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Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralowmagnetic damping are relevant for magnon-based spintronics and low-powerwave-like computing. The excitation frequency of spin waves in YIG is ratherlow in weak external magnetic fields because of its small saturationmagnetization, which limits the potential of YIG films for high-frequencyapplications. Here, we demonstrate how exchange-coupling to a CoFeB filmenables efficient excitation of high-frequency perpendicular standing spinwaves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniformmicrowave magnetic fields. In the 295-nm-thick YIG film, we measure intensePSSW modes up to 10th order. Strong hybridization between the PSSW modes andthe ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossingbehavior in broadband spin-wave spectra. A dynamic exchange torque at theYIG/CoFeB interface explains the excitation of PSSWs. The localized torqueoriginates from exchange coupling between two dissimilar magnetizationprecessions in the YIG and CoFeB layers. As a consequence, spin waves areemitted from the YIG/CoFeB interface and PSSWs form when their wave vectormatches the perpendicular confinement condition. PSSWs are not excited when theexchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.Micromagnetic simulations confirm the exchange-torque mechanism.

Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films