Spin effects in electron tunneling through a quantum dot coupled to noncollinearly polarized ferromagnetic leads

Spin-dependent transport through an interacting single-level quantum dot coupled to ferromagnetic leads with noncollinear magnetizations is analyzed theoretically. The transport properties and average spin of the dot are investigated within the nonequilibrium Green function technique based on the equation of motion in the Hartree-Fock approximation. Numerical results show that Coulomb correlations on the dot and strong spin polarization of the leads significantly enhance precession of the average dot spin around the effective molecular field created by the external electrodes. Moreover, they also show that spin precession may lead to negative differential conductance in the voltage range between the two relevant threshold voltages. Nonmonotonous angular variation of electric current and change in sign of the tunnel magnetoresistance are also found. It is also shown that the diodelike behavior in asymmetrical junctions with one electrode being half-metallic is significantly reduced in noncollinear configurations.