It is desirable to experimentally demonstrate an extremely high resonant frequency, assisted by strain-spin coupling, in technologically important perpendicular magnetic materials for device applications. Here, we directly observe the coupling of magnons and phonons in both time and frequency domains upon femtosecond laser excitation. This strain-spin coupling leads to a magnetoacoustic resonance in perpendicular magnetic [Co/Pd]n multilayers, reaching frequencies in the extremely high frequency (EHF) band, e.g., 60 GHz. We propose a theoretical model to explain the physical mechanism underlying the strain-spin interaction. Our model explains the amplitude increase of the magnetoacoustic resonance state with time and quantitatively predicts the composition of the combined strain-spin state near the resonance. We also detail its precise dependence on the magnetostriction. The results of this work offer a potential pathway to manipulating both the magnitude and timing of EHF and strongly coupled magnon-phonon excitations.
Bibliographical noteFunding Information:
We thank P. Crowell from University of Minnesota for valuable discussions and suggestions. Funding: This work was partially supported by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, and by ASCENT, one of six centres in JUMP, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA. D.M.L. and X.W. thank the support from Advanced Storage Research Consortium (ASRC). The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper. Revisions to this paper have been funded by the Center for Micromagnetics and Information Technologies (MINT). Author contributions: D.-L.Z., J.Z., T.Q., R.H.V., X.W., and J.-P.W. conceived the research. D.-L.Z. designed and prepared all of the samples and carried out all magnetic measurements. J.Z. and D.M.L. designed and carried out the TDTR and TR-MOKE measurements and fitted the data. D.-L.Z. and J.Z. introduced the initial experimental results including magnetic properties and TDTR and TR-MOKE data on this topic to T.Q. and suggested the need for theoretical analysis. T.Q. carried out the theoretical prediction, analytical derivation, and micromagnetic simulation that inspired the experimental results of the resonance. D.-L.Z. and J.Z. participated in the discussion of the theory and micromagnetic simulation. D.-L.Z., J.Z., and T.Q. prepared the figures and drafted the manuscript. J.-P.W., X.W., and R.H.V. coordinated the project. All the authors discussed the results and commented on the manuscript. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.
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