Verification of Transition State Theory by Landau-Lifshitz Simulation

Most switching rate theory (including spin-torque switching) has relied implicitly on the Transition State Theory used in chemical rate theory, since Arrhenius-Neel-type formulas are based on this assumption. However, this theory has never been checked against Landau-Lifshitz-Gilbert simulation. Pieter Visscher and a graduate student, Shuxia Wang, have done this [Shuxia Wang and P. B. Visscher, “Switching rate of MRAM element: verifying transition state theory”, accepted 11/05 by J. Applied Physics (Paper CV-05, MMM05)]. This required developing algorithms for identifying and counting switches in a simulation context. The calculated rates for parameters corresponding to an MRAM element are shown in the figure, as a function of the Landau-Lifshitz damping parameter  – the transition state theory works very well for this type of system. Although the barrier used in this simulation is low (KV/kBT = 5.1), the method can be applied to extract corrections to the Transition State Theory in systems with high barriers.