Abstract
The recent discovery of superconductivity in , which crystallizes in the (122) structure as compared with the LnFeAsO (Ln is lanthanide) systems that possess the ZrCuSiAs (1111) structure, demonstrates the exciting potential of the FeAs-based materials for high- superconductivity. Here we report neutron diffraction studies that show a tetragonal-to-orthorhombic distortion associated with the onset of antiferromagnetic order in , with a saturation moment per Fe that is orientated along the longer axis of the planes. The simultaneous first-order structural and magnetic transition is in contrast with the separated transitions previously reported in the 1111-type materials. The orientational relation between magnetic alignment and lattice distortion supports a multiorbital nature for the magnetic order.
- Received 14 July 2008
DOI:https://doi.org/10.1103/PhysRevLett.101.257003
©2008 American Physical Society