Morphology induced magnetic anisotropy and damping in thin films

Both, modification of magnetic anisotropy as well as damping, are of fundamental and technological importance. When miniaturizing the dimensions of a magnetic device roughness becomes more and more important, e.g. induced anisotropies have to be taken into account. Additionally new effects like direction dependent, defect induced two-magnon scattering are enabled. This opens the possibility for new types of devices where the damping can be set by an external magnetic field or by frequency.
Broad ion beam erosion is a well-established technique for structuring large scale surfaces. By varying the ion irradiation parameters, e.g. ion energy, fluence, incident angle, and sample temperature sinusoidally modulated surface corrugations (ripples) can be created with a periodicity tuneable over a wide range. Growing magnetic materials on these rippled substrates imprints the surface corrugation to the deposited material and induces a uniaxial magnetic anisotropy (UMA), caused by dipolar effects, where the strength of the UMA is wavelength dependent. On the other hand the imprinted surface corrugation can serve as spin wave scattering center in thin magnetic films, modifying the magnetic damping properties by introducing a two-magnon scattering contribution.
The in-plane anisotropy and damping properties of magnetic films grown on rippled substrates were investigated by means of angular as well as frequency dependent vector network analyzer ferromagnetic resonance. In case of tailoring magnetic anisotropy, the influence of single-crystalline thin iron films epitaxially grown on rippled MgO substrates will be presented. Here a superposition of magneto-crystalline and morphology induced UMA is observed, where the UMA can be set to an arbitrary direction with respect to the crystalline anisotropy. Furthermore the influence of rippled surfaces on thin polycrystalline Ni80Fe20 films will be discussed, where the surface corrugation acts as spin wave scattering center introducing a two-magnon scattering damping contribution. The latter leads to distinct peaks in the frequency dependent linewidth and a uniaxial in-plane damping behavior.