title: Crystal structure and antiferromagnetic order in NdFeAsO1-xFx (x=0.0 and 0.2) superconducting compounds from neutron diffraction measurements.
abstract: The transition temperature T{C} approximately 26 K of the recently discovered superconductor LaFeAsO1-xFx is extremely sensitive to the lanthanide ion, reaching 55 K for the Sm containing oxypnictides. Therefore, it is important to determine how the moment on the lanthanide affects the overall magnetism in these systems. Here we report a neutron diffraction study of the Nd oxypnictides. Long-ranged antiferromagnetic order is apparent in NdFeAsO below 1.96 K. Rietveld refinement shows that both Fe and Nd magnetic ordering are required to describe the observed data with the staggered moment 1.55(4)micro{B}/Nd and 0.9(1)micro{B}/Fe at 0.3 K. The other structural properties such as the tetragonal-orthorhombic distortion are found to be very similar to those in LaFeAsO. Neither the magnetic ordering nor the structural distortion occur in the superconducting sample NdFeAsO0.80F0.20 at any temperatures down to 1.5 K.
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Qiu
authors.forename: Wei
authors.initials: W
authors.lastname: Bao
authors.forename: Q
authors.initials: Q
authors.lastname: Huang
authors.forename: T
authors.initials: T
authors.lastname: Yildirim
authors.forename: J M
authors.initials: JM
authors.lastname: Simmons
authors.forename: M A
authors.initials: MA
authors.lastname: Green
authors.forename: J W
authors.initials: JW
authors.lastname: Lynn
authors.forename: Y C
authors.initials: YC
authors.lastname: Gasparovic
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: T
authors.initials: T
authors.lastname: Wu
authors.forename: G
authors.initials: G
authors.lastname: Wu
authors.forename: X H
authors.initials: XH
authors.lastname: Chen