Multiferroicity in oxide thin films and heterostructures

Glavic, Artur

Book	PreJuSER-22239

Multiferroicity in oxide thin films and heterostructures

Glavic, A. (Corresponding author)FZJ*

2012
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-803-7

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Schlüsseltechnologien / Key Technologies 45, III, 152 S. (2012)

Please use a persistent id in citations: http://hdl.handle.net/2128/4607

Abstract: In this work a variety of different systems of transition metal oxides ABO$_{3}$ (perovskite materials, where B stands for a transition metal and A for a rare earth element) were produced as thin films and heterostructures and analyzed for the structural, magnetic and ferroelectric properties. For the epitaxial film preparation mostly pules laser deposition (PLD) was applied. For one series high pressure oxide sputter deposition was used as well. The bulk multiferroics TbMnO$_{3}$ and DyMnO$_{3}$, which develop their electric polarization due to a cycloidal magnetic order, have been prepared as single layers with thicknesses between 2 and 200 nm on YAlO$_{3}$ substrates using PLD and sputter deposition. The structural characterization of the surfaces and crystal structure where performed using x-ray reflectometry and diffraction, respectively. These yielded low surface roughness and good epitaxial growth. The magnetic behavior was macroscopically measured with SQUID magnetometry and microscopically with polarized neutron diffraction and resonant magnetic x-ray scattering. While all investigated samples showed antiferromagnetic order, comparable with the collinear magnetic phase of their bulk materials, only the sputter deposited samples exhibited the multiferroic low temperature cycloidal order. The investigation of the optical second harmonic generation in a TbMnO$_{3}$ sample could proof the presence of a ferroelectric order in the low temperature phase. The respective transition temperatures of the thin films have been very similar to those of the bulk materials. In contrast an increase in the rare earth ordering temperature has been observed, which reduces the Mn order slightly, an effect not known from bulk TbMnO$_{3}$ crystals. The coupling of the antiferromagnetic order in TbMnO$_{3}$ to ferromagnetic layers of LaCoO$_{3}$ was investigated in super-lattices containing 20 bilayers produced with PLD on the same substrates. The SQUID magnetometry yielded a strong influence of the antiferromagnetic transitions on the overall magnetization. Element specific magnetization measurement from XMCD showed that the ferromagnetism has only Co contributions. The analysis of a polarized neutron diffraction experiment resulted in a complex magnetic model, which requires a strong coupling of the magnetic moments of Mn and Co. The investigation of a system build of EuTiO$_{3}$-BaTiO$_{3}$ super-lattices, produced with PLD on GdScO$_{3}$ substrates, for a magnetic order of the Eu system with polarized neutron reflectometry could eliminate ferromagnetism down to 0.01 $\mu_{B}$. Nevertheless, the system could be used to test simulation models, build for reflectivity and diffraction on the other systems. All simulations showed very good agreement with the experiments. In the context of this thesis and in addition to the already mentioned simulations the evaluation software Plot.py was developed, which was used for most of the data analysis.

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