Local Electronic Environment of Protons in VH_x Alloys: Knight Shift and T₁ of Proton NMR

Abstract

The Knight shift (K_H) and the spin-lattice relaxation time T₁, of protons have been measured in vanadium-hydrogen alloys (VH_x) with hydrogen concentration x=0.042∼0.736, at temperatures between 100° and 200°C. The resolution of ±1 ppm in the shift was attained by using a high-resolution spectrometer, and the effect of demagnetizing field was isolated by using a single sheet of foil as a specimen. This allowed the simultaneous determination of K_H and the bulk magnetic susceptibility. K_H measured relative to bare protons was found to be negative and change little with hydrogen concentration. No temperature dependence of the shift was observed, even across the phase transition. These results are interpreted in terms of a contact interaction with the uniform spin-polarization in the interstitial region and some additional contributions from H-induced states. An evidence for the electron-electron interaction in VH_x is derived from comparison of K_H and T₁.