Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

Resonant tunneling through states in the barrier of a magnetic tunnel junct ion has been analyzed theoretically for the case of a spin-polarized densit y of barrier states. It is shown thai for highly spin-polarized barrier sta tes, the magnetoresistance due to resonant tunneling is enhanced compared t o the magnetoresistance due to direct tunneling between the ferromagnetic e lectrodes. Moreover, it is predicted that whenever the barrier states have a nonzero polarization, tunneling magnetoresistance exists even if only one electrode is magnetic, while the other is not. The above effects have been studied for arbitrary location of the states. In particular, we consider t he case of a thin sheet of magnetic dopants in close proximity to and coupl ed ferromagnetically or antiferromagnetically to one of the electrodes. Dep ending on the dopant polarization, the distance to the electrode and the ty pe of coupling, the total magnetoresistance can be enhanced or reduced, and may be reversed for antiferromagnetic coupling.