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arXiv · 2604.27076

Superconductivity-Enabled Conversion of Ferromagnetic Resonance into Standing Spin Waves

Ya. V. Turkin·N. G. Pugach·F. M. Maksimov·A. S. Pakhomov·S. N. Polulyakh·V. S. Stolyarov·A. I. Chernov·V. I. Belotelov
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Abstract

Superconductors can transport spin without Joule dissipation, yet their coherent coupling to short-wavelength magnons in insulating magnets remains largely unexplored. Here we demonstrate experimentally and theoretically that a conventional diffusive superconductor can enable the conversion of the uniform ferromagnetic resonance (FMR) mode into perpendicular standing spin waves (PSSWs) in an adjacent ferrimagnetic insulator. In Bi-substituted iron-garnet/Nb bilayers, the microwave transmission develops an additional resonance feature that appears only below the Nb superconducting transition temperature and lies close to the uniform FMR peak. A microscopic theory that self-consistently couples the quasiclassical Keldysh--Usadel description of the superconducting condensate to the Landau--Lifshitz--Gilbert dynamics shows that the conversion relies on two ingredients: (i) an interfacial spin-transfer torque mediated by spin-polarized triplet Cooper pairs and (ii) a depth-dependent effective field produced by Abrikosov vortices (electromagnetic proximity). The resulting susceptibility reproduces the measured lineshapes and establishes superconductivity as an active control parameter for exchange standing-wave modes in magnetic insulators.

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Ya. V. Turkin, N. G. Pugach, F. M. Maksimov, A. S. Pakhomov, S. N. Polulyakh, V. S. Stolyarov, A. I. Chernov, V. I. Belotelov. 2026-04-29. Superconductivity-Enabled Conversion of Ferromagnetic Resonance into Standing Spin Waves. https://arxiv.org/abs/2604.27076

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