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Abstract The performance of magnonic devices such as converters, switches, and multiplexers greatly depends on magnonic noise. While a peculiar discrete magnonic noise has been previously reported, the sources of underlying magnon dynamics occurring in high-magnon density conditions have not been clarified. Here, zero-span measurements of the spectrum analyzer were recorded to accurately detect magnonic noise as a fluctuation of the spin-wave amplitude. The results of low-frequency magnonic noise demonstrated a spin-wave mode dependency, indicating the existence of a peculiar magnon surface state. Furthermore, the energy thresholds of four-magnon scattering and autooscillation were determined using magnonic white noise. The noise data obtained in this study can help promote theoretical and experimental research on magnons.

The magnonic functionalities of magnonic devices, such as logic gates, majority gates, and multiplexers, critically depend on anisotropic spin-wave dispersions. Further, each magnonic function utilizes the advantages of distinct spin-wave modes. However, thus far, no method of directly combining magnonic functions to construct an integrated magnonic circuit has been proposed. Therefore, this paper presents a method for the interconversion of surface spin-waves and backward volume spin-waves using a thermoelectrically controlled magnetization gradient. The results of time- and frequency-domain spectroscopies, heat transfer analyses, and micromagnetic simulations demonstrate the effectiveness of the proposed method, through which spin-wave interconversion via thermoelectric control may be employed to develop integrated magnonic circuits.