  We present a theoretical analysis of the nonlinear bias and temperature
dependence of current-voltage characteristics of a spin-valve device which is
formed by connecting a quantum dot to two ferromagnetic electrodes whose
magnetic moments orient at an angle $\theta$ with respect to each other. The
theory is based on nonequilibrium Green's function approach and focused on
current perpendicular to plane geometry. Coulomb interaction has been taken
into account explicitly at the Hartree level. We derive a formula in closed
form for current flowing through the device in general terms of bias and
temperature. In the wideband limit we report exact results for the TMR junction
nonlinear I-V curve as a function of $\theta$. We also report the conductance
slope at zero bias as a function of temperature for which experimental results
reported an anomalous behavior.
