Computersimulationen zur Struktur und Dynamik von Domänenwänden

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SCHIEBACK, Christine, 2010. Computersimulationen zur Struktur und Dynamik von Domänenwänden

@phdthesis{Schieback2010Compu-9098, title={Computersimulationen zur Struktur und Dynamik von Domänenwänden}, year={2010}, author={Schieback, Christine}, address={Konstanz}, school={Universität Konstanz} }

application/pdf Schieback, Christine deu Computer simulations of domain wall structures and dynamics In this thesis magnetic domain walls in laterally confined ferromagnetic elements are studied, as well as the influence of a spin polarized current on domain wall motion (spin transfer torque effect). One important aspect is the impact of finite temperatures on domain walls. Computer simulations based on a classical extended Heisenberg approach are performed. Furthermore, a novel micromagnetic macrospin model for finite temperatures (Landau-Lifshitz-Bloch equation) is employed.<br />In magnetic nanostructures constrictions are a useful tool to position and manipulate domain walls. In this thesis we investigate the spin structure of domain walls in constrictions down to widths of 20nm at zero Kelvin. Depending on the details of the geometry, two types of domain walls, symmetric and asymmetric walls, are observed. In order to analyze the spin structures an opening angle of the domain wall is introduced and an average domain wall width is calculated.<br />Within the framework of the Landau-Lifshitz-Bloch equation derived by Garanin domain walls in Permalloy nanorings are investigated at finite temperatures. Vortex domain walls can be found in more narrow rings than in comparison to results of micromagnetic simulations at zero Kelvin. This trend is also observed in existing experiments performed at room temperature.<br />Apart from the influence of geometry on the domain wall structure current-induced domain wall motion is investigated. Rather than conventional micromagnetic methods, we use an extended classical Heisenberg spin model approach, which is well suited to study domain walls at elevated temperatures. We compute the behavior of domain walls in a one dimensional chain for the cases, that currents are injected using adiabatic and non-adiabatic spin torque terms. It is found that the influence of thermal fluctuations is pronounced close to the critical effective spin current, respectively close to the Walker threshold. The behavior observed depends strongly on the value of the nonadiabatic prefactor. For the adiabatic case as well as the nonadiabatic cases with nonadiabatic prefactors smaller than the Gilbert damping constant the domain wall velocities increase with increasing temperature. In contrast the domain wall velocities decrease with increasing temperature for cases with nonadiabatic prefactors larger than the Gilbert damping constant.<br />Furthermore current-induced domain wall motion is studied at finite temperatures using micromagnetic simulations. For this purpose we extend the Landau-Lifshitz-Bloch equation of motion by adding an adiabatic and nonadiabatic spin torque term. Here, the spin torque terms are now temperature dependent. We investigate analytically as well as numerically domain wall motion at various temperatures for the adiabatic and nonadiabatic cases. The Walker threshold as well as the domain wall velocities show a strong temperature dependence. Furthermore a different behavior is found for the temperature-dependent Walker threshold and domain wall velocities assuming the Gilbert form of damping or the Landau-Lifshitz form. Schieback, Christine 2011-03-24T17:53:36Z 2011-03-24T17:53:36Z Computersimulationen zur Struktur und Dynamik von Domänenwänden deposit-license 2010

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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