Probing optical spin-currents using THz spin-waves in noncollinear magnetic bilayers

Abstract

Optically induced spin currents have proven to be useful in spintronics applications, allowing for sub-ps all-optical control of magnetization. However, the mechanism responsible for their generation is still heavily debated. Here we use the excitation of spin-current induced THz spin-waves in noncollinear bilayer structures to directly study optical spin-currents in the time domain. We measure a significant laser-fluence dependence of the spin-wave phase, which can quantitatively be explained assuming the spin current is proportional to the time derivative of the magnetization. Measurements of the absolute spin-wave phase, supported by theoretical calculations and micromagnetic simulations, suggest that a simple ballistic transport picture is sufficient to properly explain spin transport in our experiments and that the damping-like optical STT dominates THz spin-wave generation. Our findings suggest laser-induced demagnetization and spin-current generation share the same microscopic origin.

arXiv commentSupplementary information included

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• Ultrafast demagnetization in ferromagnetic materials: Origins and progress
• Origins of electromagnetic radiation from spintronic terahertz emitters: A time-dependent density functional theory plus Jefimenko equations approach
• Element resolved evidence of superdiffusive terahertz spin current arising from ultrafast demagnetization process
• Charge and spin current pumping by ultrafast demagnetization dynamics
• Ultrafast magnetization reversal in ferromagnetic spin-valves: an s-d model perspective
• Deciphering the origin of spin current in spintronic terahertz emitters and its imprint on their electromagnetic radiation via time-dependent density functional theory
• Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics: Example of ultrafast-light-driven Weyl antiferromagnet Mn${}_3$Sn
• Spin-polarized hot electron transport versus spin pumping mediated by local heating
• Different spin relaxation property observed in linearly and circularly polarized laser induced terahertz emission from Bi/Co bilayer
• Exploring terahertz-scale exchange resonances in synthetic ferrimagnets with ultrashort optically induced spin currents
• Probing Laser-Induced Spin-Current Generation in Synthetic Ferrimagnets Using Spin Waves
• Optimizing spin-based terahertz emission from magnetic heterostructures