Large Nonreciprocal Propagation of Surface Acoustic Waves in Epitaxial Ferromagnetic/Semiconductor Hybrid Structures

Abstract

Non-reciprocal propagation of sound, that is, the different transmission of acoustic waves traveling along opposite directions, is a challenging requirement for the realization of devices like acoustic diodes and circulators. Here, we demonstrate the efficient non-reciprocal transmission of surface acoustic waves (SAWs) propagating along opposite directions of a GaAs substrate coated with an epitaxial Fe 3 Si film. The non-reciprocity arises from the acoustic attenuation induced by the magneto-elastic (ME) interaction between the SAW strain field and spin waves in the ferromagnetic film, which depends on the relative angle between SAW propagation direction and magnetization.The acoustic transmission non-reciprocity, defined as the difference between the transmitted acoustic power for forward and backward propagation under ME resonance, reaches record values of up to 20%. The experimental results are well accounted for by a model for ME interaction, which also shows that non-reciprocity can be further enhanced by optimization of the sample design. These results make Fe 3 Si/GaAs a promising platform for the realization of efficient non-reciprocal SAW devices.

Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling

“…Our findings go beyond as we theoretically consider the magnetorotation coupling and thereby explain the experimental value of 100% at optimized experimental conditions. This intriguing result is in contrast to ( 11 ) where it was speculated that the nonreciprocal attenuation depended critically on the magnetic damping.…”

“…Therefore, we extend the previous model taking into account the magneto-rotation coupling, which turns out to be crucial for the giant NR in the present work. The rectification effect that we observe is far larger than the record values of 20% recently reported in ( 11 ). Our findings go beyond as we theoretically consider the magnetorotation coupling and thereby explain the experimental value of 100% at optimized experimental conditions.…”

“…Our findings go beyond as we theoretically consider the magnetorotation coupling and thereby explain the experimental value of 100% at optimized experimental conditions. This intriguing result is in contrast to (11) where it was speculated that the nonreciprocal attenuation depended critically on the magnetic damping. Figure 2A shows the schematics of SAW propagation through a heterostructure, which consists of four layers, Ta(10 nm)/Co 20 Fe 60 B 20 (1.6 nm)/ MgO(2 nm)/Al 2 O 3 (10 nm), on a piezoelectric substrate, Y-cut LiNbO 3 .…”

“…Consequently, the a-FMR generates a spin current that can be converted to charge current by the inverse Edelstein effect (8) or spin Hall effect (9). Evidence of nonreciprocal behaviors in attenuation of amplitudes was reported when SAWs interacted with magnetic films (8,10,11). In these works, the origin of the nonreciprocal behaviors was attributed to magnetoelastic coupling that induced attenuation, and the interference between the longitudinal and shear components of the strain tensor in SAWs.…”

Nonreciprocal surface magnetoelastic dynamics

“…The model device we consider is one to many magnetic nanowires on top of a high-quality acoustic insulator rather than the extended magnetic film. We employ nanowire with thickness much smaller than the wavelength of the SAWs, in which situation the effect from the shear strain on the upper and lower surface cancels, different from that of thick films [19,68]. Therefore, in the wire setup the nonreciprocity comes from the edge effect that is sensitive to the wire width and is strong when the wire width is comparable to the SAW wavelength.…”