  Using Brillouin spectroscopy, the first observation has been made of the band
structures of nanostructured defect magnonic crystals. The samples are
otherwise one-dimensional periodic arrays of equal-width Ni80Fe20 and cobalt
nanostripes, where the defects are stripes of a different width. A
dispersionless defect branch emerges within the bandgap with a frequency
tunable by varying the defect stripe width, while the other branches observed
are similar to those of a defect-free crystal. Micromagnetic and finite-element
simulations performed unveil additional tiny bandgaps and the
frequency-dependent localization of the defect mode in the vicinity of the
defects.
