Relativistic theory of magnetic inertia in ultrafast spin dynamics

Abstract

In the field of ultrafast spin dynamics, magnetic inertia (spin nutation) is considered to hold great promise for achieving ultrafast magnetization switching. However, the fundamental origin of magnetic inertial dynamics is unknown. Here, the authors derive a complete theory of spin dynamics, including magnetic inertia, from fundamental Dirac theory. They show that magnetic inertia exists for any single Dirac particle and that it is a higher-order relativistic spin-orbit coupling effect compared to Gilbert damping. Magnetic inertia is therefore expected to play a role only on an ultrashort subpicosecond timescale.