Microscopic and Macroscopic Electronic Properties of the Au${\mathrm{Cu}}_3$-Type Alloys: The La${\mathrm{Sn}}_3$-La${\mathrm{In}}_3$ Pseudobinary Alloy System

The bulk properties of the ${\mathrm{LaSn}}_{3x}{\mathrm{In}}_{3(1-x)\mathrm{}}$ and similar alloy systems display a dramatic, somewhat oscillatory, dependence on the valence-electron concentration. For the ${\mathrm{LaSn}}_{3x}{\mathrm{In}}_{3(1-x)\mathrm{}}$ alloy system we have studied the dependence on $x$ of the magnetic susceptibility $\chi$ and the local electronic behavior at the La and Sn-In sites using the ${\mathrm{La}}^{139}$ and ${\mathrm{Sn}}^{119}$ nuclear-magnetic-resonance Knight shifts $K$ and spin-lattice relaxation times $T_1$. These results are compared with those for the superconducting transition temperature $T_c$, the electronic-specific-heat coefficient $\gamma$, and the Debye temperature ${\Theta }_D$. Using McMillan's strong-coupling model we have calculated from $\gamma$ and $\frac{T_c}{{\Theta }_D}$, the electron-phonon coupling parameter $\lambda$, the bare density of states $N\left(0\right)\mathrm{}$, and the electron-phonon interaction strength $V$. For the NMR measurements, the Sn NMR properties follow the behavior of the bulk density of states at the Fermi energy, $N\left(0\right)\mathrm{}$, considerably better than do the La NMR properties suggesting that the local electronic properties of the Sn-In sites play the dominant role in determining $T_c$. Analysis of the La NMR and $\chi$ behavior with $x$ indicates the paramagnetic susceptibility of these alloys arises from the La $d$ band with the La $d$-orbital contribution accounting for most of the large susceptibility for $x$ near La${\mathrm{Sn}}_3$ and La${\mathrm{In}}_3$.