Magnetotransport properties of CoFeB/MgO/CoFe/MgO/CoFeB double barrier magnetic tunnel junctions with large negative magnetoresistance at room temperature

CoFeB/MgO/CoFe/MgO/CoFeB double-barrier magnetic-tunnel junctions were fabricated using an ultrahigh vacuum magnetron sputtering system, and their magnetotransport properties were characterized at room temperature. After post-deposition annealing, the polarity of TMR changed from negative to positive with increasing bias voltage. A relatively high negative TMR ratio of 30% was obtained at a negative bias voltage. Furthermore, a unique bias voltage dependence of conductance was observed at room temperature. This behavior may be attributable to the large minority density of states caused by the interfacial oxidation of the middle CoFe layer.