4 Reports on Experimental Results 4.10 Storage-recovery phenomenon in a magnonic crystal

The deceleration or even the full stop of light due to the modiÞcation of the light dispersion in photonic crystals has been a topic of intense experimental and theoretical studies over the last decade [1, 2]. A wave of light propagating through a photonic crystal couples with the internal standing crystal mode and generates a slow light mode. In terms of the dispersion characteristics this means that the slope of the dispersion curve decreases at the edges of the band gaps which results in an extremely small value of the group velocity. It has been demonstrated that slow light can be used for time-domain processing including buffering (storage and recovery) of optical signals as well as for an enhancement of nonlinear effects due to the spatial compression of optical energy [1, 2]. Magnonic crystals (MCs) are the magnetic counterpart of photonic crystals which operate with spin waves, i.e. the collective oscillations of the spin lattice of a magnetic material [38]. The storage of a spin wave in a magnonic crystal is complicated due to signiÞcant intrinsic spin wave damping which limits the maximum number of structure periods to about 20 (see Ref. [9] and references therein). The small number of periods implies that the slope of the MC dispersion does not become zero at the edges of the magnonic band gap in contrast to the light dispersion at the edges of photonic gaps. Hence, rather than vanishing, the group velocity of spin waves only slightly decreases at the gap edges. Nevertheless, in one of our previous reports [10] we have shown that storage-recovery has been successfully realized in a magnonic crystal. A spin-wave packet propagating through the MC area has been partially stored in it and was recovered after a considerably long time using parametric ampliÞcation. The pronounced recovered signal has been observed for frequencies corresponding to the edges of the magnonic-crystal band gaps. However, in spite of the conÞdent experimental evidences of the signal recovery, the mechanism of the storage itself remained unclear. In this Report we show that unlike the conventional scheme m