Giant nonreciprocity of surface acoustic waves enabled by the magnetoelastic interaction

Abstract

Nonreciprocity, the defining characteristic of isolators, circulators, and a wealth of other applications in radio/microwave communications technologies, is generally difficult to achieve as most physical systems incorporate symmetries that prevent the effect. In particular, acoustic waves are an important medium for information transport, but they are inherently symmetric in time. In this work, we report giant nonreciprocity in the transmission of surface acoustic waves (SAWs) on lithium niobate substrate coated with ferromagnet/insulator/ferromagnet (FeGaB/Al2O3/FeGaB) multilayer structure. We exploit this structure with a unique asymmetric band diagram and expand on magnetoelastic coupling theory to show how the magnetic bands couple with acoustic waves only in a single direction. We measure 48.4-dB (power ratio of 1:69,200) isolation that outperforms current state-of-the-art microwave isolator devices in a previously unidentified acoustic wave system that facilitates unprecedented size, weight, and power reduction. In addition, these results offer a promising platform to study nonreciprocal SAW devices.

Phase Nonreciprocity of Microwave‐Frequency Surface Acoustic Waves in Hybrid Heterostructures with Magnetoelastic Coupling

“…[4][5][6] Although nonreciprocity of magnetoelastic waves (e.g., hybridized SAW-SW) have been studied for a long time, [7,8] it is only recently the practically usable levels (giant and/or ultra-wideband) of nonreciprocity of SAW propagation losses have been achieved. [9][10][11][12][13][14] These novel results open a way for the development of efficient microwave SAW isolators, compatible with the modern SAW technology.Isolators, however, are not the only nonreciprocal devices, that are necessary for the further development of microwavefrequency SAW-based signal processing technology. Circulators and nonreciprocal phase shifters are also needed.Although there exists a method to build a circulator using several isolators, [15,16] this method is hardly compatible with the existing SAW technology.…”

“…[4][5][6] Although nonreciprocity of magnetoelastic waves (e.g., hybridized SAW-SW) have been studied for a long time, [7,8] it is only recently the practically usable levels (giant and/or ultra-wideband) of nonreciprocity of SAW propagation losses have been achieved. [9][10][11][12][13][14] These novel results open a way for the development of efficient microwave SAW isolators, compatible with the modern SAW technology.…”

“…Naturally, if an SW is, itself, nonreciprocal, ω k ≠ ω −k , the spectral gaps are formed at different frequency and wave number positions, and the coupled waves demonstrate higher nonreciprocity. [9,13] It may seem intuitively that working within the spectral gaps is the best way to achieve large phase nonreciprocity of acoustic waves, as the wave dispersion relation is most strongly modified in these regions. It turns out, however, that working in the gaps is practically impossible.…”

“…[10], and a giant nonreciprocity of SAW losses in a similar SAFM structure has been practically realized in ref. [13].…”

“…This gap in SAFM can be created by an in-plane anisotropy, which can be either the crystalline anisotropy of the magnetic material, like in ref. [13], or the shape anisotropy of the SAFM sample, for example, if the SAFM is patterned in the form an array of elongated stripes. As it is common for the magnetoelastic coupling of SAW, [19,26] the angle φ between the anisotropy axis e e an (and, consequently, the static magnetization M M i ) www.advelectronicmat.de and the wave propagation direction should not be close to φ = 0 or φ = π/2 in order to achieve efficient coupling between the SAW and SW.…”