Enhancement of magnonic harmonic signals in the magnetic domain walls

Harmonic generation is a non-linear phenomenon that produces output signals at multiples of the input signal frequency. In attosecond physics, optical high-harmonic generation is a useful tool for generating high-frequency photons from lower-frequency photons. Recently, magnonic harmonic generation has attracted growing attention as a magnonic analog of optical harmonic generation. Magnonic harmonics has been observed up to the 60ths of the pump frequency, detected using NV magnetometry[1]. Such promising results are expected to further enable the development of high frequency magnonic devices for high-speed spintronics applications. Despite its experimental progress, theoretical understanding of magnonic harmonic generation remains incomplete. One example is the strong harmonic signal observed inside the magnetic domain walls, frequently reported in studies using numerical analysis. In this presentation, we discuss the physics underlying the enhancement of the harmonic signal in domain walls. Using a micromagnetic simulation, we first confirm that harmonic generation is amplified within domain walls. We then show that, in the linear regime, domain walls act as effective potential wells for magnons leading to confinement of the first harmonic excitation. Finally, we extend the analysis to the non-linear regime and demonstrate that the higher-order harmonics are likewise expected to be confined to the domain wall region.

[1] C. Koerner, et al. Science 375, 1165-1169 (2022).