Complex impedance of a spin injecting junction

Theory of the ac spin injection from a ferromagnetic electrode into a normal conductor through a tunnel or Schottky contact is developed. Diffusion and relaxation of nonequilibrium spins results in a frequency-dependent complex impedance Z(ω) controlled by the spin relaxation rates and the resistances involved. Explicit expression for Z(ω) is presented. Experimental investigation of the frequency dependence of Z should allow measuring spin relaxation times in both conductors, their effective resistances, and also the parameters of the contact controlling the spin injection.