Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

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 scattering centers for spin waves. 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 processes. We present, that the uniform resonance mode splits into several modes and we compare the experimental results with analytical theory and simulations.
The periodically perturbed films are the intermediate step in the transition from a planar film towards full magnonic crystals. Small magnetic perturbations can be achieved by magnetic patterning using ion beam implantation [2]. A lithographically defined mask (stripes, dots, squares, …) covers part of the sample. Thus, these areas are protected from the ion beam changing the magnetic properties in the surface region of the sample creating magnetic defects. Another method we apply is to use ion etching to mill the pattern into the magnetic film to create geometric defects. Both techniques allow for precise control of the defect depth. With the latter approach the defect depth can be increased reaching the substrate, such that the structures are finally separated resembling a 1D or 2D magnonic crystal.
The evolution of spinwave modes and magnon bands in this transition from just a perturbation to a magnonic crystal has not been investigated so far.The extended model allows for analytically calculating the response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments as it will be shown. A striking feature e.g. is the level splitting due to the two-magnon scattering, which even leads to magnonic band gaps in full magnonics crystals. Exactly this splitting can be tailored by the geometric and magnetic sample parameters as described above.

This work was supported by the DFG grants FA 314/6-1 and FA314/3-2, as well as by CONICYT and MECESUP FSM0806.