In chapter 2 and 3, using first-principles density functional theory (DFT) calculations, we begin our study of LaAlO3|SrTiO3 (LAO|STO) by reproducing the band insulating states of bulk LAO and STO with a cubic perovskite structure. In the case of LAO thin films grown on STO substrates, alternate stacking of positively (LaO+) and negatively (AlO2-) charged layers on the non-polar STO substrate would give rise to a huge effective internal electric field if both materials kept the initial state and nothing else were to happen. The accompanying electrostatic potential would diverge with increasing thickness of LAO, leading to a polar instability. We demonstrate the internal electric field in terms of core level shifts calculated within DFT that are consistent with a parallel plate capacitor model. In chapter 4, we find a strong position and thickness dependence of the formation energy of oxygen vacancies in LAO|STO multilayers and interpret this with an analytical capacitor model. In chapter 5, using first-principles density functional theory calculations, we predict GdFeO3-like rotation of TiO6 octahedra at the n-type interface between cubic pervoskite LAO and STO. In chapter 6, We predict a transition from the bulk planar structure to a novel chain-type thin film accompanied by substantial changes to the electronic structure for a SrCuO2 film thinner than five unit cells thick. In chapter 7, We have used first-principles calculations to determine a magnetic phase diagram of La[O1−x Fx]FeAs as a function of the doping δ, the FeAs in-plane lattice constant a, and the distance d between the Fe and As planes. In chapter 8, We propose an explanation for the spin Seebeck effect in terms of the magnetization potential associated with the thermally induced magnetization gradient, which has so far been neglected.
|Qualification||Doctor of Philosophy|
|Award date||12 Oct 2011|
|Place of Publication||Enschede|
|Publication status||Published - 12 Oct 2011|