Frequency dependence of spin relaxation in periodic systems

In the presence of a periodic scattering potential the spin relaxation in ultrathin ferromagnets is not a monotonous function of the frequency. The spin relaxation rate is found to substantially increase at characteristic frequencies related to the periodicity of the magnon scattering potential (see Fig. 1). This is experimentally confirmed in Ni80Fe20 thin films by artificially introducing different scattering periodicities [1]. The lateral struvturing of the thin film is achieved by Cr+ ion implantation with at an energy of 5 keV and a fluence of 5 × 10E15 ions/cm2 through a 100 nm thick polymethyl methacrylate (PMMA) resist covering the whole sample area. Electron beam lithography was used to fabricate 1 mm long-stripes of width s0 and spacing s1 (i.e., with periodicity l = s0 + s1) within the PMMA resist so that the surface becomes Cr-implanted in a stripewise manner. Frequency dependent Ferromagnetic resonance spectroscopy reveals that the magnetic damping may be increased at specific frequencies by a factor of up to 100%.
This work is supported by the DFG, SFB 491, Grants No. FA 314/6-1 and No. FA 314/3-2.
[1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)