Abstract

Magnonics, an emerging field of magnetism, studies spin waves (SWs) in nanostructures, with an aim towards possible applications. As information may be eventually transmitted with efficiency stored in the phase and amplitude of spin waves, a topic of interest within magnonics is the propagation of SW modes. Thus understanding mechanisms that may influence SW propagation is of interest. Here the effect of localized surface geometric defects on magnetostatic surface modes propagation is studied in ferromagnetic films and semi-infinite media. Theoretical results are developed that allow one to calculate the scattering of these surface or Damon-Eshbach (DE) modes. A Green's-extinction theorem extension is used to determine the scattering of incident surface modes through the determination of phase shifts of associated modes that are symmetric and antisymmetric under inversion in the same geometry with geometric defects. Choosing localized symmetric depressions as geometric defects, scattering transmission coefficients are determined that show perfect transmission at specific frequencies or wavelengths that we associate with resonances in the system: they do occur when appropriate fractions of the incoming wavelength "fit" with the approximate depression's sizes, i.e., depressions are effectively similar to "potential wells." Interestingly the system also shows the appearance of localized modes in the depression regions, with associated discrete frequencies immersed in the continuum spectrum of these surface DE modes. These localized modes have a short wavelength content and appear similarly in semi-infinite surfaces with depressions. The latter indicates that these types of scattering effects should appear in all surfaces with roughness or more pronounced geometric defects.