The shape and variation of magnetization density in Fe-As based superconductors have been determined for the first time. Understanding details of the magnetism may provide insight into the factors that control the superconducting transition temperature. Measurement of the magnetic density can help determine how antiferromagnetic fluctuations contribute to or hinder the high superconducting transition temperatures observed. The spatial distribution of the magnetization density in Strontium Iron Arsenic (SrFe2As2) has been measured (using neutron scattering) and has been calculated (using density functional theory). Experiment and theory are in excellent agreement for the shape of the magnetization density, which is dominated by Fe, with a radial distribution very similar to that found in elemental Fe metal. However, the magnitude of the experimental iron moment in SrFe2As2 at low temperature is only about half the size of that in elemental Fe. As known from previous studies, the size of the calculated magnetic moment is quite sensitive to slight changes in the As atom position, but the shape of the magnetization density is not. While all five iron 3d orbitals contribute substantially to the magnetic moment, their contributions vary by about a factor of two, creating anisotropy of the magnetization density.
- Y. Lee, David Vaknin, Haifeng Li, Wei Tian, Jerel L. Zarestky, N. Ni, S. L. Bud'ko, P. C. Canfield, R. J. McQueeney, and B. N. Harmon "Magnetic form factor of iron in SrFe2As2" Phys. Rev. B. 81, 060406 (2010)