Microwave control of thermal-magnon spin transport

Abstract

We observe that an rf microwave field strongly influences the transport of incoherent thermal magnons in yttrium iron garnet. Ferromagnetic resonance in the nonlinear regime suppresses thermal magnon transport by 95%. The transport is also modulated at non-resonant conditions in two cases, both related to the magnon band minimum. Firstly, a strong enhancement of the nonlocal signal appears at a static magnetic field below the resonance condition. This increase only occurs at one field polarity and can be as large as 800%. We attribute this effect to magnon kinetic processes, which give rise to band-minimum magnons and high-energy chiral surface modes. Secondly, the signal increases at a static field above the resonance condition, where the rf frequency coincides with the magnon band minimum. Our study gives insight into the interplay between coherent and incoherent spin dynamics: The rf field modifies the occupation of relevant magnon states and, via kinetic processes, the magnon spin transport. arXiv:1810.11667v1 [cond-mat.mes-hall]

Spin Transport in a Magnetic Insulator with Zero Effective Damping

“…As the damping compensation may also lead to coherent magnetization dynamics, this warrants the question how a coherent magnetization state created by ferromagnetic resonance (FMR) affects the transport properties. In stark contrast to the reduction of the magnon resistance due to the damping compensation, we find an increase of the magnon resistance when coherently driving the YIG magnetization by a microwave magnetic field [25] [30]. This demonstrates that the effective compensation of magnetic damping is responsible for the formation of the ultra-low magnon resistance state -and not the coherence of the magnetization precession.…”

All‐Electrical Magnon Transport Experiments in Magnetically Ordered Insulators

“…After the first theoretical prediction and experimental demonstration of all-electrical magnon transport in NM/MOI heterostructures, [61][62][63] experiments in this regard were conducted not only in ferri-MOIs [23,[64][65][66][67][68][69][70][72][73][74][75][76]181,223,224] but also in AFIs. [71,[77][78][79][80]171] In this way, we obtained access to studying magnon transport, corresponding to GHz or even THz frequencies, utilizing magnetotransport techniques and DC charge currents.…”

“…Several groups have already made tremendous contributions toward a better understanding of all-electrical magnon transport experiments in MOIs. [64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] These experiments utilize a heterostructure consisting of two NM strips in contact with the MOI, as shown in Figure 2. In the experiment, a charge current density j q is applied to the NM injector strip, which generates a spin current density j s .…”

Efficient Gating of Magnons by Proximity Superconductors

“…In the limit that The chiral damping theory above holds for coherent spin waves with well defined momentum as excited by narrow striplines, and we may expect similar but smaller effects in the diffuse regime of magnon transport. An asymmetry in the propagation of carriers into opposite directions has been reported in the transport of incoherent magnons in YIG films under microwave [32] or spin Hall effect [33,34] excitation. References [33,34] appear to support our results without having to resort to spinorbit interactions.…”