Theory of spin filtering through quantum dots

Using a nonequilibrium diagram technique for Hubbard operator Green functions combined with a generalization of the transfer Hamiltonian formalism, we calculate the transport through a magnetic quantum dot system with spin-dependent couplings to the contacts. In specific regimes of the parameter space the spin-dependent tunnel current becomes more than 99.95% spin polarized, suggesting that a device thus constructed can be used in spin-filter applications. First-principles electronic structure calculations show the existence of nanostructured systems, such as, e.g., ${\mathrm{M}\mathrm{g}\mathrm{O}/\mathrm{F}\mathrm{e}/\mathrm{P}\mathrm{d}}_5/\mathrm{F}\mathrm{e}/\mathrm{M}\mathrm{g}\mathrm{O}$ (001), with the desired properties in the direction of the current.