Phonon dispersion relations and mode displacement profiles. (a) Phonon dispersion relations of the Py/BARC magphonic crystal. Experimental and theoretical data are denoted by dots and solid lines, respectively. Red-dashed lines and magenta-dotted lines represent the simulated Rayleigh wave (RW) and Sezawa wave (SW) dispersions for the effective medium film on Si(001) substrate. The transverse (T) and longitudinal (L) bulk wave thresholds are represented by respective green dot-dashed lines and blue short-dot-dashed lines. Measured Bragg gap opening and the hybridization bandgap are indicated by a pink rectangle and a yellow band, respectively. z-components of the displacements of observed phonon modes at (b) q = π/a and (c) q = 1.4π/a.