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@PHDTHESIS{Schmitz:565535,
author = {Schmitz, Markus},
othercontributors = {Brückel, Thomas and Juschkin, Larissa},
title = {{S}train and electric field mediated manipulation of
magnetism in
{L}a$_{(1-x)}${S}r$_x${M}n{O}$_3$/{B}a{T}i{O}$_3$
heterostructures},
school = {RWTH Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2015-07869},
pages = {1 Online-Ressource (VI, 141 Seiten) : Illustrationen},
year = {2015},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2016; Dissertation, RWTH Aachen, 2015},
abstract = {Heterostructures of ferromagnetic La$_{1-x}$Sr$_x$MnO$_3$
(LSMO) and ferroelectric BaTiO$_3$ (BTO) were produced and
investigated for their structural and magnetic properties.
The combination of these ferroic properties can lead to an
artificial multiferroic. A possible magneto-electric
coupling at the interface was proposed by Burton et al..
Thus, special emphasis was given to the manipulation of
magnetic properties by applying electric fields. A
magneto-electric coupling could be observed in the
heterostructures under investigation. Epitaxial LSMO thin
films were grown on BTO substrates using a state-of-the-art
oxide molecular beam epitaxy(OMBE) and a high oxygen
sputtering system (HOPSS). Stoichiometric LSMO films with
doping levels of $x=0.5$ and $x=0.3$ were produced. The film
quality in terms of roughness and crystalline structure was
confirmed by X-ray scattering methods. The presence of
structural domains in the BaTiO$_3$ single crystal
substrate, whose proportion could be altered due to the
application of electric fields, was shown by X-ray
diffraction. Tensile strain is induced into the epitaxial
La$_{1-x}$Sr$_x$MnO$_3$ films in the whole temperature range
under investigation. The magnetization of LSMO alteres by
the variation of strain induced into the film, generated by
the different structural phases of single crystal BaTiO$_3$
substrates. The magnetization shows sharp steps at the
structural phase transition temperatures of BTO. The
evaluation of magnetic hysteresis loops reveals a change of
the magnetic anisotropy of LSMO for each structural phase of
BTO, but also within the orthorhombic phase. Special focus
was given to the manipulation of magnetic properties by the
application of electric fields. A newly established
measurement option was used to determine the magnetic
response to an applied electric field as a function of
temperature and magnetic field. The electrically induced
modification of the magnetization is profound near the
structural phase transition temperatures. Electrical
hysteresis loops give a detailed view on the influence of
the electric field on the magnetization. The magnetic
coercivity field shifts by the application of electric
fields giving rise to a change of the magnetic anisotropy.
Polarized neutron reflectivity measurements yield the
magnetization profiles of the LSMO/BTO heterostructures to
clarify a limitation of the effect to the interface. Samples
grown by OMBE indicate a better epitaxial crystal structure
due to a strain induced reduction in the magnetization at
the interface. Samples produced by HOPSS show a reduced
magnetization for higher layer thicknesses, which might be
related to oxygen vacancies. Simulations of the polarized
neutron reflectivity data for different electric field
directions reveal that the observed differences in the
reflectivity are mostly related to altered structural
properties. Several mechanisms, which might be responsible
for the observed effects in LSMO on BTO, are discussed.
Strain effects via the elastic channel can lead to a
rotation of the magnetic anisotropy, a change of the orbital
ordering or the exchange interaction. Also carrier-mediated
effects and oxygen diffusion under applied electric fields
have to be considered. Furthermore, the ferroelectric
properties of the BaTiO$_3$ substrates and their response to
the electric field is of crucial importance to explain the
observed effects.},
cin = {134310 / 130000 / 139420},
ddc = {530},
cid = {$I:(DE-82)134310_20140620$ / $I:(DE-82)130000_20140620$ /
$I:(DE-82)139420_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-rwth-2015-078698},
url = {https://publications.rwth-aachen.de/record/565535},
}
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