  Large heat currents are obtained in Co/Cu/Co spin valves positioned at the
middle of Cu nanowires. The second harmonic voltage response to an applied
current is used to investigate the effect of the heat current on the switching
of the spin valves. Both the switching field and the magnitude of the voltage
response are found to be dependent on the heat current. These effects are
evidence for a thermal spin transfer torque acting on the magnetization and are
accounted for by a thermodynamic model in which heat, charge and spin currents
are linked by Onsager reciprocity relations.
