  We theoretically investigate the collective excitation of multiple
(sub)millimeter-sized ferromagnets mediated by waveguide photons. By the
position of the magnets in the waveguide, the magnon-photon coupling can be
tuned to be chiral, i.e., magnons only couple with photons propagating in one
direction, leading to asymmetric transfer of angular momentum and energy
between the magnets. A large imbalance in the magnon number distribution over
the magnets can be achieved with a long chain of magnets, which concentrate at
one edge. The chain also supports standing waves with low radiation efficiency
that is inert to the chirality.
