Ab-initio description of all optical switching

By creating via pump laser pulse a non-equilibrium distribution of charge on sub-exchange time scales (i.e., faster than the time scale associated with spin flip in the ground state) we demonstrate that a precise control of magnetic structure is possible on ultra-short time scales, including switching of spin order from anti-ferromagnetic (AFM) to transient ferromagnetic (FM). The microscopic physics of this ultra-fast spin modulation is dominated by charge flows created by spin-preserving optical excitations, one of the fastest means of manipulating an electronic system by light. We demonstrate this mechanism to be universally applicable to AFM, FM, multilayers and bulk systems, and provide three rules that encapsulate the laser induced early time magnetization dynamics of multi-sub-lattice systems.