Resonant x-ray scattering study of magnetic ordering due to Fermi-surface nesting in ${\mathrm{SmNi}}_2{\mathrm{Ge}}_2$

We report the results of x-ray resonant scattering studies of samarium nickel germanide $\left({\mathrm{SmNi}}_2{\mathrm{Ge}}_2\right)$ compound. We confirm that the magnetic structures of this material are in accordance with Fermi-surface nesting as was hypothesized earlier. ${\mathrm{SmNi}}_2{\mathrm{Ge}}_2$ orders in an incommensurate antiferromagnetic (AF) structure characterized by a single propagation vector $\mathbf{q}{=(0,0,q}_z).\mathrm{}$ The value of $q_z$ is temperature dependent and approaches ∼0.775 r.l.u. near $T_N=17.7\mathrm{}\mathrm{K}.$ Below $T_t=11.8\mathrm{}\mathrm{K},$ the AF structure is characterized by $q_z=0.79\mathrm{}\pm 0.002,$ indicating a long-period-ordered phase. Ordered moments are confined to the basal plane in both the phases, as evidenced by the Q dependence of the magnetic-peak intensities. The temperature dependence of the magnetic structures is consistent with the “superzone” gap theory. In addition, a strong quadrupolar resonance below the Sm $L_{\mathrm{III}}$ edge was observed and compared to recent theoretical work.