Nanomagnonics from In-Plane to Out-of-Plane

Qi Wang, University of Vienna

March 29, 2022

Magnonics addresses the physical properties of spin waves and utilizes them for data processing [1-2]. Nano-magnonics addresses the investigation of spin waves in magnetic nanostructures of minimal sizes of a few hundred nanometers or less. Such sizes allow for a qualitative change in the magnon dynamics and allow for: (i) single-mode dispersion curve, (ii) the phenomenon of exchange unpinning resulting in the uniform profiles of magnon modes in them, and (iii) the suppression of parasitic multi-magnon scattering.

In the first half of my talk, I will present briefly the experimental realization of a nanoscale magnonic directional coupler, which consists of two separated single-mode waveguides with a width of 350 nm. A U-shaped antenna is used to excite spin waves and microfocus Brillouin Light Scattering (mBLS) spectroscopy is exploited for detection. After that, I will present the method of inverse-design magnonics, in which any functionality can be specified first, and a feedback-based computational algorithm is used to obtain the device design [3]. To demonstrate the universality of this approach, we explore linear, nonlinear and nonreciprocal magnonic functionalities and use the same algorithm to create a magnonic (de-)multiplexer, a nonlinear switch and a circulator.

In the second part, I will present a new approach to excite exchange spin waves with a wavelength down to around 200 nm in a 200 nm-wide yttrium iron garnet waveguide with a 2 mm-wide antenna. The physical concept of the proposed method is based on the nonlinear phenomena that can be observed in the normally-magnetized waveguides. By using mBLS spectroscopy, we observed an unprecedented 2.1 GHz up-shift of the FMR frequency. The analytic calculations and micromagnetic simulations show that such a huge nonlinear frequency shift provides a large wavenumber conversion of up to 30 rad/mm in k-space for spin waves propagating away from the antenna. The proposed method removes the wavelength limitations imposed by the size of antennas and allows for direct integration on-chip.

[1] A. V. Chumak, et al., IEEE Trans. Magn. 2 (2022). DOI: 10.1109/TMAG.2022.3149664
[2] Q. Wang, et al., Nat. Electron. 3, 765 (2020).
[3] Q. Wang, A. V. Chumak, P. Pirro, Nat. Commun. 12, 2636 (2021).