Tuning magnonic devices with on-chip permanent micromagnets

One of the most appealing features of magnonics is the easy tunability of spin-wave propagation via external magnetic fields. Typically, this requires bulky and power-hungry electromagnets, which are not compatible with device miniaturization. Here, we propose a different approach, exploiting the stray field from permanent micromagnets integrated on the same chip of a magnonic waveguide. In our monolithic device, we employ two SmCo square micromagnets (10 x 10 mu m2) flanking a CoFeB conduit at different distances from its axis, which produces a tunable transverse bias field between 7.5 and 3.0 mT in the conduit region between the magnets. This field is large enough to significantly affect the spin-wave propagation, when an external transverse bias field of 60 mT is applied to stabilize the Damon-Eshbach configuration. Spin waves excited by an antenna just outside the region between the magnets, indeed, enter a region with a variable higher (or lower) effective field depending on the parallel (or antiparallel) alignment between the external and micromagnets fields. Consequently, the attenuation length and phase shift of Damon-Eshbach spin waves can be tuned in a wide range by changing the parallel-antiparallel configuration of the external bias and the distance between SmCo micromagnets and the CoFeB conduit. This work demonstrates the potential of permanent micromagnets for the realization of low-power, integrated magnonic devices with tunable functionalities.