  Magnonic crystals with locally alternating properties and specific
periodicities exhibit interesting effects, such as a multitude of different
spin-wave states and large band gaps. This work aims for demonstrating and
understanding the key role of local demagnetizing fields in such systems. To
achieve this, hybrid structures are investigated consisting of a continuous
thin film with a stripe modulation on top favorable due to the adjustability of
the magnonic effects with the modulation size. For a direct access to the spin
dynamics, a magnonic crystal was reconstructed from `bottom-up', i.e., the
structural shape as well as the internal field landscape of the structure were
experimentally obtained 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. The complex angle-dependent spin-wave behavior is described for a 360
degree in-plane rotation of an external field by connecting the internal field
landscape with the individual spin-wave localization.
