Size dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions

Abstract

Magnetic tunnel junctions are under active consideration owing to their applications including the potential next generations of spin transfer torque memories. In view of the high symmetry of the magnetic properties and of the high frequency of the system eigenexcitations, out-of-plane magnetized systems are thought to enable a faster and simpler spin-torque-induced switching process than the formerly used in-plane magnetized systems. Unfortunately, the lack of high frequency and low current switching experiments have precluded, so far, the assessment of the speed potential of perpendicular anisotropy systems at low junction dimensions. By time resolving the switching and evidencing its stochastic aspects at the nanosecond-scale, the authors here demonstrate that a complex dynamics happens and persists down to small sized elements with always a very strong asymmetry between the two switching directions. The reversal is explained by the complex interplay between the spatial profile of the stray field emanating from the fixed system of the tunnel junction and the constraint that the switching is preferably initiated from the device edge.