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technical paper
Reversal of nanostructured ferromagnets by magnon pulses in underlying yttrium iron garnet
Magnon-induced switching of nanomagnets is one of the key milestones to realize magnon-based in-memory computing. Spin waves (magnons) have been reported to move domain walls 1 and induce the reversal of Ni81Fe19
(Py) nanostripes (NSs) fabricated on YIG 2. We report the observation of magnon-induced reversal of bistable nanomagnets
by time-resolved Brillouin light scattering microscopy. We used Py nanostripes separated from YIG via an intermediate insulating layer (Fig. 1). Thereby, we suppressed the interlayer
exchange interaction between Py and YIG. A coplanar waveguide (CPW) was fabricated on top of an array of Py NSs. The device performed as a grating coupler 3. Short-wave magnons
were emitted into YIG which then propagated underneath remotely positioned nanostripes. We saturated the device at +80 mT and then decreased the field to -24 mT. We measured the
thermal magnon spectrum of the unswitched Py NSs before magnon emission. After magnon excitation we observed characteristic modifications in the magnon spectrum (Fig. 2). Beyond a
critical power level, peak A and peak B vanished and a new peak B’ appeared. These specific modifications indicated the reversal of the nanomagnets and occurred for both the pulsed and
continuous wave magnon excitation. Our experimental data suggest that dipolar coupling is sufficient to achieve magnon-induced switching. We report experiments performed in the linear
and non-linear regime of magnon excitation. The latter experiments are important for the realization of recurrent neural networks based on ferromagnet/ferrimagnet hybrid structures as
proposed in Ref. 4. Our results suggest that the storage of magnon signals in reversed magnetic bits become possible thus paving the way towards magnon-based in-memory computing
platforms. We acknowledge the financial support from SNSF via Grant No. 197360.
References
1 J. Han, P. Zhang, J.T. Hou, Science, Vol. 366, 1121-1125 (2019)
2 K. Baumgaertl, D. Grundler, submitted
3 H. Yu, G. Duerr, R. Huber, Nature Communications, Vol. 4, 2702 (2013)
4 Á. Papp, W. Porod, G. Csaba, Nature Communications, Vol. 12, 6422 (2021)
Sketch of the device. An oscillating current is injected in the CPW to excite magnons which propagate in the bare YIG until reaching separately positioned Py nanostripes. Each material
thickness is indicated between parenthesis.
BLS thermal magnon spectra on Py stripes before (magenta) and after (black) magnon excitation at -24 mT.