  Laser induced ultrafast demagnetization is the process whereby the magnetic
moment of a ferromagnetic material is seen to drop significantly on a timescale
of $10-100$s of femtoseconds due to the application of a strong laser pulse. If
this phenomenon can be harnessed for future technology, it offers the
possibility for devices operating at speeds several orders of magnitude faster
than at present. A key component to successful transfer of such a process to
technology is the controllability of the process, i.e. that it can be tuned in
order to overcome the practical and physical limitations imposed on the system.
In this paper, we demonstrate that the spin-orbit mediated form of ultrafast
demagnetization recently investigated [arXiv:1406.6607] by ab-initio
time-dependent density functional theory (TDDFT) can be controlled. To do so we
use quantum optimal control theory (OCT) to couple our TDDDT simulations to the
optimization machinery of OCT. We show that a laser pulse can be found which
maximizes the loss of moment within a given time interval while subject to
several practical and physical constraints. Furthermore we also include a
constraint on the fluence of the laser pulses and find the optimal pulse that
combines significant demagnetization with a desire for less powerful pulses.
These calculations demonstrate optimal control is possible for spin-orbit
mediated ultrafast demagnetization and lay the foundation for future
optimizations/simulations which can incorporate even more constraints.
