Negative TMR in magnetic tunneling junctions with Zr oxide barrier

The magnetic tunnel junctions (MTJs) were prepared on Si [001] by using magnetron sputtering system. The structures of the MTJs are Si/FeNi/Cu/FeMn/Co/barrier/Co/Cu were the barrier are hybrids: AlO/sub x//ZrO/sub x/ and ZrO/sub x//AlO/sub x/. AlO/sub x/ as a barrier was also studied for comparison. Negative tunneling magnetoresistance (TMR) was observed in MTJs using hybrid barrier. The TMR shows a strong asymmetric bias dependence and changes from 8% at around zero bias to -4% at a high bias. The negative TMR at high bias is due to not only the energy dependence of spin-DOS but also the barrier shape of the MTJs. The mechanism for the negative TMR at high bias is different from that responsible for the inverse TMR in low bias range.