Microscopic and macroscopic electronic properties of the AuCu3-type alloys: the LaSn3--LaIn3 pseudobinary alloy system

The bulk properties of the LaSn₃ₓIn₃₍₁₋ₓ₎ and similar alloy systems display a dramatic, somewhat oscillatory, dependence on the valence-electron concentration. For the LaSn₃ₓIn₃₍₁₋ₓ₎ alloy system we have studied the dependence on x of the magnetic susceptibility χ and the local electronic behavior at the La and Sn-In sites using the La¹³⁹ and Sn¹¹⁹ nuclear-magnetic-resonance Knight shifts K and spin-lattice relaxation times T₁. These results are compared with those for the superconducting transition temperature T_c, the electronic-specific-heat coefficient γ, and the Debye temperature ${\Theta }_D$. Using McMillan's strong-coupling model we have calculated from γ and $\frac{T_c}{{\Theta }_D}$, the electron-phonon coupling parameter λ, the bare density of states N(0), 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(0), 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 χ 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 LaSn₃ and LaIn₃.