Evolution of the magnetic properties in the antiferromagnet Ce₂RhIn₈ simultaneously doped with Cd and Ir

We report the evolution of the magnetic properties of ${Ce}_2{Rh}_{1-x}{Ir}_x{In}_{8-y}{Cd}_y$ single crystals. In particular, for ${Ce}_2{Rh}_{0.5}{Ir}_{0.5}{In}_8$ ($T_N=2.0K$) and ${Ce}_2{Rh}_{0.5}{Ir}_{0.5}{In}_{7.79}{Cd}_{0.21}$ ($T_N=4.2K$), we have solved the magnetic structure of these compounds using single-crystal neutron magnetic diffraction experiments. Taking the magnetic structure of the ${Ce}_2{RhIn}_8$ heavy-fermion antiferromagnet as a reference, we have identified no changes in the $q=\left(\frac{1}{2},\frac{1}{2},0\right)$ magnetic wave vector; however, the direction of the ordered Ce³⁺ moments rotates toward the $ab$ plane, under the influence of both dopants. By constraining the analysis of the crystalline electric field (CEF) with the experimental ordered moment's direction and high-temperature magnetic-susceptibility data, we have used a mean-field model with tetragonal CEF and exchange interactions to gain insight into the CEF scheme and anisotropy of the CEF ground-state wave function when Cd and Ir are introduced into ${Ce}_2{RhIn}_8$. Consistent with previous work, we find that Cd doping in ${Ce}_2{RhIn}_8$ tends to rotate the magnetic moment toward the $ab$ plane and lower the energy of the CEF excited states' levels. Interestingly, the presence of Ir also rotates the magnetic moment towards the $ab$ plane although its connection to the CEF overall splitting evolution for the y = 0 samples may not be straightforward. These findings may shed light on the origin of the disordered spin-glass phase on the Ir-rich side of the phase diagram and also indicate that the ${Ce}_{2}M{In}_8$ compounds may not follow exactly the same Rh-Ir CEF effects trend established for the ${Ce}_{2}M{In}_5$ compounds.