Resonant X-ray scattering study of diffuse magnetic scattering from the topological semimetals EuCd${}_2$As${}_2$ and EuCd${}_2$Sb${}_2$

We have investigated the magnetic correlations in the candidate Weyl semimetals EuCd${}_{2}P{n}_2$, ($Pn$=As, Sb) by resonant elastic X-ray scattering (REXS) at the Eu${}^{2+}$ $M_5$ edge. The temperature and field dependence of the diffuse scattering of EuCd${}_2$As${}_2$ provide direct evidence that the Eu moments exhibit slow ferromagnetic correlations well above the N'{e}el temperature. By contrast, the diffuse scattering in the paramagnetic phase of isostructural EuCd${}_2$Sb${}_2$ is at least an order of magnitude weaker. The FM correlations present in the paramagnetic phase of EuCd${}_2$As${}_2$ could create short-lived Weyl nodes.