  We present a model of the thermopower in a mesoscopic tunnel junction between
two ferromagnetic metals based upon magnon-assisted tunneling processes. In our
model, the thermopower is generated in the course of thermal equilibration
between two baths of magnons, mediated by electrons. We predict a particularly
large thermopower effect in the case of a junction between two half-metallic
ferromagnets with antiparallel polarizations, $S_{AP} \sim - (k_B/e)$, in
contrast to $S_{P} \approx 0$ for a parallel configuration.
