  Spin waves, the collective excitations of the magnetic order parameter, and
magnons, the associated quasiparticles, are envisioned as possible data
carriers in future wave-based computing architectures. On the road towards
spin-wave computing, the development of a diode-like device capable of
transmitting spin waves in only one direction, thus allowing controlled signal
routing, is an essential step. Here, we report on the design and experimental
realization of a microstructured magnonic diode in a ferromagnetic bilayer
system. Effective unidirectional propagation of spin waves is achieved by
taking advantage of nonreciprocities produced by dynamic dipolar interactions
in transversally magnetized media, which lack symmetry about their horizontal
midplane. More specifically, dipolar-induced nonreciprocities are used to
engineer the spin-wave dispersion relation of the bilayer system so that the
group velocity is reduced to very low values for one direction of propagation,
and not for the other, thus producing unidirectional slow spin waves. Brillouin
light scattering and propagating spin-wave spectroscopy are used to demonstrate
the diode-like behavior of the device, the composition of which was previously
optimized through micromagnetic simulations. simulations.
