Magnetization switching in nanoelements induced by the spin-transfer torque: Study by massively parallel micromagnetic simulations

In this paper we present a detailed numerical study of magnetization switching in shape-anisotropic thin-film nanoelements. These elements are at present of the major interest for the applied solid state magnetism as main components of a new generation of conventional and spin-transfer-torque (STT) magnetic random access memory (MRAM) cells. To conduct this study, we have developed a highly efficient method for massively parallel micromagnetic simulations of the magnetization reversal in small-size nanoelements, which allows to fully exploit the large performance gain available on the GPU architecture (usually achievable only for large systems). We apply our method to the spin-torque-induced magnetization switching in elliptical nanoelements in presence of thermal fluctuations. Being able to compute simultaneously the reversal of up to 1000 such elements, we obtain the dependence of (i) the average switching time and (ii) the distribution density of switching times for individual elements on the element size with a high statistical accuracy. Analysis of these dependencies provides important insights into the physics of magnetization reversal in such systems. Comparison with analogous simulations in the macrospin approximation allows to determine the validity limits of the macrospin model. Our methodology can be applied for the optimization of the MRAM design regarding the information life time and significantly improve the prediction accuracy of write and read error rates of conventional and STT-based MRAM cells.