Mode interference and periodic self-focusing of spin waves in permalloy microstripes

We have studied propagation of spin waves in transversally magnetized permalloy microstripes. Our findings show that the interference of spin-wave modes quantized in the direction perpendicular to the stripe axis leads to a spatial pattern characterized by a periodic concentration of the spin-wave energy in the middle of the stripe, which can also be considered as a periodic self-focusing of spin waves. We present a simple model connecting the spatial period of the interference pattern with the width of the stripe and the spin-wave frequency. The studied phenomenon can be used for efficient transmission and processing of microwave-frequency signals by means of spin waves on the nanometer scale.