Observation of Acousto-Plasmo-Magnonic Frequency Combs in Artificial 2D Magnonic Crystals

The coupling between spin waves and hybridized phonon-plasmon waves in a 2D periodic array of magnetostrictive nanomagnets (an artificial 2D magnonic crystal) delineated on a thin film of aluminum deposited on a silicon substrate is studied with time resolved magneto-optical Kerr effect (TR-MOKE) spectroscopy. The surface plasmons originating from the aluminum layer couple with phonons generated in the silicon substrate when exposed to ultrashort laser pulses, and the resulting hybridized phonon-plasmon mode then couples strongly with magnon modes in the nanomagnets to produce an acousto-plasmo-spin wave "frequency comb" in the magnonic crystal that spans two octaves. We also observe giant parametric amplification of spin wave modes (power amplification of 200X) in this system caused by the transfer of energy from the hybridized phonon-plasmon modes to the spin wave modes. Both the frequency comb and the parametric amplification can have many applications in precision measurements and coherent plasmon driven spintronics.