Evolution of the partially frustrated magnetic order in CePd$_{1-x}$Ni$_x$Al

We report on a single-crystal neutron diffraction study of the evolution of the antiferromagnetic order in the heavy-fermion compound CePd$_{1-x}$Ni$_x$Al which exhibits partial geometric frustration due to its distorted Kagome structure. The magnetic structure is found to be unchanged with a propagation vector $Q_mathrm{AF} approx (0.5~0~0.35)$ for all Ni concentrations $x$ up to $x_c approx 0.14$. Upon approaching the quantum critical concentration $x_c$, the ordered moment vanishes linearly with Neel temperature $T_{rm N}$, in good agreement with CePdAl under hydrostatic pressure. For all Ni concentrations, substantial short-range magnetic correlations are observed above $T_{rm N}$ as a result of frustration.