Magnetization Dynamics in Magnetically Coupled Heterostructures

This thesis focusses on the influence of interlayer coupling on the magnetization dynamics of heterostructure systems. This topic has been investigated by time-resolved\nphotoemission electron microscopy (PEEM) using a pump-probe approach. Magnetic and chemical contrast is provided by the llumination with circularly polarized x-rays\ndue to the x-ray magnetic circular dichroism (XMCD) effect. In this way the spatially\nresolved magnetodynamic response of the single layers in asymmetric trilayer\nsamples on short magnetic field pulses was studied . The measurements have been\ncarried out at the electron storage rings ESRF (Grenoble) and BESSY-II (Berlin).\nSamples with different material combinations have been deposited by molecular beam\nevaporation (MBE) and magnetron sputtering and subsequently micro-structured by\noptical lithography and Argon ion beam milling. Combining PEEM and magnetooptical\nKerr effect (MOKE) studies the coupling conditions have been investigated.\nIn CoFe/Cr/ NiFe and Fe/Cr/Co systems oscillatory interlayer exchange coupling\ndepending on the Cr spacer thickness was found, while the Heusler-based Co2MnSi/\nMgO/Co2FeSi system showed a roughness-induced orange-peel coupling.\nTime-resolved measurements have been carried out on single films and interlayer exchange coupled trilayers. In single-crystalline iron films the influence of the agnetocrystalline anisotropy on the magnetodynamic response was studied. A bulging of the domain walls was found experimentally and in micromagnetic simulations.\nThis effect is discussed in terms of an inhomogeneous demagnetizing field within\nthe magnetic elements. In heterostructures the competition between single film properties such as shape and magnetocrystalline anisotropy and the interlayer exchange coupling was studied. The single films showed an inhomogeneous response with a locally varying coupling strength due to locally enhanced magnetic stray fields at domain walls or defects. The results are discussed in terms of the local energy contributions.\nBy varying the temporal shape of the excitation field different magnetodynamic\nreactions have been investigated. Using short magnetic field pulses magnetic\neigenmodes have been excited that have been reproduced by macro-spin calculations.\nThe frequency of the eigenmode was found to be considerably increased due to the\ninterlayer coupling.