Nuclear Magnetic Resonance in theLaX3Intermetallic Compounds

Abstract

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\ifmmode^\circ\else\textdegree\fi{}K. The isotropic and anisotropic ${\mathrm{Pb}}^{207}$ Knight shifts were measured at 1.5, 4.2, and 77 \ifmmode^\circ\else\textdegree\fi{}K and ${T}_{1}$ was measured at 1.55\ifmmode^\circ\else\textdegree\fi{}K. Also presented are measurements of the La ${T}_{1}$ in La${\mathrm{In}}_{3}$ from 1.5 to 300\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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 (${T}_{1}T=0.59$ sec \ifmmode^\circ\else\textdegree\fi{}K at 4.2\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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 $3{K}_{\mathrm{ax}}=+0.43%$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K) are nearly temperature independent. The Pb relaxation time in La${\mathrm{Pb}}_{3}$ (${T}_{1}T=63\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ sec\ifmmode^\circ\else\textdegree\fi{}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 susceptibility and that exchange-enhancement effects are probably not important. For La${\mathrm{Pb}}_{3}$, $d$-orbital effects are less important than the $d$-spin contributions. In all three compounds the La $d$-spin contributions to the NMR properties and the bulk susceptibility are of similar magnitude.