Ordering and dynamics of strongly correlated transition metal oxides

This thesis describes a series of synchrotron based X-ray experiments on the lattice dynamics \nor magnetic ordering of several strongly correlated electron systems. Firstly, it will \nprovide an introduction to the strongly correlated electron materials that were studied. \nAfter which a description of the experimental techniques used, specifically resonant X-ray \nscattering (RXS) and X-ray inelastic scattering (IXS), will be given. Finally the results \nof these experiments will be set out and evaluated. The experiments were as follows: \nX-ray inelastic scattering measurements on the effects of fluorine doping on the lattice dynamics \nof the newly discovered iron pnictide superconducting compound, SmFeAsO0.6F0.35 \nand its antiferromagnetic parent compound, SmFeAsO. The results from these experiments \ndemonstrate the importance of antiferromagnetic fluctuations in understanding the lattice \ndynamics of this class of crystals. This result has been demonstrated for the ‘122’ class of \npnictide crystals, but until now has not been shown for the ‘1111’ class of pnictides. \nResonant X-ray scattering in the vicinity of the Mn L2 and L3 resonant enhancements \nwas used to reassess the magnetic structure of multiferroic TbMnO3. The results indicate \nthat the commonly accepted magnetic structure is modified, with additional a and c axis \nmagnetic components. Therefore the ferroelectric polarisation in TbMnO3 arises from a \nphase transition between two non-collinear magnetic structures. It was previously believed \nthat this phase transition was between a collinear and a non-collinear magnetic structure. \nResonant X-ray scattering measurements were also taken on TbMnO3’s sister compound, \nDyMnO3. Data was recorded at the Mn K and Dy L3 resonant enhancements. Several \nunidentified incommensurate reflections, independent of this compound’s magnetic phases, \nwere detected with photon energies close to the Mn K edge. What these reflections represent \nis still a mystery, although they do make a compelling case for further experimental \nwork.