Spin waves on the nanoscale: non-linear processes and mechanical excitation

Frequency multiplication and frequency conversion are important processes in modern electronics in which harmonics of the input frequency are generated in non-linear electronic circuits. Devices based on the propagation and interaction of spin waves represent a promising alternative to conventional electronics. However, the characteristic frequency of spin waves is in the gigahertz range, and thus cannot be easily combined with conventional electronics. We study magnetic excitations in magnetic materials using optical methods and show that excitation at frequencies in the megahertz range can cause magnetic switching processes triggering coherent spin wave
emission in the gigahertz range [1]. Moreover, at high modulation amplitudes, we demonstrate a new class of nonlinear spin waves that oscillate with half-integer harmonics of the excitation. Imaging of these parametrically generated spin waves enables measurement of the wave vectors and determination of the coherence properties [2]. In addition, we demonstrate the existence of degenerate phase states, each of which can be selected by the phase of an external signal source. Finally, we discuss how spin waves are can be excited mechanically using mageto-elastic coupling. Here, we used surface acoustic waves and nanoscale magnetic structures. We demonstrate that this geometry allows for the excitation to spin waves with almost arbitrary wave vectors.

References
[1] C. Koerner, R. Dreyer, M. Wagener, N. Liebing, H.G. Bauer, G. Woltersdorf, Science 375,
(2022) 1165.
[2] R. Dreyer, A. F Schäffer, H. G. Bauer, N. Liebing, J. Berakdar, and G. Woltersdorf, Nat.
Commun. 13, (2022) 4939