Physical Theory of the Phonon Parallel Pump Instability

Abstract

Previous theories of the phonon parallel pump instability, based on equations of motion for the coupled magnon‐phonon system, have been very complicated and have not revealed the underlying physical phenomena. In this paper the steps in a simple, physically understandable, energy flow theory are outlined by means of a sample calculation which yields all of the principal results of the earlier calculations. In its most general development, this theory can be applied to any phonon wave vector for any direction and magnitude of applied static magnetic field. It can include the effects of magnetic, elastic, and magnetoelastic anisotropy. Moreover, the physical basis of the theory makes many conclusions possible without the necessity of detailed calculations.