Nonlinear magnonics

Magnonics, the study and development of devices utilising collective spin excitations, is a rapidly growing field, covering both fundamental topics (antiferromagnetism, quasiparticle condensates) and technological applications (MRAM, spintronics). We use a host of optical, electrical and x-ray based techniques to study the nonlinear and quantum regimes of magnonics, with the goal of utilising such processes in future magnonic technologies.

spinwaves
Phase resolved measurement of spin waves in YIG. Scanning x-ray microscope images are acquired synchronously with a CW RF excitation. The signal (3.5 GHz) is applied to the sample via a transmission line, exciting spin wave modes according to the external field and resulting dispersion. a) shows a transmission snapshot, the dark region is the RF line, the light grey region is the YIG, with the subtle changes in contrast being dynamic magnetic contrast. b)-f) show the amplitude and phase of the dynamics at the excitation frequency extracted via an FFT and mapped onto the brightness and hue channel in a hue saturation brightness (HSB) colour space.

The study of magnons, the quasiparticle description of collective spin excitations, and magnonics, the development of devices utilizing magnons to perform information processing tasks, are rapidly growing fields covering many important fundamental and technological topics. A frequently proffered advantage of magnonics over conventional electronics is the lack of ohmic losses in the flow of magnons. This advantage is mute however in the presence of other significant dissipative losses such as Gilbert damping. Yttrium iron garnet (YIG), a ferrimagnetic insulating oxide, has long been appreciated in the context of high-Q microwave filters that make use of its sharp ferromagnetic resonance. However, the long magnon lifetime, with damping values up to three orders of magnitude lower than conventional metallic magnetic materials, along with advances in thin film growth and processing capabilities has seen a resurgence of interest in YIG from the magnonics community.  

A phenomena closely linked to the extremely long lifetimes of magnons in YIG is their reported Bose-Einstein condensation (BEC) at room temperature. A finding that has raised many questions about the nature of a quasiparticle BEC in quasi-equilibrium, its relation to traditional BECs familiar from cold atom physics, and other types of macroscopic coherent phenomena. From an applications perspective the incorporation of condensate related phenomena to the magnonics toolbox would open the door to supercurrents of magnons and quantum information processing.  

The goal of this project is to use new x-ray techniques to study such exotic magnonic phenomena with a goal of developing devices. 

Multi-band Bose-Einstein condensate at four-particle scattering resonance
J. Bailey, P. Sukhachov, K. Baumgaertl, S. Finizio, S. Wintz, C. Dubs, J. Raabe, D. Grundler, A. Balatsky, G. Aeppli
arXiv:2201.11043