  Magnetic bit writing by short-wave magnons without conversion to the
electrical domain is expected to be a game-changer for in-memory computing
architectures. Recently, the reversal of nanomagnets by propagating magnons was
demonstrated. However, experiments have not yet explored different wavelengths
and the nonlinear excitation regime of magnons required for computational
tasks. We report on the magnetization reversal of individual 20-nm-thick
Ni81Fe19 (Py) nanostripes integrated onto 113-nm-thick yttrium iron garnet
(YIG). We suppress direct interlayer exchange coupling by an intermediate layer
such as Cu and SiO2. Exciting magnons in YIG with wavelengths {\lambda} down to
148 nm we observe the reversal of the integrated ferromagnets in a small
opposing field of 14 mT. Magnons with a small wavelength of {\lambda} = 195 nm,
i.e., twice the width of the Py nanostripes, induced the reversal at an
unprecedentedly small spin precessional power of about 1 nW after propagating
over 15 {\mu}m in YIG. Considerations based on dynamic dipolar coupling explain
the observed wavelength dependence of magnon-induced reversal efficiency. For
an increased power the stripes reversed in an opposing field of only about 1
mT. Our findings are important for the practical implementation of nonvolatile
storage of broadband magnon signals in YIG by means of bistable nanomagnets
without the need of an appreciable global magnetic field.
