Optimal control of magnetization reversal in a monodomain particle by means of applied magnetic field

G. J. Kwiatkowski, M. H. A. Badarneh, D. V. Berkov, P. F. Bessarab

Published 2020-04-05Version 1

A complete analytical solution to the optimal reversal of a macrospin with easy-axis anisotropy is presented. Optimal control path (OCP) minimizing the energy cost of the reversal is identified as a function of the switching time, anisotropy strength and damping parameter. Time-dependent direction and amplitude of the optimal switching field are derived directly from the calculated OCP. The minimum energy cost of the reversal as a function of the switching time is characterized by two asymptotic regimes. It scales inversely with the switching time for fast switching, follows an exponential asymptotics for slow switching and reaches the lower limit proportional to the energy barrier between the target states and to the damping parameter at infinitely long switching time. For a given switching time, the energy cost of the reversal can never be smaller than that for a free macrospin. This limitation can be bypassed by adding a hard anisotropy axis which activates internal torques in the desired switching direction, thereby significantly reducing the energy cost.