NMR in solids: Thermodynamic effects of a pair of rf pulses on a system with two spin species

Abstract

NMR pulse experiments performed simultaneously on ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ in a LiF crystal, provide a quantitative verification of various theoretical predictions about relations between the Zeeman and dipolar components of the free-induction-decay signals, and the efficiency of transfer of Zeeman order into dipolar order by a phase-shifted pulse pair. An internal relaxation time of about 400 μsec is observed on the dipolar subsystem when the field is along the [111] direction. An interpretation is proposed for this "slow" approach to internal equilibrium.