Temperature and bias voltage dependence of Co-Fe-AlO/sub x/-Py-AlO/sub x/-Co-Fe double-barrier junctions

Exchange-biased magnetic tunnel junctions with single and double barriers are investigated with respect to the temperature and bias voltage dependence of the tunneling magnetoresistance. The single-barrier junctions show a tunneling magnetoresistance ratio of up to 49% at room temperature (72% at 10 K), the double-barrier systems up to 38% (57%), respectively, with three clearly separated magnetic states. The temperature and bias voltage dependence of the double-barrier junctions is explained as a serial connection of two single junctions. Theoretical studies of the tunneling magnetoresistance exhibit that the magnetoresistance ratio can be enhanced by ballistic electrons in double-barrier junctions, but only if the potential of the middle electrode can be shifted.