Nuclear Magnetic Resonance in Metals. I. Broadening of Absorption Lines by Spin-Lattice Interactions

Abstract

Magnetic resonance line shapes and widths, their temperature dependence, and the conduction electron shifts in resonance frequency are reported for the metals Li⁷, Na²³, Al²⁷, Cu⁶³, Cu⁶⁵, Ga⁶⁹, Ga⁷¹, Rb⁸⁵, Rb⁸⁷, and Cs¹³³. The absorption lines in most of these metals are broader than predicted for nuclear magnetic dipolar broadening alone. We propose that the mechanism responsible for most, if not all, of this additional broadening is the interaction between the nuclear spins and the conduction electrons, which also determines the spin‐lattice relaxation time. Spin‐lattice relaxation times T₁ are estimated from the nondipolar broadening of the experimental absorption lines. These T₁ values compare favorably with available directly measured values and with approximate T₁ values obtained by Korringa's theory from the measured resonance shifts. In the case of lithium, a dipolar line‐width transition was observed at 255°K; this transition results from self‐diffusion, for which we determine an activation energy of 9.8±1 kcal/mole.