Two-dimensional and three-dimensional magnetism in ultrathin epitaxial rare-earth metal films
Park, Byeongju
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https://hdl.handle.net/2142/19635
Description
Title
Two-dimensional and three-dimensional magnetism in ultrathin epitaxial rare-earth metal films
Author(s)
Park, Byeongju
Issue Date
1995
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Engineering, Materials Science
Language
eng
Abstract
This thesis reports the investigation of the magnetic behavior of ultrathin epitaxial films of the heavy rare-earth elements; Gd, Er, and Dy, grown with the technique of Molecular Beam Epitaxy (MBE). By employing advanced film fabrication techniques, each magnetic rare-earth element layer, between 0.1 and 10 atomic layers thick and magnetically separated from one another by thick spacers, is grown in layer-by-layer growth mode to insure high crystal quality. Magnetization of the resulting films is measured to identify the spin structures and the magnetic phases. The localized 4f spins in the rare-earth layers and complete interlayer magnetic separation give the present approach a unique advantage over the previously used experimental methods.
Expounding on the capability to fabricate two-dimensional systems, this thesis explores the following questions. How do these systems behave in two dimension? At what thickness does the transition between the two-dimensional behavior and the three-dimensional behavior occur? What are the effects of exchange anisotropy caused by the anisotropic 4f electrons and the crystal field? What are the effects of the basal plane strain caused by lattice mismatch between spacer layers and magnetic elements?
The answers can be summarized as follows. All the systems probed in this thesis display spin-glass phases in two dimension. Dimensional crossover occurs between 1-3 monolayer thickness in these films. The effect of the exchange anisotropy is reflected in the magnitude of the susceptibility along different axes. Strain, or lattice mismatch, introduces random anisotropy into the systems in the ultrathin films resulting in random axis magnet phases. The overall picture is a complex interplay of the exchange anisotropy of the magnetic element, the random anisotropy caused by the size difference between the spacer elements and the magnetic elements, randomness in exchange interaction due to the structural randomness, basal plane strain due to the spacer layer, and dimensional crossover as a function of the film thickness.
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