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Creators/Authors contains: "Varela-Manjarres, Jalil"

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  1. Abstract

    One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, thez-axis) with frequencyω0due to absorption of low-power microwaves of frequencyω0under the resonance conditions and in the absence of any applied bias voltage. The two-decades-old ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that componentISzof spin current vector(ISx(t),ISy(t),ISz)ω0is time-independent whileISx(t)andISy(t)oscillate harmonically in time with a single frequencyω0whereas pumped charge current is zeroI0in the same adiabaticω0limit. Here we employ more general approaches than the ‘standard model’, namely the time-dependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin–orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spinISα(t)and chargeI(t) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiplesNω0of the driving frequencyω0. The cutoff order of such high harmonics increases with SOC strength, reachingNmax11in the one-dimensional FM or AFM models chosen for demonstration. A higher cutoffNmax25can be achieved in realistic two-dimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures.

     
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