Optical frequency combs are well established and powerful tools for synchronization, stabilization and frequency conversion in both fundamental science and technological applications. In this work, we present experimental observations on the generation of spin-wave frequency combs.<br/>Nonlinear four-magnon scattering is known to cause parasitic losses for a driven spin-wave mode with respect to coherence and amplitude. By means of Brillouin light scattering microscopy, we demonstrate that adding a second microwave frequency causes the scattering to populate well-defined states instead of redistributing energy to the entire spin-wave band.<br/>Here, the amplitudes and frequencies of both microwave sources can be utilised in order to tune this behaviour.<br/>When reducing the sizes of the magnetic conduits, lateral confinement causes a discretisation of the eigenmode spectrum. Therefore, the formation of frequency combs can be observed even when driving the conduits into the nonlinear regime by just a single pumping frequency.<br/>The tunability of multimode spin-wave spectra, as demonstrated in our experiments, offers promising technological applications that allow to bridge the frequency gap between CMOS technology and spin waves.

Spin-wave frequency combs

One of the prospects of magnetic nanotubes in magnetization dynamics is using them as waveguides for spin waves. Recently, we have shown that the spin-wave propagation in thin-shell nanotubes with a vortex-state equilibrium magnetization exhibits strongly nonreciprocal spin-wave transport along the nanotube [1,2]. In particular, spin waves with the same wavelength but opposite propagation direction along the tube inherit different oscillation frequencies. This dispersion asymmetry is of dipolar origin and a consequence of the geometrical magnetic pseudo charges induced by the surface curvature of the nanotube. So far, predictions on the spin-wave dispersion in magnetic nanotubes were only available for tubes with a thin shell (with thicknesses comparable to the exchange length of the material) for which the spatial profile of the spin-wave modes can be assumed to be approximately homogenous in radial direction. With the help of our newly-developed finite-element dynamic-matrix approach for spin waves propagating in waveguides with arbitrary cross section [3], we are now exploring the transition of the spin-wave dispersion and mode profiles as the thickness of the nanotube is increased. To this end, we investigate the emergence of spin-wave modes with a standing-wave character along the nanotube thickness. These modes are shown to be strongly hybridized as long as they share the same azimuthal symmetry. Moreover, they correspond to the radial modes in vortex-state disks or to the perpendicular-standing spin waves in magnetic thin films. We present that the dispersion changes drastically as the nanotube-shell thickness is increased. In particular, the dispersion asymmetry increases to the point where there is an almost completely unidirectional propagation similar to the spin-wave transport reported for exchange-coupled bilayers [4].

Spin-wave dispersion in magnetic nanotubes: Beyond the thin-shell approximation

Spin waves (or magnons) in a micrometer-sized disk magnetized in the vortex state offer an ideal playground to investigate nonlinear magnetization dynamics. In the past, we demonstrated that the radial spin waves in a vortex, once excited above their instability threshold decay into secondary azimuthal modes due to highly efficient spontaneous three-magnon splitting in a rich variety of scattering channels [1]. Here, we present a combined numerical, theoretical and experimental study on nonlocal stimulated splitting in a magnetic vortex disk. We show that three-magnon splitting can be triggered below the threshold of spontaneous splitting by coupling the magnetic vortex to magnons propagating in an adjacent waveguide. Furthermore, using nonlinear spin-wave theory and time-resolved Brillouin-light-scattering experiments we demonstrate that stimulated scattering can be used to manipulate the time scales of nonlinear magnetization dynamics. We believe that the possibility to actively control three-magnon splitting in confined magnetic elements could provide a way to use magnon-based nonlinear networks as hardware e.g. for neuromorphic computing. Financial support by the Deutsche Forschungsgemeinschaft within programmes SCHU 2922/1-1 and KA 5069/1-1 is gratefully acknowledged.References: [1] K. Schultheiss, et al. PRL 122, 097202 (2019) [2] L. Körber, et al. arXiv:2005.12663 (submitted)

Nonlocal stimulation of three-magnon splitting in a magnetic vortex

**Session chair:** Axel Hoffmann, University of Illinois at Urbana-Champaign


HOI - Magnonic Crystals and Magnons

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

2022 Joint MMM-INTERMAG

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

**Session chair:** Yi Li, Argonne National Laboratory


HOJ - Magnons and Spin Waves

E4: Spin Wave I: Spatial and Nonlinear Behavior

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

We were reluctant to give up the benefits of meeting face-to-face, and know that shifting to a virtual conference is a significant change for this community. Nevertheless, we are first and foremost concerned about the health and safety of all our Conference participants and their loved ones on returning home after travelling.

The MMM 2020 Steering Committee was working exceptionally hard, along with our sponsors, the IEEE Magnetics Society and AIP Publishing, to make this event serve the needs of our participants, who live in time zones all around the globe, in the best possible way. 

You need a ticket to explore this event.

If you have already registered for MMM 2020, and you have already created an account, then you
just need to login (above).

If you have already registered for MMM 2020, but you have not yet created an account, then you
need to click on &quot;create an account&quot; (above) and then login.

Forgot your password? Go to
https://www.underline.io/log-in

If you have not yet registered for MMM 2020 but would like to do so, go to
https://magnetism.org/register

Still need help? Contact our team!


Lukas Körber

3

8

SHORT BIO

Presentations

Spin-wave frequency combs

Spin-wave dispersion in magnetic nanotubes: Beyond the thin-shell approximation

Nonlocal stimulation of three-magnon splitting in a magnetic vortex

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES