Spin current rectification from a spin-biased quantum dot

We compute the spin current rectification coefficient of a non-equilibrium quantum dot subject to a spin bias and an {\it ac} charge bias with small amplitude. As a function of the position of the resonant level the spin current rectification coefficient shows a set of three peaks around the gate voltage at which the resonant or the upper level of the dot is in the vicinity of the equilibrium Fermi level in the leads. The peak heights can be related to the average number of the quantum dot electrons. We discuss the frequency dependence of the spin current rectification coefficient as well and emphasize the effects of the photon-assisted spin transport through the dot.