Generating spin current by AC magnetic field

We report a theoretical investigation on the possibility of generating pure spin current without an accompanying charge current, by applying a train of magnetic field pulses on the leads of a tunnel junction. When the duration of on-state of the pulse is shorter than the spin relaxation time while the off-state is longer than it, a spin current is driven through the two-probe device coherently. The time averaged spin current is found to be almost a periodic function of the pulse strength. A negative spin current can also be produced for a positive spin chemical potential, due to quantum interference among the Fourier modes of the photon assisted tunneling.