Enhancement of spin current generation by magnon-phonon coupling using acoustic cavity

ontext of project
Recently, we demonstrated the spin current generation via magnon – phonon coupling, reaching a maximum spin current JS on the order of 10^8 A/m^2 [Physical Review B 97 (18), 180301(R) (2018)]. This encouraging value is three orders of magnitude smaller than JS,DW ~ 10^11 A/m^2 required for current-induced motion of domain walls (DWs) or spin torques, but already two orders of magnitude beyond the threshold current needed for the motion of Bloch-type Skyrmions in chiral magnets. Enhancement of magnon – phonon would deliver improvements in the generation of spin current of at least four times by minimizing energy losses by acoustic wave reflectors. When forming an optimized acoustic cavity, the improvement of spin current generation no longer depends only in the energy losses but the enhancement of the magnon – phonon coupling strength.
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Abstract of our recent work
Surface acoustic waves (SAWs) in the GHz frequency range can inject spin currents dynamically into adjacent non-magnetic layers via the spin pumping effect associated with ferromagnetic resonance. Here, we demonstrate an enhancement of acoustic ferromagnetic resonance and spin current generation by a pair of SAW reflector gratings, which form an acoustic analog of the distributed Bragg reflector cavity. In the experiment, we confirmed 2.04±0.02 times larger SAW power absorption in a device with cavity than in the case of no acoustic cavity. We confirmed up to 2.96±0.02 times larger spin current generation by measuring electric voltages generated by the inverse Edelstein effect at the interface between Cu and Bi2O3. The results suggest that acoustic cavities would be useful to enhance the conversion efficiency in SAW driven coupled magnon–phonon dynamics. 

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Enhancement of acoustic spin pumping by acoustic distributed Bragg reflector cavity
Y. Hwang, J. Puebla, M. Xu, A. Lagarrigue, K. Kondou and Y. Otani
Appl. Phys. Lett. 116, 252404 (2020), Editor's pick
aip.scitation.org/doi/10.1063/5.0011799