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|Title:||Heavy rare earth superlattices: Epitaxial growth, structure, and magnetic properties|
|Doctoral Committee Chair(s):||Flynn, C.P.|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||Single crystal superlattices of heavy rare earth metals with yttrium have been synthesized by methods of molecular beam epitaxy developed in this thesis research. Studies of the growth behavior of hcp rare earth metals on bcc transition metal (110) and (211) surfaces, using electron and x-ray scattering probes, are presented. The structural and magnetic properties of Dy-Y and Er-Y superlattices oriented on the (0002) axis are also characterized using x-ray diffraction analysis, bulk magnetization measurement and elastic neutron scattering method.
Epitaxial growth properties of rare earth metals on bcc metal surfaces are anisotropic. Layer-by-layer growth mode is observed for rare earth (0002) planes grown on bcc (110) surfaces. An epitaxial relationship of the Nishiyama-Wasserman type is confirmed for this orientation. Rare earth (1012) planes can be grown tilted on (211) planes of bcc metals. The interface so formed is an asymmetrical coherent tilt boundary. The tilt angles can be predicted by a geometrical model based on the requirement of interfacial coherence with zero long-range strain. One-dimensional pseudomorphism at monolayer coverage, and subsequent dislocation gliding, with a resulting break of surface symmetry for rare earth layers, are also identified. The surface structure of the rare earth (1012) layer is found to be temperature dependent; within a growth temperature window the surface possesses a coherent double-atomic-step structure. Applications of the spontaneous tilt in the synthesis of new magnetic structures including tilted superlattices and atomic chains, are discussed.
Long-range magnetic order is observed in Dy-Y and Er-Y superlattices, and is explained in terms of the RKKY exchange mechanism. The primary differences between the magnetic behavior of superlattices and their constituent magnetic components are that ferromagnetic transitions at low temperature are suppressed. This change is caused by lattice "clamping" to the substrate, which modifies the available magnetoelastic energy and hence also the magnetic phase diagram.
|Rights Information:||Copyright 1990 Du, Rui-rui|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9026172|