Spin and orbital degrees of freedom in transition metal oxides and oxide thin films studied by soft x-ray absorption spectroscopy

Abstract

The class of transition metal compounds shows an enormous richness of physical properties, such as metal-insulator transitions, colossal magneto-resistance, super-conductivity, magneto-optics and spin-depend transport. It now becomes more and more clear that in order to describe transition metal compounds the charge, orbital, spin and lattice degrees of freedom should all be taken into account. With the recognition that the local orbital occupation plays an important role in many of the transition metal compounds there is a need for experimental techniques that can measure the orbital occupation. This technique is soft x-ray absorption spectroscopy. Within this PhD. Thesis we will illustrate the usefulness of this technique by some examples: 1) Magnetic versus crystal-field linear dichroism in NiO thin films. 2) The importance of spin-orbit coupling in CoO bulk and CoO thin films. 3) Aligning spins in anti ferromagneticfilms using antiferromagnets. 4) The spin-state puzzle in the cobaltates. 5) Determination of the orbital momentum and crystal-field splitting in LaTiO3. 6) Orbital-assisted metal-insulator transition in VO2.