Nuclear magnetic resonance of47Ti and49Ti in hexagonal close-packed titanium metal

Abstract

The nuclear magnetic resonance of 47Ti and 49Ti has been observed in hexagonal close-packed titanium metal. Measurements of the spin-echo profile were carried out at 4.2K at various frequencies around 10 MHz by means of the pulsed nuclear resonance technique between about 40 and 50 kG. Because both 47Ti and 49Ti possess a nuclear quadrupole moment, the spectra of both isotopes show a satellite structure, which is typical of quadrupole-disturbed nuclear magnetic resonance. Since the gyromagnetic ratios of 47Ti and 49Ti are nearly identical, the resonances of the two isotopes were superimposed, leading to rather complex experimental spectra. By computer simulation of the experimental spectra, however, the quadrupole interaction and Knight shift parameters could be determined quite accurately. The deduced quadrupole frequencies for 47Ti and 49Ti are in full accordance with the ratio of the quadrupole momenta of the two isotopes and lead to an electric field gradient of 1.62+or-0.08*1017 V cm-2 for hexagonal close-packed titanium metal. The isotropic and axial Knight shifts are found to be 0.21+or-0.02% and 0.01+or-0.02%, respectively. Although these values could be reproduced quite reasonably by theoretical estimations based on recent band-structure calculations, these estimations indicate that the partitioning of the Van Vleck contribution to the Knight shift into a hyperfine field and Van Vleck susceptibility is only a poor approximation to the exact expression for the Van Vleck term.