A variable temperature study of the crystal and magnetic structures of   the giant magnetoresistant materials LnMnAsO (Ln = La, Nd)
  A variable temperature neutron and synchrotron diffraction study have been performed on the giant magnetoresistant oxypnictides LnMnAsO (Ln = La, Nd). The low temperature magnetic structures have been studied and results show a spin reorientation of the Mn2+ spins below TN (Nd) for NdMnAsO. The Mn2+ spins rotate from alignment along c to alignment into the basal plane and the Mn2+ and Nd3+ moments refine to 3.54(4) \mu B and 1.93(4) \mu B respectively at 2 K. In contrast there is no change in magnetic structure with temperature for LaMnAsO. There is no evidence of a structural transition down to 2 K, however discontinuities in the cell volume, Ln-O and Mn-As bond lengths are detected at \sim 150 K for both materials. This temperature coincides with the electronic transition previously reported and suggests a coupling between electronic and lattice degrees of freedom. 
N. Emery, E. J. Wildman, J. M. S. Skakle, R. I. Smith, A. N. Fitch and   A. C. Mclaughlin
cond-mat.str-el cond-mat.mtrl-sci cond-mat.other