NMR study of trialuminide intermetallics

Abstract

We present a systematic study of the ${\mathrm{DO}}_{22}$-structure trialuminide intermetallic alloys using ${}^{27}\mathrm{Al}$ NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on ${\mathrm{Al}}_3\mathrm{Ti}$, ${\mathrm{Al}}_3\mathrm{V}$, ${\mathrm{Al}}_3\mathrm{Nb}$, and ${\mathrm{Al}}_3\mathrm{Ta}$ have been identified. Knight-shift tensors were isolated by observation of quadrupole satellite lines and fitting to the central-transition powder patterns. The results are associated with the local electronic density of states for each crystallographic site. Universally small isotropic Knight shifts and long $T_1$’s are consistent with low Fermi-surface densities of states indicating the importance of Fermi-surface features for the phase stability of these alloys. Larger anisotropic Knight shifts occurring at aluminum site I indicate strong hybridization at this site, and the electric-field-gradient tensors confirm the strong $\mathrm{ab}$ plane bonding configuration. Local-moment magnetism is found in ${\mathrm{Al}}_3\mathrm{V}$, yet electrically this material appears very similar to the other ${\mathrm{DO}}_{22}$ aluminides.