We study the nonequilibrium spin current through a quantum dot consisting of two localized spins $\frac{1}{2}$ coupled to two ferromagnetic insulators. The influence of an intradot magnetic field and exchange coupling, different dot-reservoir coupling configurations, and the influence of magnon chemical potential differences vs magnetic field gradients onto the spin current are examined. We discuss various spin switching mechanisms and find that, in contrast to electronic transport, the spin current is very sensitive to the specific coupling configuration and band edges. In particular, we identify one- and two-magnon transport processes which can lead to resonances and antiresonances for the spin current.

• Received 30 June 2005

DOI:https://doi.org/10.1103/PhysRevB.72.165343