LaOFeP
author = Yoichi Kamihara, Hidenori Hiramatsu, Masahiro Hirano, Ryuto Kawamura, Hiroshi Yanagi, Toshio Kamiya, and Hideo Hosono
journal = J. Am. Chem. Soc.
volume = 128
issue = 31
pages = 10012 -10013
year = 2006
url =
doi = 10.1021/ja063355c S0002-7863(06)03355-5 ] [http://www.freepatentsonline.com/EP1868215.html MAGNETIC SEMICONDUCTOR MATERIAL ]

The crystalline material, known chemically as LaOFeAs, stacks iron and arsenic layers, where the electrons flow, between planes of lanthanum and oxygen. Replacing up to 11 percent of the oxygen with fluorine improved the compound — it became superconductive at 26 kelvins, the team reports in the March 19 2008 Journal of the American Chemical Society. Subsequent research from other groups suggests that replacing the lanthanum in LaOFeAs with other rare earth elements such as cerium, samarium, neodymium and praseodymium leads to superconductors that work at 52 kelvins.

Methods of operation

Modern conventional superconductors work at temperatures between absolute zero and 100 kelvin. Certain cuprates became superconductive at temperatures exceeding 163 kelvins. Ordinarily in cuprate superconductors the electrons are paired due to spin fluctuations that occur around the copper ions. However in iron based superconductors orbital fluctuations are far more essential.

On the other hand, the spin fluctuations that could glue together cuprate electrons might not be enough for those in the iron-based materials. Instead orbital fluctuations — or variations in the location of electrons around atoms — might also prove crucial, Haule speculates. In essence, the iron-based materials give more freedom to electrons than cuprates do when it comes to how electrons circle around atoms.

Orbital fluctuations might play important roles in other unconventional superconductors as well, such as ones based on uranium or cobalt, which operate closer to absolute zero, Haule conjectures. Because the iron-based superconductors work at higher temperatures, such fluctuations may be easier to research. [ [http://www.sciam.com/article.cfm?id=iron-exposed-as-high-temp-superconductor Iron Exposed as High-Temperature Superconductor: Scientific American ] ]

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