The role of the internal demagnetizing field for the dynamics of a magnonic crystal

Magnonic crystals with locally alternating properties and specific periodicities exhibit interesting effects, such as a multitude of different spin-wave states with adjustable band gaps. This work aims for demonstrating and understanding the key role, which local demagnetizing fields play in such systems. In order to get direct access to this matter, the spin-dynamics of a magnonic crystal were reconstructed from ‘bottom-up’, i.e. the structural shape as well as the internal field landscape of the structure were experimentally reconstructed on the nanoscale using electron holography. Subsequently, both properties were utilized to perform dynamic response calculations. The simulations yield the frequency-field dependence as well as the angular dependence of spin waves in a magnonic crystal and reveal the governing role of the internal field landscape around the backward-volume geometry. Connecting the internal field landscape with the individual spin-wave mode localization, a comprehensive model is presented describing the complex angle-dependent spin-wave behavior around 360◦ rotation of an in-plane external field. A significant spin-wave propagation is reported for a broad angular range around the Damon-Eshbach geometry.