Time-Resolved Studies of the Spin-Transfer Reversal Mechanism in Perpendicularly Magnetized Magnetic Tunnel Junctions

Pulsed spin-torque switching has been studied using single-shot time-resolved electrical measurements in perpendicularly magnetized magnetic tunnel junctions as a function of pulse amplitude and junction size in 50 to 100 nm diameter circular junctions. The mean switching time depends inversely on pulse amplitude for all junctions studied. However, the switching dynamics is found to be strongly dependent on junction size and pulse amplitude. In 50 nm diameter junctions the switching onset is stochastic but the switching once started, is fast; after being initiated it takes less than 2 ns to switch. In larger diameter junctions the time needed for complete switching is strongly dependent on the pulse amplitude, reaching times less than 2 ns at large pulse amplitudes. Anomalies in the switching rate versus pulse amplitude are shown to be associated with the long lived (> 2 ns) intermediate junction resistance states.

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