Structural and magnetic properties of erbium thin films and Er/Y superlattices
Borchers, Julie Ann
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https://hdl.handle.net/2142/25203
Description
Title
Structural and magnetic properties of erbium thin films and Er/Y superlattices
Author(s)
Borchers, Julie Ann
Issue Date
1990
Doctoral Committee Chair(s)
Salamon, Myron B.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
crystalline erbium thin films
Er/Y superlattices
Molecular Beam Epitaxy
interfacial strain
Language
en
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 interuption 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 14000A 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 erbium 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 ! 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."
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