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.

• Received 12 July 2010

DOI:https://doi.org/10.1103/PhysRevB.82.165334