The effect of pinhole formation/growth on the tunnel magnetoresistance of MgO-based magnetic tunnel junctions

In this study, we focus on how the formation and enlargement of metallic pinholes in MgO barriers (induced by large electrical currents) affect the tunnel magnetoresistance (TMR) of low and high resistance (R) magnetic tunnel junctions. The junctions were deposited by physical vapor deposition with barrier thicknesses of either 0.75 or 1.35 nm. For the parallel state, temperature-dependent R(T) measurements readily revealed a metallic conductance in the low-R sample, indicating that pinholes are already present in its thin barrier; a slight R(T) decrease with increasing temperature is observed for the high-R junction. After applying large current pulses to the low-R sample, we observe that the initially small R-decrease (similar to 6%) is accompanied by a significant TMR increase (similar to 20% at 20 K). Higher applied electrical currents continue to decrease R, leading to a gradual but steady TMR decrease. In contrast, the high-R sample exhibits a sharp and immediate decrease in TMR as soon as the first pinhole is formed. The origin of these effects will be discussed in terms of a thermally induced improvement of the barrier/electrode interfaces and the possibility of a magnetoresistance mechanism occurring through the metallic pinholes. (c) 2009 American Institute of Physics. [doi:10.1063/1.3236512]