Two-Magnon Scattering in the Transition from Periodical Perturbations to Magnonic Crystals

Two-magnon scattering is a well-known effect e.g. in ferromagnetic resonance (FMR) experiments leading to a linewidth broadening. Available theory so far was based on random defects acting as a dipolar scattering potential. Recently it was shown by Landeros and Mills [1] that this theory can be extended to handle two-magnon scattering in periodically perturbed films, which can be easily created by lithographical patterning. These perturbed films are the intermediate step towards full magnonic crystals.
The extended model allows for analytically calculating the resonance response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments [2,3]. The scattering potential of the defects builds up due to the dipolar stray fields at the edges of the defects. Within the perturbation theory this leads on the one hand to a shift of the resonance peak and on the other hand also to a splitting of the uniform resonance mode. Both effects are clearly visible in the FMR experiments. The mode splitting due to the two-magnon scattering finally is also responsible for the opening of magnonic band gaps in the dispersion relation of magnonic crystals. The splitting can be tailored by the geometric and magnetic sample parameters. Experimental data for magnetically patterned stripe samples as well as for ripple samples [3] is presented and compared to calculations by the analytical model (see e.g. Fig. 1).
This work was supported by the DFG grants FA 314/6-1, FA314/3-2.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, K. Lenz, A. Banholzer, M. Körner, J. Lindner, J. Fassbender, P. Landeros, Phys Rev. B (2013) submitted
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner, P. Landeros, J. Fassbender, Phys. Rev. B (2013) submitted