A synchrotron radiation study of the epitaxial growth of rare earth metal overlayers and their magnetic properties.
thesisposted on 19.11.2015, 09:17 by Stuart Neil. Mozley
The structural and magnetic properties of rare earth metal overlayers have been investigated using techniques utilising synchrotron radiation. The magnetic ordering in ultrathin Tb layers was studied using Spin Polarized Photoelectron Diffraction. Magnetic information is obtained from the variation with temperature of the relative intensity of the peaks in the Tb 4s multiplet splitting. Short range magnetic order is shown to exist in the ultrathin Tb film up to temperatures significantly higher than the bulk transition temperature. The growth mode of Gd films on Mo(110) was investigated using Surface X-ray Diffraction. The formation of the Gd adlayer was found to change with substrate temperature. At room temperature the growth mode was Stranski-Krastanov, but at higher temperatures, the growth proceeds by step-flow and the reflected X-ray intensity decays. The growth curve is parabolic at the start of deposition up to 1monolayer before becoming a constant value for the duration of the deposition. The epitaxial growth was found to improve if the substrate was first exposed to a controlled dosage of oxygen gas. Oscillations in the reflected X-ray intensity were observed up to a coverage of 7 monolayer. It is proposed that oxide clusters form on the surface and act as nucleation sites which facilitate epitaxial growth. The magnetic properties of ultrathin Gd films have been studied using Circular Magnetic X-ray Dichroism. To induce magnetisation in the Gd film, a buffer layer of Fe was deposited on to the Mo(110) substrate prior to deposition of the Gd film. Sum rules were used to calculate the expectation value of the orbital angular momentum operator, (Lz), which was found to increase as the thickness of the Fe buffer layer was increased.