The ability to control and tune magnetic dissipation is a key concept of emergent spintronic technologies. Magnon scattering processes constitute a major dissipation channel in nanomagnets, redefine their response to spin torque, and hold the promise for manipulating magnetic states on the quantum level. Controlling these processes in nanomagnets, while being imperative for spintronic applications, has remained difficult to achieve. Here, we propose an approach for controlling magnon scattering by a switch that generates nonuniform magnetic field at nanoscale. We provide an experimental demonstration in magnetic tunnel junction nanodevices, consisting of a free layer and a synthetic antiferromagnet. By triggering the spin-flop transition in the synthetic antiferromagnet and utilizing its stray field, magnon interaction in the free layer is toggled. The results open up avenues for tuning nonlinearities in magnetic neuromorphic applications and for engineering coherent magnon coupling in hybrid quantum information technologies.

Nanomagnets are the building blocks of many existing and emergent spintronic technologies. Magnetization dynamics of nanomagnets is often dominated by nonlinear processes, which have been recently shown to have many surprising features and far-reaching implications for applications. Here we develop a theoretical framework uncovering the selection rules for multimagnon processes and discuss their underlying mechanisms. For its technological relevance, we focus on the degenerate three-magnon process in thin elliptical nanodisks to illustrate our findings. We parameterize the selection rules through a set of magnon interaction coefficients which we calculate using micromagnetic simulations. We postulate the selection rules and investigate how they are altered by perturbations, that break the symmetry of static magnetization configuration and spatial spin-wave profiles and that can be realized by applying off-symmetry-axis or nonuniform magnetic fields. Our work provides the phenomenological understanding into the mechanics of magnon interaction as well as the formalism for determining the interaction coefficients from simulations and experimental data. Our results serve as a guide to analyze magnon processes inherently present in spin-torque devices for boosting their performance or to engineer a specific nonlinear response of a nanomagnet used in neuromorphic or quantum magnonic application.