Element-selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets

Stoner and Heisenberg excitations in magnetic materials are inherently\ndifferent. The former involves an effective reduction of the exchange\nsplitting, whereas the latter comprises excitation of spin-waves. In this work,\nwe test the impact of these two excitations in the hybrid Stoner-Heisenberg\nsystem FePd. We present a microscopic picture of ultrafast demagnetization\ndynamics in this alloy, which represents both components of strong local\nexchange splitting in Fe, and induced polarization in Pd. We identify\nspin-orbit coupling and optical inter-site spin transfer as the two dominant\nfactors for demagnetization at ultrashort timescales. By tuning the external\nlaser pulse, the extrinsic inter-site spin transfer can be manipulated for site\nselective demagnetization on femtosecond time scales providing the fastest way\nfor optical and selective control of the magnetization dynamics in alloys.\nRemarkably, the drastic difference in origin of the magnetic moment of the Fe\nand Pd species is not deciding the initial magnetization dynamics in this\nalloy.\n