  The magnetization dynamics of a synthetic antiferromagnet subject to a short
magnetic field pulse, has been studied by using a combination of
first-principles and atomistic spin dynamics simulations. We observe switching
phenomena on the time scale of tens of picoseconds, and inertia-like behavior
in the magnetization dynamics. We explain the latter in terms of a dynamic
redistribution of magnetic energy from the applied field pulse to other
possible energy terms, such as the exchange interaction and the magnetic
anisotropy, without invoking concepts such as inertia of an antiferromagnetic
vector. We also demonstrate that such dynamics can also be observed in a
ferromagnetic material where the incident field pulse pumps energy to the
magnetic anisotropy.
