  We investigate the thermoelectric properties of a quantum dot coupled to
ferromagnetic and superconducting electrodes. The combination of spin polarized
tunneling at the ferromagnetic-quantum dot interface and the application of an
external magnetic field that Zeeman splits the dot energy level leads to large
values of the thermopower (Seebeck coefficient). Importantly, the thermopower
can be tuned with an external gate voltage connected to the dot. We compute the
figure of merit that measures the efficiency of thermoelectric conversion and
find that it attains high values. We discuss the different contributions from
Andreev reflection processes and quasiparticle tunneling into and out of the
superconducting contact. Furthermore, we obtain dramatic variations of both the
magnetothermopower and the spin Seebeck effect, which suggest that in our
device spin currents can be controlled with temperature gradients only.
