Incommensurate Spin-Density Wave Order in Electron-Doped BaFe2As2 Superconductors

Neutron diffraction studies of Ba(Fe1-xCox-2)As-2 reveal that commensurate antiferromagnetic order gives way to incommensurate magnetic order for Co compositions between 0.056 < x < 0.06. The incommensurability has the form of a small transverse splitting (0, +/-epsilon, 0) from the commensurate antiferromagnetic propagation vector Q(AFM) = (1, 0, 1) (in orthorhombic notation) where epsilon approximate to 0.02 - 0.03 and is composition dependent. The results are consistent with the formation of a spin-density wave driven by Fermi surface nesting of electron and hole pockets and confirm the itinerant nature of magnetism in the iron arsenide superconductors.