Magnetic structure of GdCo₂Ge₂

Resonant and nonresonant magnetic x-ray scattering studies of GdCo₂Ge₂ were performed to determine its magnetic structure at low temperature. This compound orders in an incommensurate antiferromagnetic (AF) structure characterized by a propagation wave vector τ=(0 0 τ_z). The value of τ_z is temperature dependent and approaches 0.930 reciprocal lattice units well below T_N=33.25 K. A peak corresponding to 3τ_z was also observed, indicating either a squaring up of the magnetic structure or the presence of a noncollinear amplitude modulated structure below T_N. Fitting the angular dependence of the magnetic scattering integrated intensities to the relevant resonant and nonresonant scattering cross sections revealed that the moment direction lies primarily in the tetragonal basal plane. Scattering measurements at the Co K- edge failed to detect any resonant signal, consistent with the absence of a magnetic moment on the Co sites.