Magneto-Elastic Coupling between Surface Acoustic & Surface Spin Waves

Non-reciprocal propagation of surface acoustic waves (SAW) can be induced by using their coupling with surface spin waves (SSW). Here, this problem is studied theoretically for SAW and SSW in YIG/GGG bilayers. Expression for the SAW-SSW coupling rate is obtained using Kalinikos-Slavin theory of dipole-exchange SSW [1]. The maximum coupling exceeding 40 MHz is achieved for magnetic field applied at 45⁰ to the direction of wave propagation and SAW frequency ~ 2 GHz. For YIG thicknesses below 200 nm, the SSW profile remains symmetric and the SAW-SSW coupling is reciprocal. With the increase of YIG thickness, the nonreciprocity of magnetoelastic coupling gradually increases; however, for YIG thickness above 1.3 µm, the SAW-SSW gap becomes wider than the gap between SSW and higher-order standing spin waves, which substantially complicates the spectrum of the hybrid magneto-acoustic waves. The induced SAW non-reciprocity is most clearly observed for YIG films with intermediate thicknesses of 300 nm – 1.2 µm. In this range, the SAW/SSW coupling rates for oppositely propagating waves may differ by a factor of 2.5 which allows one to use this phenomenon for a number of practical applications.



References

[1] B A Kalinikos & A N Slavin 1986 J. Phys. C: Solid State Phys. 19 7013