Relaxation phenomena in current-induced switching in thin magnetic tunnel junctions

Recently, reversible resistance (R) changes were observed in thin tunnel junctions (TJ) when a critical electrical current was applied. These changes are called current-induced switching (CIS) and are attributed to electromigration in nanoconstrictions in the insulating barrier. Here, we study the CIS effect on a thin TJ prepared by IBD, displaying a 3.4% R change when a CIS cycle is performed at room temperature. After complete (or half) CIS cycles with adequate maximum currents, we monitored R as a function of time. In both cases a non-monotonic relaxation occurs with two distinct relaxation times, τ1∼10min, τ2∼102min. First R increases (decreases) rapidly, but then a slow relaxation dominates, reducing (increasing) R. These opposite relaxation processes suggest two independent physical mechanisms acting simultaneously inside the TJ. The physical origin of these effects is discussed.