Magnetic structure of ${\mathrm{GdAgSb}}_2$ determined by x-ray resonant exchange scattering

X-ray resonant exchange-scattering experiments were performed on a single crystal of ${\mathrm{GdAgSb}}_2$ to determine the magnetic structure. Long-range antiferromagnetic ordering, characterized by a wave vector of $\overrightarrow{\tau }=\left(\frac{1}{2}00\right),$ develops below the Néel temperature ${(T}_N=13\mathrm{}\hspace{0.5em}\mathrm{K}),$ consistent with the dc susceptibility measurements. For the scattering geometry employed in these measurements, the resonant enhancement at the $\left(\frac{1}{2}08\right)$ magnetic peak arises from electric quadrupole transitions only while the resonant enhancement at the $\left(0\mathrm{}-\frac{1}{2}8\right)$ magnetic peak arises from electric dipole transitions. Q-dependent integrated intensity measurements were carried out, along with polarization analysis of the scattered beam, and demonstrated that the moments lie in the tetragonal basal plane and are perpendicular to the magnetic wave vector.