Theory of spin pumping through an interacting quantum dot tunnel coupled to a ferromagnet with time-dependent magnetization
We investigate two schemes for pumping spin adiabatically from a ferromagnet through an interacting quantum dot into a normal lead, which exploit the possibility to vary in time the ferromagnet's magnetization, either its amplitude or its direction. For this purpose, we extend a diagrammatic real-time technique for pumping to situations in which the leads' properties are time dependent. In the first scheme, the time-dependent magnetization amplitude is combined with a time-dependent level position of the quantum dot to establish both a charge and a spin current. The second scheme uses a uniform rotation of the ferromagnet's magnetization direction to generate a pure spin current without a charge current. We discuss the influence of an interaction-induced exchange field on the pumping characteristics.