  We compute thermal spin transfer torques (TST) in Fe-MgO-Fe tunnel junctions
using a first principles wave function-matching method. At room temperature,
the TST in a junction with 3 MgO monolayers amounts to 10^-7J/m^2/K, which is
estimated to cause magnetization reversal for temperature differences over the
barrier of the order of 10 K. The large TST can be explained by multiple
scattering between interface states through ultrathin barriers. The angular
dependence of the TST can be very skewed, possibly leading to thermally induced
high-frequency generation.
