NMR Study of ThAl2: 27Al, Dipolar Doublet, Quadrupole, and Anisotropic Shift Interactions

The nuclear magnetic resonance spectra of powdered intermetallic compounds MX2 of the C32 (AlB2) structure type lend themselves to analysis and interpretation in terms of nuclear dipole doublet interaction, nuclear electric quadrupole, and anisotropic Knight shift interactions. Within the hexagonal plane of the C32 structure three Pake pairs may be formed with each of the X nearest neighbors. The observed doublets in the NMR spectra of X nuclei are of the Pake type when the magnetic moment of the N nuclear species is small. Examples are 11B in ZrB2 and TiB2 and 27Al in ThAl2. An extensive analysis of the ThAl2 NMR spectra is presented which yields values for the lowest pure quadrupole frequency νQ=230.5± 2.0 kHz and Knight shift parameters Kiso=(0.042± 0.003)% and Ksx=−(0.012± 0.003)% The nearest-neighbor distance obtained was in agreement with spacings determined by x-ray techniques.