Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport

Abstract

Spin transport is crucial for future spintronic devices operating at bandwidths up to the terahertz (THz) range. In F|N thin-film stacks made of a ferro/ferrimagnetic layer F and a normal-metal layer N, spin transport is mediated by (1) spin-polarized conduction electrons and/or (2) torque between electron spins. To identify a cross-over from (1) to (2), we study laser-driven spin currents in F|Pt stacks where F consists of model materials with different degrees of electrical conductivity. For the magnetic insulators YIG, GIG and maghemite, identical dynamics is observed. It arises from the THz interfacial spin Seebeck effect (SSE), is fully determined by the relaxation of the electrons in the metal layer and provides an estimate of the spin-mixing conductance of the GIG/Pt interface. Remarkably, in the half-metallic ferrimagnet Fe3O4 (magnetite), our measurements reveal two spin-current components with opposite direction. The slower, positive component exhibits SSE dynamics and is assigned to torque-type magnon excitation of the A- and B-spin sublattices of Fe3O4. The faster, negative component arises from the pyro-spintronic effect and can consistently be assigned to ultrafast demagnetization of e-sublattice minority-spin hopping electrons. This observation supports the magneto-electronic model of Fe3O4. In general, our results provide a new route to the contact-free separation of torque- and conduction-electron-mediated spin currents.

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Cited by in corpus (8)

• Spintronic Sources of Ultrashort Terahertz Electromagnetic Pulses
• Spintronic THz emitters based on transition metals and semi-metals/Pt multilayers
• Accessing ultrafast spin-transport dynamics in copper using broadband terahertz spectroscopy
• Ultrafast magnetization reversal in ferromagnetic spin-valves: an s-d model perspective
• 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
• Finite-frequency spin conductance of a ferro-/ferrimagnetic-insulator|normal-metal interface
• Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures
• Probing Laser-Induced Spin-Current Generation in Synthetic Ferrimagnets Using Spin Waves