Journal
PHYSICAL REVIEW B
Volume 105, Issue 18, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.105.184408
Keywords
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Funding
- German Research Foundation [328545488, 358671374]
- European Union [681917]
- Spanish Ministry of Science and Innovation [PID2020-112914RB-I00]
- National Natural Science Foundation of China [61988102, 61975110]
- Czech Science Foundation [21-28876J]
- Spanish MECD [FPU014/02546, EST17/00382]
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Spin transport is crucial for future spintronic devices. Laser-driven spin currents in F|Pt stacks are studied to identify the mechanism of spin transport, which is mediated by spin-polarized conduction electrons and/or torque between electron spins. The study reveals similar dynamics and provides an estimation of the spin-mixing conductance of the interfaces. In addition, two spin-current components with opposite directions are observed in the half-metallic ferrimagnet Fe3O4, supporting the magneto-electronic model of Fe3O4.
Spin transport is crucial for future spintronic devices operating at bandwidths up to the terahertz range. In F|N thin-film stacks made of a ferromagnetic/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 crossover 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 yttrium iron garnet, gadolinium iron garnet (GIG) and ?? -Fe2O3, identical dynamics is observed. It arises from the terahertz interfacial spin Seebeck effect (SSE), is fully determined by the relaxation of the electrons in the metal layer, and provides a rough estimate of the spin-mixing conductance of the GIG/Pt and ?? -Fe2O3/Pt interfaces. 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 pyrospintronic effect and can consistently be assigned to ultrafast demagnetization of minority-spin hopping electrons. This observation supports the magneto-electronic model of Fe3O4. In general, our results provide a route to the contact-free separation of torque- and conduction-electron-mediated spin currents.
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