Oliver Pieper

Neutron Scattering Investigations of Zero- and One-Dimensional Quantum Magnets Oliver Pieper

This thesis deals with the investigation of two different types of low-dimensional quantum magnets using the technique of neutron scattering. In the first part, the magnetic properties of three Mn_6-based single molecule magnets are explored by means of inelastic neutron scattering. The experimental data reveal that small structural distortions of the molecular geometry produce a significant effect on the energy level diagram and therefore on the magnetic properties of the molecules. It will be shown that the giant spin model completely fails to describe the spin level structure of the ground spin multiplets and that the excited S-multiplets play a key role in determining the effective energy barrier for the magnetization reversal. The second part of this thesis presents an in-depth study of the nuclear and magnetic properties of the quasi-one-dimensional Heisenberg antiferromagnet CaV2O4. The magnetism in this system arises from the partially filled t2g-levels of the V3+-ions, which in addition give an orbital degree of freedom to the system. Single crystal and powder neutron diffraction as well as neutron spectroscopy are used to determine the nuclear and magnetic structure as well as the complex excitation spectrum of CaV2O4. The results are analysed theoretically and from this the leading exchange paths are deduced and discussed in terms of orbital ordering.