Antiferromagnetic order and lattice response in DyCuAs$_2$

Abstract: We report high-resolution synchrotron X-ray diffraction and X-ray resonant magnetic scattering (XRMS) studies of the low-temperature crystal and magnetic structures of DyCuAs$<em>2$, a member of the \RE{}CuAs$_2$ family exhibiting a resistivity minimum above the antiferromagnetic transition temperature. Synchrotron diffraction measurements reveal that DyCuAs$_2$ preserves tetragonal symmetry down to low temperature within the experimental resolution, although pronounced anomalies in both lattice parameters $a$ and $c$ are observed near the antiferromagnetic transition temperature, $T</em>{\mathrm N}\approx7$~K, indicating strong magnetoelastic coupling. XRMS measurements at the Dy $L_3$ edge establish commensurate antiferromagnetic ordering below $T_{\mathrm N}$ with AFM Bragg peaks at \qq{} = (0, 0, 0.5). Representation analysis and calculations of the AFM Bragg peak intensities identify the magnetic structure as the $Γ_{10}$ representation, consisting of in-plane Dy moments stacked along the \cc{} axis in a $++--$ sequence. The magnetic structure is therefore identical to that previously reported for SmCuAs$_2$. Comparison among DyCuAs$_2$, SmCuAs$_2$, and GdCuAs$_2$ suggests that in-plane AFM order and the associated magnetic frustration on the tetragonal lattice are closely connected to the emergence of the resistivity minimum in the \RE{}CuAs$_2$ family. At the same time, the enhanced lattice response and stronger magnetic-field sensitivity observed in DyCuAs$_2$ imply that magnetoelastic and spin-orbit interactions additionally play important roles in determining the robustness of this anomalous transport behavior.