Strong coupling of quantized spin waves in ferromagnetic bilayers

We formulate a strong-coupling theory for perpendicular standing spin waves (PSSWs) in ferromagnetic bilayers with the interlayer exchange coupling (IEC). Employing the Hoffmann boundary condition and the energy-flow continuity across the interface, we show that the PSSWs are still quantized but with nonintegral quantum numbers, similar to the case with a surface pinning but in sharp contrast to that with a free surface. The magnon-magnon coupling is characterized by the spectrum splitting which is linear with the IEC in the weak-coupling region but getting saturated in the strong-coupling limit. Analytical predictions are verified by full micromagnetic simulations with good agreement.

Automated summary

In this study, a strong-coupling theory for perpendicular standing spin waves (PSSWs) in ferromagnetic bilayers with interlayer exchange coupling (IEC) is formulated. PSSWs are shown to be quantized with nonintegral quantum numbers, and the magnon-magnon coupling is characterized by spectrum splitting linearly with the IEC which gets saturated in the strong-coupling limit. Analytical predictions are confirmed by full micromagnetic simulations with good agreement.