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https://hdl.handle.net/2142/31296
Description
Title
Magnetic studies of epitaxial neodymium
Author(s)
O'Donovan, Kevin Vincent
Issue Date
2000
Doctoral Committee Chair(s)
Salamon, Myron B.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
metallic neodymium
thin films
yttrium (Y)
praseodymium (Pr)
Language
en
Abstract
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.
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