Magnetic properties ofCeSb1−xTexsolid solutions

We report magnetic properties of $\mathrm{Ce}{\mathrm{Sb}}_{1-x}{\mathrm{Te}}_x$ solid solutions in the whole range of composition $0<x<\mathrm{}1\mathrm{}$. We find that a simple Heisenberg interaction treated in the molecular-field approximation is sufficient to describe the experimental results at $x>\mathrm{}0.05\mathrm{}$. In particular, a linear $x$ dependence of the effective exchange-coupling constants ${\overline{\Gamma }}_1$ and ${\overline{\Gamma }}_2$ between nearest and next-nearest neighbors, respectively, accounts for the nonlinear behavior of the variations of the Néel temperature $T_N\mathrm{}\left(x\right)\mathrm{}$ which goes through a minimum at $x\simeq 0.07$. This model, however, is too crude to account for the magnetic properties at concentrations $x<\mathrm{}0.05\mathrm{}$, such as a maximum of the crystal-field splitting energy $\Delta \mathrm{}\left(x\right)\mathrm{}$ between the ${\Gamma }_7$ and ${\Gamma }_8$ levels of the $4f$-electron states at $x\simeq 0.04$, a maximum of the paramagnetic Curie temperature ${\Theta }^{*}\mathrm{}\left(x\right)\mathrm{}$ at $x\simeq 0.02$, and a very strong monotonic decrease of $T_N\mathrm{}\left(x\right)\mathrm{}$ in the whole range $0<x<\mathrm{}0.05\mathrm{}$. To account for these experimental data, we have studied the fourth-order indirect exchange in the mixing parameter, derived after a canonical transformation of the Schrieffer-Wolff type is applied to the multisite Anderson model when both the crystal-field effects and the large spin-orbit coupling of the intermediate state of the Ce electron in the $4f$ subshell are taken into account. This model provides an overall understanding of the magnetic properties of $\mathrm{Ce}{\mathrm{Sb}}_{1-x}{\mathrm{Te}}_x$ solutions at all $x$. A detailed discussion of this model with respect to previous models is also reported.