Ferromagnetic-waveguide width dependence of propagation properties for magnetostatic surface spin waves

2021 
The width dependence of propagation properties for magnetostatic surface spin waves (MSSWs) in Permalloy (Py) waveguides was investigated experimentally and numerically. When both the short-side width of a Py waveguide (WPy) and the magnetic field (μ0H) were large enough, the spin wave (SW) intensity almost linearly decreased with decreasing WPy, and the resonant frequency fr was almost independent of WPy. However, when both WPy and μ0H were small, the SW intensity rapidly reduced, and fr decreased with decreasing WPy. Micromagnetic simulations revealed that when both WPy and μ0H are large enough, the magnetization direction of Py is almost parallel to the magnetic field direction, and the SW mode becomes the MSSW mode. In contrast, when both WPy and μ0H are small, magnetization direction tilts to the long-side direction of the Py strip from the magnetic field direction due to a strong demagnetizing field, which is the origin of the unexpected reduction in the intensity and fr. When miniaturized ferromagnetic waveguides are used for shrinking MSSW devices, a sufficiently large magnetic field is necessary because the influence of the shape magnetic anisotropy cannot be ignored.
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