Study of stoichiometric and electron doped Europium monoxide thin film.

摘要

In this dissertation, we have successfully prepared the high quality EuO films via pulsed laser deposition (PLD) on different substrates, which opens a new simple route to prepare this interesting material. The magnetic mechanism and properties as well as the electronic band structure have been investigated for different samples.;For stoichiometric EuO, firstly the superexchange coupling within the next nearest neighbors of Eu atoms were studied by growing EuO films on different substrates. We discussed the implication of such results with regard to our understanding of the magnetic coupling between neighboring Eu spins. Resonant photoemission studies give strong support for an antiferromagnetic NNN superexchange coupling hybridization mechanism. Secondly, the study of magnetoelectric coupling at the EuO/BaTiO3 interface will be presented. The magnetic properties of EuO, including the critical exponents, grown on a ferroelectric substrate will be presented. The study illustrates an importance of charge doping in magnetoelectric coupling, which can be modulated by ferroelectric polarization reversal.;The properties of EuO can be tuned much by charge carrier doping. Two common methods for realizing the electron doping were also studied in this dissertation, which are rare earth elements doping and oxygen vacancy doping. We will investigate the magnetization of EuO1-x thin films with different oxygen vacancy concentrations as a function of temperature and applied field. A magnetic polaron model that originates from the exchange coupling between the doped electrons and Eu 4f moments is utilized to account for the ferromagnetic ordering above 69 K. We also describe the evolution of the phases of the magnetic orders as the temperature is varied in EuO1-x. For rare earth elements doping, Gadolinium (Gd) and cerium (Ce) were chosen to be the dopants. There are changes in the texture growth and lattice constant seen with a small amount of rare earth elements in the films. The Curie temperatures are enhanced a lot by Gd and Ce doping. Angular-resolved photoemission spectroscopy reveals electron pockets around the points in Gd-doped and Ce-doped EuO, indicating that the band gap in EuO is indirect.