Spin-flip electron-energy-loss spectroscopy in itinerant-electron ferromagnets: Collective modes versus Stoner excitations.

Abstract

The energy-dependent spin-flip cross section due to exchange collisions of electrons with the spin-polarized electrons of an itinerant-electron ferromagnet is expressed in terms of a two-particle correlation function. For large momentum of the incident electron it is proportional to the transverse spin susceptibility and it is dominated by collective modes (magnons). For incident momentum comparable to the Fermi momentum of the ferromagnet electrons a model calculation within the random-phase approximation shows that the cross section has a consistent contribution from spin-flip Stoner excitations even for very small momentum transfer. The Stoner part of the spectrum is found to be essentially free of Coulomb-interaction effects. Recent experimental results are discussed and compared with the predictions of the model. The possibility of measuring magnon dispersions by this technique is pointed out.