Phonon Scattering and Thermal Resistance Due to Spin Disorder

Abstract

The interaction of phonons with spin sites in the disordered or paramagnetic state is estimated. Each spin site is a two-level system, capable of absorbing and reemitting phonons of matching frequency. The level spacing of each site is randomly distributed owing to the spin-spin interaction between the site and its nearest spin neighbors. This results in a reduction of the mean free path for a broad frequency band of lattice waves. Two parameters enter the theory. The spin-phonon interaction energy governs the strength of the interaction at each site. The spin-spin interaction energy determines the width of the band of affected phonons. The latter parameter is related to the ordering temperature. The thermal resistance can be estimated at temperatures which are high enough for complete disorder.