Magnon radiation by moving Abrikosov vortices in ferromagnetic superconductors and superconductor-ferromagnet multilayers

Abstract: In systems combining type-II superconductivity and magnetism the non-stationary magnetic field of moving Abrikosov vortices may excite spin waves, or magnons. This effect leads to the appearance of an additional damping force acting on the vortices. By solving the London and Landau-Lifshitz-Gilbert equations we calculate the magnetic moment induced force acting on vortices in ferromagnetic superconductors and superconductor/ferromagnet superlattices. If the vortices are driven by a dc force, magnon generation due to the Cherenkov resonance starts as the vortex velocity exceeds some threshold value. For an ideal vortex lattice this leads to an anisotropic contribution to the resistivity and to the appearance of resonance peaks on the current voltage characteristics. For a disordered vortex array the current will exhibit a step-like increase at some critical voltage. If the vortices are driven by an ac force with a frequency \omega, the interaction with magnetic moments will lead to a frequency-dependent magnetic contribution \eta_M to the vortex viscosity. If \omega is below the ferromagnetic resonance frequency \omega_F, vortices acquire additional inertia. For \omega > \omega_F dissipation is enhanced due to magnon generation. The viscosity \eta_M can be extracted from the surface impedance of the ferromagnetic superconductor. Estimates of the magnetic force acting on vortices for the U-based ferromagnetic superconductors and cuprate/manganite superlattices are given.