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Magnon–fluxon interaction in a ferromagnet/superconductor heterostructure

Abstract

Ferromagnetism and superconductivity are most fundamental phenomena in condensed-matter physics. Entailing opposite spin orders, they share an important conceptual similarity: disturbances in magnetic ordering in magnetic materials can propagate in the form of spin waves (magnons) while magnetic fields penetrate superconductors as a lattice of magnetic flux quanta (fluxons). Despite a rich choice of wave and quantum phenomena predicted, magnon–fluxon coupling has not been observed experimentally so far. Here, we clearly evidence the interaction of spin waves with a flux lattice in ferromagnet/superconductor Py/Nb bilayers. We demonstrate that, in this system, the magnon frequency spectrum exhibits a Bloch-like band structure that can be tuned by the biasing magnetic field. Furthermore, we observe Doppler shifts in the frequency spectra of spin waves scattered on a flux lattice moving under the action of a transport current in the superconductor.

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Fig. 1: Experimental system.
Fig. 2: Fluxon-induced reconfigurable magnonic crystal.
Fig. 3: Tailoring spin-wave spectra by magnetic field and current.
Fig. 4: Doppler shift at Bragg scattering of magnons on moving fluxons.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

The authors gratefully acknowledge financial support by the DFG in the framework of the Collaborative Research Center SFB/TRR-173 Spin+X (Project B04). O.V.D. acknowledges the DFG for support through grant no. 374052683 (DO1511/3-1). O.V.D., V.V.K., R.V.V. and V.A.S. acknowledge support from the European Commission within the framework of the programme Marie Sklodowska-Curie Actions—Research and Innovation Staff Exchange (MSCA-RISE) under grant agreement no. 644348 (MagIC). A.V.C. and T.B. acknowledge financial support within the ERC Starting Grant no. 678309 MagnonCircuits. Research leading to these results was also conducted within the framework of the COST Action CA16218 (NANOCOHYBRI) of the European Cooperation in Science and Technology.

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Contributions

O.V.D., A.V.C., V.V.K. and V.A.S. conceived the experiment. O.V.D. and A.V.C. designed the samples. T.Böttcher and R.S. fabricated the samples. O.V.D. and R.V.V. performed the measurements. O.V.D., T.Brächer and A.V.C. performed and evaluated the spin-wave transmission simulations. O.V.D. and A.V.C. led the project. All authors discussed the results and co-wrote the manuscript.

Corresponding author

Correspondence to O. V. Dobrovolskiy.

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Journal peer review information: Nature Physics thanks Jason Robinson and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Dobrovolskiy, O.V., Sachser, R., Brächer, T. et al. Magnon–fluxon interaction in a ferromagnet/superconductor heterostructure. Nat. Phys. 15, 477–482 (2019). https://doi.org/10.1038/s41567-019-0428-5

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