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|Title:||Structural and magnetic properties of erbium thin films and erbium/yttrium superlattices|
|Author(s):||Borchers, Julie Ann|
|Doctoral Committee Chair(s):||Salamon, Myron B.|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||The magnetic and structural properties of crystalline erbium thin films and Er/Y superlattices, grown by Molecular Beam Epitaxy, have been analyzed by x-ray scattering, bulk magnetization measurements and neutron diffraction. By comparing the data for the two systems, the effects of the interfacial strain and the artificial modulation on the magnetic behavior of the Er have been determined. Specifically, the imposed secondary periodicity in the superlattices does not cause an interruption of the modulated Er spin order at the Er/Y interfaces. The CAM and basal plane spiral in these systems are coherent through the nonmagnetic yttrium interlayers.
The primary differences between the magnetic behavior of bulk Er and both the films and superlattices are the absence of the Er ferromagnetic state, the enhancement of the critical fields and the reduction of the Neel temperatures. These effects follow directly from the epitaxial basal plane strain which is measurable in films over 14000 A thick. This strain, along with a "clamping" of the Er thermal expansion to the Y lattice, leads to a reduction of the magnetoelastic energy that drives the ferromagnetic transition. The dependence of the magnetoelastic energy on the epitaxial strain is described by a model which accounts for the elastic coupling of the erbuim lattice to the yttrium.
In addition, the neutron diffraction and bulk magnetization measurements show that the sequence and stability of the c-axis commensurate states in bulk Er are altered in all of the samples considered. In the Er films, anomalies in the magnetization and wavevector data indicate that only the high temperature Er "lock-in" structures are formed. For the superlattices the CAM net moment state with four spins up followed by three spins down is stable over an extended temperature and field range. In addition, a new intermediate spin configuration with a net moment of $1\over2$ the saturation moment develops in the superlattice with the thinnest Er interlayers. Variations in the nature of the Er c-axis modulation can qualitatively be explained by a modification of the relative exchange interaction between nearest-neighbor and next-nearest-neighbor spins in the context of the ANNNI model.
|Rights Information:||Copyright 1990 Borchers, Julie Ann|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9021655|