Figure 3: Experimental demonstration of frequency inversion by the dynamic magnonic crystal.

(a) When the carrier frequency of the incident spin-wave signal packet is detuned from the resonance value of 6,500 MHz (the bandgap centre frequency), the frequency of the reflected signal is inverted about this value (left ordinate axis, red diamonds). The solid red line is the theoretical curve of equation (2). The efficiency of the reflection process (right ordinate axis, blue circles) is maximum at the resonance condition and decreases symmetrically with detuning. (b) Two-dimensional map of reflected signal spectra as a function of the incident signal carrier frequency f_S (31 spectra taken at 1 MHz intervals of f_S). Dark red is indicative of the highest signal intensities, dark blue the lowest; the intervening colour scale is linear. Frequency inversion is clearly demonstrated by the diagonal stripe of high signal intensity with a negative slope (running from the upper left to the lower right corner of the figure). The weak diagonal stripe with a positive slope (from the lower left to the upper right corner) is due to weak conventional (that is, frequency conserving) reflection from inhomogeneities in the spin-wave waveguide.