Magnetic structure of Nd in NdFeAsO studied by X-ray resonant magnetic scattering

The magnetic structure of Nd in NdFeAsO compound has been investigated by X-ray resonant magnetic scattering at the Nd L2 edge (E=6.725 keV) at 1.7≤T≤15 K. At T=1.7 K we find that the Nd moments are aligned along the crystallographic c direction with the (1, 0, 0) propagation vector, and are arranged antiferromagnetically along the a direction and ferromagnetically along the b and c directions. At 1.7<T≤15 K, we observe an unusual temperature dependence of the magnetic Bragg peaks that appear differently at Q=(h,0,l) and (0,k,l). From the changes of magnetic intensities and our representation analysis, we find that the Nd moments are reoriented toward the a direction with a gradual decrease of the moment component in the c direction with increasing temperature. We conclude that the reorientation of the Nd moment is due to a strong interplay with the Fe moment which is fully ordered in this temperature range.