Thermally activated switching of small magnetic tunnel junctions

Small magnetic tunnel junctions were prepared and the magnetization reversal of their free layers was studied by applying high-speed reversal fields driven by pulsed currents. From the decay of the switching field with the number of pulses or the pulse length the thermal activation energy was deduced. Large cells (width>150 nm) showed a significant lower activation energy than expected from single-domain-theory, indicating non-uniform switching. Small cells (width ∼ 90 nm and length 150 to 200 nm) could be well described by Stoner-Wohlfarth single domain model and single step switching with Arrhenius activation energy. For scaling of magnetic random access memories down to 100 nm this would indicate that a smaller free layer volume is to a large degree compensated by higher relative activation energy due to more uniform switching.