  We theoretically demonstrate linear spin-wave nonreciprocity in a Ni80Fe20
nanostripe waveguide, based on interband magnonic transitions induced by a
time-reversal and spatialinversion symmetry breaking magnetic field. An
analytical coupled-mode theory of spin waves, developed to describe the
transitions which are accompanied by simultaneous frequency and wavevector
shifts of the coupled spin waves, is well corroborated by numerical
simulations. Our findings could pave the way for the realization of spin-wave
isolation and the dynamic control of spin-wave propagation in nanoscale
magnonic integrated circuits via an applied magnetic field.
