Congratulations to David Osuna, whose paper, ‘Time-domain imaging of curling modes in a confined magnetic vortex and a micromagnetic study exploring the role of spiral spin waves emitted by the core’, was published this month in Physical Review B. David has recently finished his PhD in the CDT and is now a postdoctoral research fellow at University of Exeter, as part of the Electromagnetic and Acoustic Materials Group (EMAG).
David explains the paper’s topic:
“This was a very fruitful collaboration with Dr. Paul Keatley, finally published after about 3 years of hard work!
Generally speaking, we have modeled and ‘filmed’ oscillations of the atomic magnetic spins in microscopic magnets and related them to other dynamics revealed from simulations. Understanding this type of dynamics as a whole is key to design spintronic devices, that may be essential for processing information in quantum computers, for example.
The curling spin wave modes of a ferromagnetic vortex confined to a microscale disk have been directly imaged in response to a microwave field excitation using time-resolved scanning Kerr microscopy. Micromagnetic simulations have been used to explore the interaction of gyrotropic vortex core dynamics with the curling modes observed in the region of circulating in-plane magnetization. Hybridization of the fundamental gyrotropic mode with the degenerate, lowest frequency, azimuthal modes has previously been reported to lead to their splitting and counterpropagating motion, as we observe in our spectra and measured images. The curling nature of the modes can be ascribed to asymmetry in the static and dynamic magnetization across the disk thickness, but here we also present evidence that spiral spin waves emitted by the core can influence the spatial character of higher frequency curling modes for which hybridization is permitted only with gyrotropic modes of the same sense of azimuthal motion. While it is challenging to identify if such modes are truly hybridized from the mode dispersion in a confined disk, our simulations reveal that spiral spin waves from the core may act as mediators of the interaction between the core dynamics and azimuthal modes, enhancing the spiral nature of the curling mode. At higher frequency, modes with radial character only do not exhibit marked curling, but instead show evidence of interaction with spin waves generated at the edge of the disk. The measured spatiotemporal character of the observed curling modes is accurately reproduced by our simulations, which reveal the emission of propagating short-wavelength spiral spin waves from both core and edge regions of the disk. Our simulations suggest that the propagating modes are not inconsequential, but may play a role in the dynamic overlap required for hybridization of modes of the core and in-plane magnetized regions. These results are of importance to the fields of magnonics and spintronics that aim to utilize spin wave emission from highly localized, nanoscale regions of nonuniform magnetization, and their subsequent interaction with modes that may be supported nearby.