Band structure of magnonic crystals with defects: Brillouin spectroscopy and micromagnetic simulations

Using Brillouin spectroscopy, an observation has been made of the band structures of nanostructured defect magnonic crystals. The samples are otherwise one-dimensional periodic arrays of equal-widthNi(80)Fe(20) and cobalt nanostripes, where the defects are stripes of a different width. A dispersionless defect branch emerges within the band gapwith 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 band gaps and the frequency-dependent localization of the defect mode in the vicinity of the defects.