Wave–particle interactions in a spin polarized plasma

We study the interplay between electrons and spin waves (magnons) in a ferromagnetic material, using an augmented Vlasov–Poisson model that includes the electron spin dynamics. The ions are fixed, but their spins can evolve in time on the unit sphere according to the Landau–Lifshitz equation, which includes nearest-neighbor magnetic interactions. The two components interact not only through the electrostatic Coulomb force, but also via magnetic-exchange interaction terms. The linear response analysis reveals the existence of a wave–particle resonance occurring at the frequency of the magnons. This resonance gives rise to significant energy exchange between the magnons and the electrons, resulting in a rapid loss of the localized magnetism, which is analogous to the ultrafast demagnetization observed in experiments on thin ferromagnetic films. Depending on the initial electronic spin polarization, the resonance can lead to either damping or instability of the wave. These results show that wave–particle effects, similar to those frequently encountered in plasma physics, may play a key role in spin-polarized plasmas and electron beams.