Strongly coupled magnon hybrid systems with permalloy thin films¹

Recently, magnon-based hybrid systems have attracted increasing interests as a new branch in spintronics research^2-5. Magnons can be coupled to a wide variety of excitations including microwave photons, optical photons, phonons, and other magnons. In addition, the excitation frequency of magnons can be easily tuned by an external magnetic field, which is highly desirable for controllable hybrid systems. Up to date, most studies are based on low-damping yttrium ion garnet (YIG) spheres or thick films, which are beneficial for strong coupling strength but unfavorable for scalable on-chip-integrated applications.

In this talk, we will explore the use of permalloy (Ni₈₀Fe₂₀) thin films in hybrid magnon systems. Permalloy is a classical metallic ferromagnet with well-known magnetic dynamic properties and is easy to grow and integrate into complex devices. In the first part, we demonstrate strong coupling of magnons in a permalloy thin-film device to the microwave photons in a coplanar superconducting resonator⁶, via magnetic dipolar interaction. In the second part, we show strong coupling of permalloy magnons to the spatially nonuniform magnon modes of a YIG film via interfacial coupling⁷. Besides the interfacial exchange coupling acting as a field-like torque, we also show evidence that spin pumping creates a damping-like coupling torque. This torque leads to an increase in line width for the out-of-phase hybrid mode and a reduction for the in-phase hybrid mode. Our results provide new pathways for implementing on-chip magnonic devices with efficient and coherent information transducers.