Magnons in Ferromagnetic Films
Abstract
The theory of magnons in ferromagnetic films has important applications to real magnets and a rather long history. In this dissertation, we first present a new version of the asymptotically exact theory of the spectrum and transverse distribution of magnetization in long-wave magnons. It is based on the exact analytical solution of the linearized Landau-Lifshitz equation in a film. We also studied and used symmetry of the Hamiltonian. Our new method simplifies all calculations and provides analytical results for the range of parameters most important for experiment. The quantization of the transverse wave vector and the role of evanescent waves at different values of parameters are studied. Another important motivation of this work was its application to the problem of Bose-Einstein condensation (BEC) and superfluidity of magnons. We use a classical modification of the Holstein-Primakoff transformation to solve the Landau-Lifshitz equation, the exact phase diagram for magnon condensate in Yttrium Iron Garnet Film is studied. We also collaborated with an experimental group that provides direct experimental evidence that magnons in a condensate exhibit a repulsive interaction resulting in condensate stabilization. We propose a mechanism, which is responsible for the interaction inversion. This mechanism supports their conclusions by the theoretical model based on the Gross-Pitaevskii equation.
Subject
magnonCitation
Li, Gang (2020). Magnons in Ferromagnetic Films. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192682.