Doping evolution of antiferromagnetic order and structural distortion inLaFeAsO1−xFx

Abstract

We use neutron scattering to study the structural distortion and antiferromagnetic ͑AFM͒ order in LaFeAsO 1−x F x as the system is doped with fluorine ͑F͒ to induce superconductivity. In the undoped state, LaFeAsO exhibits a structural distortion, changing the symmetry from tetragonal ͑space group P4 / nmm͒ to orthorhombic ͑space group Cmma͒ at 155 K, and then followed by an AFM order at 137 K. Doping the system with F gradually decreases the structural distortion temperature, but suppresses the long range AFM order before the emergence of superconductivity. Therefore, while superconductivity in these Fe oxypnictides can survive in either the tetragonal or the orthorhombic crystal structure, it competes directly with static AFM order.

Phase diagram of thePrFeAsO1−xFxsuperconductor

“…Within the phase diagram of CeFeAsO 1−x F x , J. Zhao et al 7 argue for a suppression of the antiferromagnetism (AFM) with doping such that the magnetic order vanishes in close proximity to the superconductivity. This has been confirmed in other LnFeAsO 1−x F x systems 2, 7,10,14,15,16,17,18,19 . Yet, in SmFeAsO 1−x F x there are reports of coexistence of static AFM order with superconductivity 20,21 .…”

“…Among the iron-pnictides, to-date, the electron-doped (O 1−x F x ) iron-arsenides LnFeAsO 1−x F x have the highest T C 's reported. Until now, there have been reports on the phase diagrams of LnFeAsO 1−x F x , Ln=La 1, 10,14,15,16,17 , Ce 2,7 , Nd 18 , and Sm 19,20,21 . Within the phase diagram of CeFeAsO 1−x F x , J. Zhao et al 7 argue for a suppression of the antiferromagnetism (AFM) with doping such that the magnetic order vanishes in close proximity to the superconductivity.…”

Antiferromagnetic order and spin dynamics in iron-based superconductors

“…3(d). Another equivalent Brillouin zone near Γ is marked by the magenta dashed line, while the first Brillouin zone of the chemical unit Huang et al, 2008b;McGuire et al, 2008;Qureshi et al, 2010).…”

Relationship between Superconductivity and Antiferromagnetism in LaFe(As1−xPx)O Revealed by 31P-NMR

“…In LaFe(As 1−x P x )O, the AFM order is continuously suppressed with P substitution, whereas the AFM order suddenly disappears with the first-order-like transition against F content in LaFeAs(O 1−x F x ). [32][33][34] These experimental results suggest that there are at least two pairing mechanisms in iron-based superconductors.…”