Magnon-magnon coupling in synthetic ferrimagnets
A. Sud, Kei Yamamoto, Kazuya Suzuki, Shigemi Mizukami, H. Kurebayashi
Abstract
Magnetic multilayers with interlayer exchange coupling have been widely studied for both static and dynamic regimes. Their dynamical responses depend on the exchange coupling strength and magnetic properties of individual layers. Magnetic resonance spectra in such systems are conveniently discussed in terms of coupling of acoustic and optical modes. At a certain value of applied magnetic field, the two modes come close to being degenerate and the spectral gap indicates the strength of mode hybridization. In this work, we theoretically and experimentally study the mode hybridization of interlayer-exchange-coupled moments with dissimilar magnetization and thickness of two ferromagnetic layers. In agreement with symmetry analysis for eigenmodes, our low-symmetry multilayers exhibit sizable spectral gaps for all experimental conditions. The spectra agree well with the predictions from the Landau-Lifshitz-Gilbert equation at the macrospin limit whose parameters are independently fixed by static measurements.