Gap solitons in magnonic crystals with loads

Abstract

Magnonics, using spin waves for information transfer, offers a promising alternative to CMOS limitations. While nonlinear spin wave phenomena like solitons were studied in non-periodic ferrite structures, gap soliton research in periodic systems was limited to thick YIG films (10-15 μm).
This work studies nonlinear spin wave propagation in a 100-nm YIG-based magnonic crystal with surface-etched periodic grooves. Using the coupled-wave method accounting for wave reflections, the model elucidates gap soliton formation via trapping of bandgap-frequency spin waves at increased input amplitudes.
Numerical simulations reveal gap soliton formation at bandgap frequencies above an amplitude threshold, with the soliton exhibiting higher amplitude and shorter duration than the input pulse. This soliton propagates slower than the linear group velocity in the magnonic crystal.
Increasing input pulse duration lowers the gap soliton amplitude threshold and can enable multiple soliton generation. This threshold critically depends on the periodic medium's parameters: it requires an optimal coupling coefficient range (insufficient or excessive coupling inhibits formation) and decreases with higher nonlinearity coefficients or greater frequency detuning from the bandgap center.
Spin current in interfaced normal metal layers critically affects the gap soliton formation threshold: positive polarity reduces it by amplifying spin waves, while negative polarity increases it via attenuation.
In semiconductor-loaded magnonic crystals, electric current renders wave equation coefficients complex, making soliton formation threshold dependent on semiconductor conductivity and carrier drift velocity, occurring within specific current ranges.
These findings highlight nanoscale periodic ferromagnets as promising for frequency-selective devices utilizing gap solitons.

Speaker

Ochkina Varvara
Saratov State University
Russia

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