Using density functional theory, effects of Na- and Cu-substituted layers on the spin-dependent electronic transport properties of Fe/ZnO/Fe magnetic tunnel junction based on zinc oxide barrier tunnel, with rock-salt crystalline structure, have been studied. In zero-bias voltage, conductance and tunneling magneto-resistance (TMR) ratio of structures are calculated. It is showed that substituted layers in the pristine junction greatly affect conductance and TMR ratio of this junction. The results indicated that Cu-substituted layer with reducing conductance of pristine structure in the antiparallel alignment configuration, and increasing its conductance in the parallel alignment, leads to a large TMR ratio, up to 1800%. Due to the large conductance of pristine and Cu-substituted devices in the parallel alignment, these structures would be very beneficial for experimental applications that require the spin-polarized current.
