  We report on the importance of resonant-tunneling processes on quantum
transport through interacting quantum-dot spin valves. To include Coulomb
interaction in the calculation of the tunneling magnetoresistance (TMR), we
reformulate and generalize the recently-developed, numerically-exact method of
iterative summation of path integrals (ISPI) to account for spin-dependent
tunneling. The ISPI scheme allows us to investigate weak to intermediate
Coulomb interaction in a wide range of gate and bias voltage and down to
temperatures at which a perturbative treatment of tunneling severely fails.
