Nuclear Magnetic Resonance in theLaX3Intermetallic Compounds

The ${\mathrm{La}}^{139}$ nuclear-magnetic-resonance (NMR) Knight shift and spin-lattice relaxation time ($T_1$) in La${\mathrm{Pb}}_3$ were measured from 1.5 to 300°K. The isotropic and anisotropic ${\mathrm{Pb}}^{207}$ Knight shifts were measured at 1.5, 4.2, and 77 °K and $T_1$ was measured at 1.55°K. Also presented are measurements of the La $T_1$ in La${\mathrm{In}}_3$ from 1.5 to 300°K which are more complete than previously reported. These measurements are compared with previously reported measurements for La${\mathrm{Sn}}_3$. The ${\mathrm{La}}^{139}$ Knight shift (+0.010% at 4.2°K) in La${\mathrm{Pb}}_3$ has a temperature dependence roughly five times that found in La${\mathrm{Sn}}_3$ and La${\mathrm{In}}_3$ even though the bulk susceptibility is considerably smaller. For La${\mathrm{Pb}}_3$, the La $T_{1}T$ product is nearly temperature independent ($T_{1}T=0.59\mathrm{}$ sec °K at 4.2°K) and is about half that found in La${\mathrm{Sn}}_3$. For La${\mathrm{In}}_3$, $T_{1}T$ increases by 50% between 1.5 and 300°K and has a temperature dependence similar to La${\mathrm{Sn}}_3$. The isotropic and anisotropic Pb Knight shifts ($K_{\mathrm{iso}}=+0.70\%$ and $3K_{\mathrm{ax}}=+0.43\%$ at 4.2°K) are nearly temperature independent. The Pb relaxation time in La${\mathrm{Pb}}_3$ ($T_{1}T=63\mathrm{}\times {10}^{-4\mathrm{}}$ sec°K) is about four times faster than in Pb metal, indicating a larger $s$-contact contribution than in Pb metal and a large negative Knight-shift component. The La NMR and bulk-susceptibility data are partitioned using the customary approximation for transition metals. We find the results for La${\mathrm{In}}_3$ and La${\mathrm{Sn}}_3$ are quite similar suggesting that in both these materials the La $d$-orbital susceptibility is much larger than the $d$-spin...