Nuclear Magnetic Resonance in Cubic Equiatomic Group-VIII Aluminides

Abstract

Nuclear-magnetic-resonance measurements are reported for the seven cubic equiatomic group-VIII aluminides: FeAl, RuAl, OsAl, CoAl, RhAl, IrAl, and NiAl. The ${\mathrm{Al}}^{27}$ resonance was studied in each compound and that of ${\mathrm{Co}}^{59}$ in CoAl. The Knight shift, nuclear spin-lattice relaxation rate, linewidth, and intensity were determined at temperatures in the range 4.2-300\ifmmode^\circ\else\textdegree\fi{}K and at 8 and 12 MHz. Except for FeAl, the ${\mathrm{Al}}^{27}$ shifts are much less in magnitude than that of pure Al, and the spin-lattice relaxation times ${T}_{1}$ are 10 to 500 times greater than that of pure Al. ${T}_{1}T$ is relatively constant around room temperature, but in each case decreases below about 77\ifmmode^\circ\else\textdegree\fi{}K. An exceptional behavior is observed for ${\mathrm{Al}}^{27}$ in CoAl, where there is an additional contribution to the relaxation rate independent of temperature from 4.2 to 300\ifmmode^\circ\else\textdegree\fi{}K. This is believed to be due to the presence of localized magnetic moments. In every case the linewidth exceeds the theoretical nuclear dipolar width and, while intensity measurements indicate that all transitions of all nuclei contribute to the observed signals, there is distinct evidence of quadrupolar effects. The Knightshift and ${T}_{1}$ results imply that the $s$ character of the conduction electrons is small at Al sites. This is shown to be in accord with the Engel-Brewer model of intermediate phases in alloy systems.