A new kind of magnetic order has been observed in barium-cobalt iron arsenide high-temperature superconductors by researchers with expertise in growing large single crystals, conducting x-ray and neutron measurements, and calculating electronic structures. Traditional antiferromagnetic order observed, for example, in the copper oxide high-temperature superconductors is driven by strong electron-electron interactions that can result in insulating behavior. The new structure, called an antiferromagnetic spin-density wave, is also known to form in metals such as chromium when electron-electron interactions are weak. Thus, while all high-temperature superconductors seem to possess antiferromagnetic order of some sort, strong electron-electron interactions do not appear to be a universal requirement. This new discovery changes the constraints on the origin of high-temperature superconductivity.
D. K. Pratt, M. G. Kim, A. Kreyssig, Y. B. Lee, G. S. Tucker, A. Thaler, W. Tian, J. L. Zarestky, S. L. Bud'ko, P. C. Canfield, B. N. Harmon, A. I. Goldman and R. J. McQueeney "Incommensurate spin-density wave order in electron-doped BaFe2As2 superconductors" Physical Review Letters, 106, 257001 (2011).