Ferromagnetic relaxation and interlayer exchange coupling in magnetic films and heterostructures

Magnetic thin films and heterostructures have attracted a great deal of attention recently from both fundamental and technological prospectives. This thesis focuses on the theoretical investigation of ferromagnetic relaxation in thin metallic multilayers, and oscillatory interlayer coupling in half-metallic oxide multilayers. The intrinsic damping mechanism arising from the magnon-magnon scattering is theoretically studied in 3D and 2D ferromagnets. We develop an analytic theory, which identifies the 3-magnon (in bulk) and 4-magnon (in thin films) scattering processes, responsible for rapid relaxation. Micromagnetic simulations are used to confirm the analytic theory predictions, and to investigate the damping in different realistic technologically important systems. For large angle rotation of magnetization this intrinsic mechanism can dominate competing linear mechanisms even for rapidly relaxing metals. Another important damping mechanism is caused by surface roughness induced 2-magnon scattering. An approximate analytical solution predicts non-exponential decay of the uniform precession excitations. This behavior, as well as the dependence of the decay time on film and roughness parameters are confirmed by micromagnetic simulations. The interlayer exchange coupling is investigated in magnetic oxide heterostructures. The ferromagnetic layer material La2/3 Ba1/3MnO3 belongs to the family of metallic manganese oxides that exhibit colossal magnetoresistance (CMR) and are believed to be half-metallic. Analyzing the hysteresis loops of the superlattices and spin-valve structures, we have demonstrated that the initially antiferromagnetic coupling becomes ferromagnetic at larger spacer thicknesses. This behavior is explained within the RKKY model employing an ab initio calculated band structure of LaNiO3. A conventional RKKY model with additional damping caused by strong electron scattering in the nonmagnetic layer has been used to describe the observed variation of the coupling. The nested-like feature of the LaNiO 3 Fermi surface determines the phase and period of interlayer exchange coupling, while the strong scattering of electrons off defects in LaNiO3 accounts for the rapid damping of oscillations. The experimental and theoretical results agree reasonably well.