Magnetic studies of epitaxial neodymium

The magnetic properties of metallic neodymium (Nd) have been the subject of intense study for the last three decades. Current research into the magnetic properties of compounds containing Nd benefits from a deeper understanding of the elemental properties. Early studies of Nd prepared epitaxially as thin films with either nonmagnetic yttrium (Y) or magnetic praseodymium (Pr) demonstrated magnetic properties hitherto unforeseen. To probe the newly discovered phenomenon, thin films of Nd and NdY alloys have been prepared in one of two orientations: some with the crystallographic c axis perpendicular to the film and some with the crystallographic b axis perpendicular to the film. The films exhibit unexpected structural and magnetic properties. The crystal structures agree with lattice types known to be exhibited by bulk alloys, but epitaxial strain has stabilized these lattices at concentrations different from those observed in the bulk. The b-axis films of elemental Nd exhibit the HCP structure found usually at Y concentrations of 40% and greater. These films demonstrate a density 8% larger than elemental Nd, an astonishing feat for epitaxial films. Several c-axis films exhibit the crystal lattice of elemental samarium, but again at richer Nd concentrations than observed in bulk alloys. The films show magnetic responses that indicate long-range antiferromagnetic ordering occurs at temperatures 50% greater than ordering temperatures of elemental Nd. The nature of the antiferromagnetic state has been studied with magnetic neutron scattering and magnetic x-ray scattering. No evidence of the ordered magnetic structure of elemental Nd has been found. A c-axis alloy film of Nd andY in the samarium lattice structure exhibits helical ordering as found for c-axis superlattices of Nd andY. The period of modulation is independent of temperature and commensurate with the crystal lattice. Consideration is given to the possible mechanisms which account for the observed behavior of the films and are consistent with present understanding of the magnetic ordering of epitaxial films and bulk crystals. The changing symmetries of the lattice, epitaxial strain, and deduced changes in the electronic structure of the metal are offered as the most likely explanation of the results obtained.U of I OnlyThesi