Magnon-photon coupling between a superconducting resonator and a thin film permalloy stripe

Coherent processing of magnetic excitations has received increasing attentions for spin-wave-based functionality such as magnonics, cavity spintronics and quantum information processing. They usually involve strong coupling of different excitations, such as magnons and photons, which leads to their hybridized modes.

In this work, we achieve strong magnon-photon coupling of a device ferromagnet of Ni₈₀Fe₂₀ (Py) to a high-quality NbN coplanar superconducting resonator. Microwave characterizations at 1.6 K show a high quality factor Q~10000. A Py 30 nm stripe was then fabricated on top of the resonator with a 10-nm MgO spacer. We observe a strong anti-cross between the superconducting resonator mode and the Kittel mode of the Py stripe. A maximum coupling strength of g_eff=100 MHz is obtained at about 5 GHz when the biasing field is orthogonal to the microwave field from the resonator. The anti-crossing is completely suppressed when the biasing field is parallel to the resonator microwave field. Our results provide new pathways for implementing on-chip magnonic devices with efficient and coherent information transducers.