  There exists a significant challenge in developing efficient magnetic tunnel
junctions with low write currents for non-volatile memory devices. With the aim
of analysing potential materials for efficient current-operated magnetic
junctions we have developed a multi-scale methodology combining the ab initio
calculations of spin-transfer torque with large-scale time-dependent
simulations using atomistic spin dynamics. In this work we introduce our
multi-scale approach including a discussion on a number of possible mapping
schemes the ab initio spin torques into the spin dynamics. We demonstrate this
methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin
torques are primarily acting at the interface between the Co free layer and
MgO. Using spin dynamics we then calculate the reversal switching times for the
free layer and the critical voltages and currents required for such switching.
Our work provides an efficient, accurate and versatile framework for designing
novel current-operated magnetic devices, where all the materials details are
take into account.
