Interaction of nuclear spins with phonons in a dense paramagnetic insulator

A theory of high-temperature nuclear acoustic resonance (NAR) in a dense paramagnetic insulator is presented. First, by the use of a previously described diagrammatic technique, an equation of motion is derived and solved for the nuclear quadrupolar spin-correlation function in a dense paramagnet. From this function, the T= NAR line shape is calculated and found to be Lorentzian. The NAR linewidths resulting from this calculation are found to be within observable range in many cases. Expressions for the acoustic attenuation due to both the dynamic nuclear quadrupolar interaction and the phonon modulation of the hyperfine interaction are then derived in the high-temperature limit by a calculation of the phonon self-energy due to these processes. By the use of the calculated nuclear quadrupolar correlation function and previously determined electron and nuclear functions for the correlation functions which occur in the expressions for the attenuation, it is shown that the attenuation due to the second process has no resonant part, while the resonant part of the first process is of such a magnitude that the observation of room-temperature NAR in Rb85 and Rb87 in RbMnF3 and isomorphic compounds might be possible.