Theory of Ultrasonic Spin Echoes

Abstract

A theory of ultrasonic spin echoes valid for arbitrary spin is presented. Semiclassical vector-model equations are constructed for components of the dipole and quadrupole moment tensors which are excited by ultrasonic pulses in analogy with the well-known Bloch equations. The echo amplitudes are found to depend on the wave number of the pulse, the crystal length, spin density, sound velocity, the density of the medium as well as the magnitude of the appropriate macroscopic dipole or quadrupole moment. Our numerical estimates for a number of physical systems indicate that ultrasonic-spin-echo experiments are feasible for a variety of nuclear and electronic spin systems.