Efficient generation of second-harmonic propagating spin waves in an out-of-plane-magnetized thin ferromagnetic film
Phys. Rev. Applied 25, 054072 – Published 28 May, 2026
DOI: https://doi.org/10.1103/xxlw-pnhs
Abstract
Spin waves are attractive information carriers, owing to their gigahertz-to-terahertz frequencies, nanometric wavelengths, and negligible Joule heating. However, efficiently and locally exciting short-wavelength high-frequency propagating spin waves and exploiting nonlinear effects remain challenging. We propose a hybrid ferromagnetic structure consisting of an in-plane-magnetized nanosized area (a magnonic nanocavity) that is exchange-coupled to an out-of-plane-magnetized film or stripe. Micromagnetic simulations show that a spatially uniform out-of-plane microwave magnetic field excites only the fundamental mode of the nanocavity. Its second harmonic is then coherently and efficiently launched into the extended part of the ferromagnet, yielding propagating spin waves. This process can be achieved with stripe or extended film geometries, which excite plane waves or radial spin waves, respectively. Given the simple fabrication process of degrading the anisotropy of a ferromagnetic layer with perpendicular magnetic anisotropy, the spin-wave wave front can be shaped extensively by adjusting the nanocavity geometry. Conversion efficiency can be enhanced when the frequency of the second harmonic matches a higher-order standing spin-wave frequency of the nanocavity. Furthermore, the emission frequency is tunable via the bias magnetic field or the width of the nanocavity. These findings suggest a compact route toward on-chip, short-wavelength, high-frequency nonlinear spin-wave sources for artificial neural networks.
