Exchange Cavity Magnon-Polaritons in Metallic Thin Films*

Cavity magnonics has become an intriguing field of research due to its potential to enable next-generation technologies. The advent of such technologies centers around controlling information exchange in hybrid resonant systems. Investigating the tunable nature of magnon-photon coupling, and the critical effects of dissipation, are key to advancing the field. However, study of dissipation variations for different magnon modes is rare in the context of cavity dynamics, where works have so far addressed the effect of milli-Kelvin temperatures on magnetic spheres [1]. Here we report on the observation of coupling between the first-order exchange magnon mode in metallic thin film Permalloy (Py) with a cavity photon mode at room temperature. We utilise an electromagnetic perturbation theory that takes account of standing spin waves and their respective variation in dissipation, while estimating coupling strength. In contrast to widespread magnetic insulators such as Yttrium Iron Garnet (YIG), in metals like Py at 100nm and above, the first-order magnon mode exhibits far lower dissipation than the Kittel mode, something which has been observed in previous studies in isolated Py systems [2]. With potential for application in quantum information science and engineering, taking advantage of the magnon dissipation of different modes may offer new opportunity for controlling the flow of microwave photons with a single field-switchable thin film device.

[1] npj QI 1, 15014 (2015)

[2] PRL 116, 117602 (2016)