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ISBN 978-3-8439-0295-3

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978-3-8439-0295-3, Reihe Physik

Alexander Christian Herzog
Magnetic excitations in spin-orbital models and frustrated spin chains

149 Seiten, Dissertation Technische Universität Kaiserslautern (2011), Softcover, A5

Zusammenfassung / Abstract

In this thesis I am concerned with the theoretical description of the magnetic properties of transition metal oxides. After a brief introduction about the principles of magnetic interactions we discuss the physical situation in several solid state compounds which we classify as Mott and charge-transfer insulators respectively. The description of low- energy excitations in these systems is given by means of effective spin models, which are motivated on the basis of the specific configurations of the compound under consideration. In particular we focus on models where it can be assumed that the magnetic interactions are restricted to one dimension. We investigate frustrated and dimerized spin chains which exhibit a ferromagnetic ground state. Furthermore we give a detailed discussion about spin-orbital systems where the effective model incorporates a close interplay between the spin and the orbital degrees of freedom. The analytical description of the spin degree of freedom is mainly discussed by means of the modified spin wave theory. Within this approach a magnetic excitation is described as the creation of a magnon where a chemical potential ensures the absence of spontaneous long range order in the system. We exemplify this well-known method for the one-dimensional ferromagnetic Heisenberg model. In addition we point out novel aspects of the theoretical description of neutron scattering experiments in this system.