Enhanced nuclear acoustic resonance: some theoretical considerations

Abstract

The resonant interchange of quanta between a magnetic spin system and a phonon system gives rise both to acoustic magnetic absorption and to spin-lattice relaxation by the ‘direct process’. A simple relation between the two is followed by a summary of the hierarchy of acoustic interactions with a spin system for both Kramers and non-Kramers ions. Systems with J = 3/2 and 2 in tetragonal symmetry are used as model examples, with no loss of generality. Matrix elements of the spin-strain hamiltonian are derived, with special reference to enhanced nuclear magnetic systems. Mechanisms involving both magnetic dipole (md) and electric quadrupole (eq) hyperfine interactions are included. Special reference is made to crystals such as HoVO 4 and PrVO 4 containing the nuclei 165 Ho ( I = 7/2) and 141 Pr ( I = 5/2), but the theory applies to a range of lanthanide nuclei of ions in sites of tetragonal symmetry.