Study of Charge, Spin and Orbital States in Novel Transition-Metal Oxides Using X-Ray Absorption Spectroscopy

Transition-metal compounds show a wealth of intriguing properties such as superconductivity, piezoelectricity, giant magnetoresistance, spin and metal-insulator transitions, which are governed by the interplay of charge, spin, and orbital degrees of freedom. The knowledge of their electronic structure is crucial for understanding and predicting the fascinating properties of these often strongly correlated materials. In this thesis x-ray absorption spectroscopy including x-ray magnetic circular dichroism is combined with theoretical calculations to investigate the orbital occupation and orbital ordering of La4Ru2O10, which shows a 4d orbital-ordering transition with spin-gap opening due to spin-singlet formation, and of Ca2RuO4 for which the orbital occupation across phase transitions have been studied. The valence state, spin state and orbital moment has been studied for Ca3Co2O6, which have peculiar step-wise jumps in the magnetization, and in Ca3CoRhO6 and Ca3FeRhO6. For LaMn0.5Co0.5O3 the valence, spin state, magnetic alignment, and magnetocrystalline anisotropy was investigated