  In this paper, we theoretically study the influence of a non-magnetic spacer
between ferromagnetic dots and ferromagnetic matrix on the frequency dispersion
of the spin wave excitations in two-dimensional bi-component magnonic crystals.
By means of the dynamical matrix method we investigate structures inhomogeneous
across the thickness represented by square arrays of Cobalt or Permalloy dots
in a Permalloy matrix. We show that the introduction of a non-magnetic spacer
significantly modifies the total internal magnetic field especially at the
edges of the grooves and dots. This permits the manipulation of the magnonic
band structure of spin waves localized either at the edges of the dots or in
matrix material at the edges of grooves. According to the micromagnetic
simulations two types of end modes were found. The corresponding frequencies
are significantly influenced by the end modes localization region. We also show
that, with the use of a single ferromagnetic material, it is possible to design
a magnonic crystal preserving properties of bi-component magnonic crystals and
magnonic antidot lattices. Finally, the influence of the non-magnetic spacers
on the technologically relevant parameters like group velocity and magnonic
band width are discussed.
