Dynamics of open and closed classical and quantum-mechanical spin systems

Abstract

This thesis is dedicated to the theoretical and practical understanding of different influences of interactions on the statical and dynamical properties of classical and quantum spin systems. Systems of interest have been finite temperature arrays of dipolarly coupled superparamagnetic nanoparticles with uniaxial anisotropy, spin chains with short and long range exchange or dipolar interactions, as well as coupled and diagonalized quantum spins in an infinitely large environment at zero temperature, leading to relaxation behavior for the spin system.

For the case of the coupled nanoparticles, finite temperature Langevin spin dynamics in the form of stochastic Landau-Lifshitz-Gilbert-Equation simulations were employed and supplemented with analytic modelling of the phase space. The investigation of the spin chains was realized by both spin dynamical and Monte Carlo simulations as well as analytical calculations for the prediction of collinear and non-collinear ground states of the chains. Finally, the study of the relaxation behavior of isolated and coupled quantum spins in a thermal environment was described by a non-Hermitian Hamiltonian generator for the dynamics of pure quantum states.