Direct evidence of superdiffusive terahertz spin current arising from ultrafast demagnetization process

Abstract

Using element-specific measurements of the ultrafast demagnetization of Ru/Fe65Co35 heterostructures, we show that Ru can exhibit a significant magnetic contrast (5% asymmetry) resulting from ultrafast spin currents emanating from the demagnetization process of the FeCo layer. We use this magnetic contrast to investigate how superdiffusive spin currents are affected by the doping of heavy elements in the FeCo layer. We find that the spin currents are strongly suppressed by Re doping, in accordance with the theoretically predicted terahertz spin current in Ru, utilizing the superdiffusive spin transport model.

Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics with example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn

“…While pumped (term used to signify current generation in the absence of any bias voltage [18][19][20][21]) spin currents from laser-driven magnetic layers, with short attenuation length ∼ 10 nm [22], have been observed experimentally [22,23], microscopic mechanisms behind them and their relation, or even necessity [10], to demagnetization remain heavily debated [10,24]. For example, optically excited hot electrons [10] become spinpolarized by magnetic layer to comprise spin current in the so-called "superdiffusive mechanism" [10,[25][26][27], whose flowing out of the FM layer then contributes to demagnetization. Conversely, the cause and effect are reversed in the so-called "dM/dt mechanism" [24,28,29] FIG.…”