Thermo-spin effects in quantum dots connected to ferromagnetic leads*

We study a system composed of a quantum dot in contact with ferromagnetic leads held at different temperatures, which we suggest can be used as a source of spin-voltage. Spin analogs to the thermopower and thermoelectric figure of merit are defined and studied as a function of junction parameters. It is shown that in contrast to bulk ferromagnets, the spin thermopower coeffcient in a junction can be as large as the Seebeck coefficient, resulting in a large spin figure of merit. In addition, it is demonstrated that the junction can be tuned to supply only spin current but no charge current. We also discuss experimental systems where our predictions can be verified.