  The inevitable Gilbert damping in magnetization dynamics is usually regarded
as detrimental to spin transport. Here we apply a general feature of chiral
non-Hermitian dynamics to a ferromagnetic-insulator--normal-metal
heterostructure to show that the strong momentum dependence and chirality of
the eddy-current-induced damping also causes beneficial scattering properties:
A potential barrier that reflects magnon wave packets becomes unidirectionally
transparent in the presence of a metallic cap layer. Passive magnon gates that
turn presumably harmful dissipation into useful functionalities should be
useful for future quantum magnonic devices.
