Nonreciprocal Transmission of Incoherent Magnons with Asymmetric Diffusion Length

Unequal transmissions of spin waves along opposite directions provide useful functions for signal processing. So far, the realization of such nonreciprocal spin waves has been mostly limited at a gigahertz frequency in the coherent regime via microwave excitation. Here we show that, in a magnetic bilayer stack with chiral coupling, tunable nonreciprocal propagation can be realized in spin Hall effect-excited incoherent magnons, whose frequencies cover the spectrum from a few gigahertz up to terahertz. The sign of nonreciprocity is controlled by the magnetic orientations of the bilayer in a nonvolatile manner. The nonreciprocity is further verified by measurements of the magnon diffusion length, which is unequal along opposite transmission directions. Our findings enrich the knowledge on magnetic relaxation and diffusive transport and can lead to the design of a passive directional signal isolation device in the diffusive regime.

Automated summary

The study shows that tunable nonreciprocal propagation can be achieved in incoherent magnons excited by the spin Hall effect in a magnetic bilayer stack with chiral coupling. This finding enriches the understanding of magnetic relaxation and diffusive transport, and has the potential to lead to the design of passive directional signal isolation devices in the diffusive regime.