Magnetic-field effect on sound propagation as a probe of electronic structure and electron interaction in an itinerant-electron ferromagnet.

Abstract

We carry out a systematic formulation and a model numerical calculation on the effect of a magnetic field on the sound velocity and attenuation of a ferromagnetic metal based on the Stoner model. We find the magnetic-field effect to be strongly exchange enhanced and to depend very sensitively on the details of the electronic structure, both above and below the Curie point ${\mathit{T}}_{\mathit{C}}$. According to our result, for T>${\mathit{T}}_{\mathit{C}}$ the magnetic-field effects on the sound velocity and attenuation are proportional to, respectively, ${\mathrm{\ensuremath{\chi}}}^{3}$ and ${\mathrm{\ensuremath{\chi}}}^{4}$, where \ensuremath{\chi} is the (Stoner) magnetic susceptibility, with coefficients very sensitively reflecting the electronic structure near the Fermi surface. We also obtain similar features of the magnetic-field effects for T${\mathit{T}}_{\mathit{C}}$; the magnetic-field effects reflect very sensitively the electronic structure and electron interaction of a ferromagnetic metal. The mechanism of such magnetic effect on sound is that the screening of the ion-ion interaction is affected by the (additional) spin splitting of the conduction electron bands induced by a magnetic field. These findings suggest that the magnetic-field effects on sound propagation can be a useful probe of the electronic structure and electron interaction of a metal, ferromagnetic one, in particular.