Floquet control of indirect exchange interaction in periodically-driven magnetic lateral heterostructures

Controlling the indirect exchange interaction between ferromagnetic impurities is pivotal for spintronic information transfer and storage. We present a theory for the RKKY interaction in a monochromatically irradiated magnetic lateral heterostructure (MLH). The MLH is composed of a left-side ferromagnet, a two-dimensional electron gas, and a right-side ferromagnet. Using the Keldysh-Floquet formalism, we calculate the time-averaged spin susceptibility and RKKY interaction mediated by the irradiated MLHs. Our results show that the emergence of non-equilibrium Floquet states under periodic driving leads to two qualitatively different RKKY regimes: 1) when the n ≤ 0 Floquet bands intersect the Fermi level, the sign and period of oscillation of the RKKY interaction are controllable by the frequency and amplitude of the laser; 2) when the n ≤ -1 Floquet bands intersect the Fermi level, the RKKY coupling does not display oscillations and remains ferromagnetic, resembling the exchange interaction mediated by insulating spacers. Our work demonstrates the feasibility of optically controlling the indirect exchange interaction with coherent laser fields.