Magnetic structure of $\mathrm{Gd}{\mathrm{Co}}_2{\mathrm{Ge}}_2$

Resonant and nonresonant magnetic x-ray scattering studies of 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 . The value of is temperature dependent and approaches 0.930 reciprocal lattice units well below . A peak corresponding to was also observed, indicating either a squaring up of the magnetic structure or the presence of a noncollinear amplitude modulated structure below . 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 - edge failed to detect any resonant signal, consistent with the absence of a magnetic moment on the Co sites.

Figure 1

SQUID susceptibility measurements with a field of $H=1\mathrm{kOe}$ applied parallel to the $c$ axis [001] or perpendicular to the $c$ axis [100]. The peak in the susceptibility is at approximately 33 K.

Figure 2

Longitudinal scans across the (0 0 $L$) reflections at 6 and 40 K taken at the $\mathrm{Gd}{L}_{\mathrm{III}}$ edge. The 6 K data are offset relative to the 40 K data.

Figure 3

Temperature dependence of the wave vector in reciprocal space measured relative to the (008) peak position using the (0 0 $8\text{−}{\tau }_z$) and (0 0 $8+{\tau }_z$) satellites measured at the $\mathrm{Gd}{L}_{\mathrm{III}}$ edge.

Figure 4

Energy scans of (a) the scattered intensity at the (0 0 8) peak position and (b) the dipole resonance at the (0 0 $8\text{−}{\tau }_z$) satellite peak position. The dashed line marks the position of the $\mathrm{Gd}{L}_{\mathrm{III}}$ absorption edge.

Figure 5

Order parameter measurement used to determine $T_N$ measured at the $\mathrm{Gd}{L}_{\mathrm{III}}$ edge. The inset shows the plot of order parameter versus reduced temperature $(1-T∕T_N)$. The solid line is a fit using a $I=A{(1-T∕T_N)}^{2\beta }$ for temperatures close to $T_N$.

Figure 6

Angular dependence of the integrated intensity measured at the $\mathrm{Gd}{L}_{\mathrm{III}}$ edge at $T=6\mathrm{K}$. The solid line represents the theoretical prediction for a moment direction aligned perpendicular to the $c$ axis. The dashed line represents a moment direction aligned along the $c$ axis.

Figure 7

Nonresonant $Q$ dependence of the integrated intensity measured using an incident beam energy of 7 keV at $T=6\mathrm{K}$. The solid line represents the scattering cross section for the magnetic moment aligned perpendicular to the $c$ axis. The dashed line represents the scattering cross section for the magnetic moment aligned parallel to $c$.