Date of Award


Degree Type


Degree Name

Master of Science




Dr. M. G. Cottam


Motivated by recent experiments, a theoretical study of the nonlinear properties of the spin waves in ferromagnetic nanowires is presented. An ultrathin nanowire is represented by a single line of interacting spins placed in an oblique external applied magnetic field. A Hamiltonian-based approach is followed including terms for the short­ range exchange interactions and the long-range magnetic dipole-dipole interactions. Using a perturbation theory based on a Green’s function formalism and Feynman diagrammatic techniques, the roles of the three-magnon and four-magnon processes are studied. Detailed analytical expressions for the energy shift and damping for three- magnon process are deduced, along with an expression for the four-magnon energy shift in the special case of a longitudinal field. Numerical examples of the theory are made for the spin-wave renormalization effects for various external field orientations, taking

parameters typical of a ferromagnetic metal. Some extensions of the theory to thicker nanowires are outlined



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