Periodic inversion of tunneling magnetoresistance through Coulomb blockaded quantum dots

Green's function approach is used to study the tunneling magnetoresistance (TMR) through a nonmagnetic quantum dot, which is coupled asymmetrically to two ferromagnetic leads. We predict a remarkable oscillation effect of the TMR in both sign and magnitude. As the gate voltage varies, the TMR is inverted periodically at each Coulomb peak of conductance, and it retains the normal sign in the Coulomb blockade valleys. The magnitude of the inverse TMR can be tuned to be as large as that of the normal TMR. The oscillation effect is attributed to the quantizations of both electronic charge and energy in the dot.