Electric and thermoelectric phenomena in a multilevel quantum dot attached to ferromagnetic electrodes

Nonequilibrium Green's function formalism is used to study electron and energy transport in the Coulomb-blockade regime through a two-level quantum dot/molecule attached to ferromagnetic leads. Interplay between magnetic and thermoelectric properties is investigated in the nonlinear-response regime and strong spin effects in the nonlinear thermopower are found. Significant spin thermopower S(spin) can be generated in a relatively wide region of temperature difference Delta T. It is also shown that spin asymmetry due to presence of one half-metallic and one nonmagnetic electrodes plays an important role and strongly influences both charge and spin thermopower. S(spin) varies considerably, if the roles of both leads are interchanged. Spin thermopower is enhanced in the region of higher values of Delta T, if half-metallic electrode acts as an energy drain. On the other hand, in such a configuration, Pauli spin blockade occurs in electron transport.