Interface phenomena in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$/La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ heterostructures and a quest for p-electron magnetism

Waschk, Markus

Book/Dissertation / PhD Thesis

FZJ-2017-03847

Interface phenomena in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$/La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ heterostructures and a quest for p-electron magnetism

Waschk, M. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-281-8

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies 157, IX, 205 S. (2017) = RWTH Aache, Diss., 2017

Please use a persistent id in citations: http://hdl.handle.net/2128/15911

Abstract: Transition metal oxides (TMO's) show functionalities which make them promising candidates for sensors and storage devices in future information technologies, because of electronic correlations and complex ordering phenomena. Such devices will consist of heterostructures of different TMO's, where interfaces can add additional functionalities, which cannot be found in the individual constituents. The subtle balance between electronic, spin, and lattice degrees of freedom leads to a variety of quantum phenomena in TMO's and results in an extreme sensitivity to external stimuli such as pressure and magnetic fields. The use of thin films increases the plethora of phenomena due to the reduced dimensionality, and epitaxial strain. At the interface completely new phenomena like magnetic interlayers between two non-magnetic layers or metallic behavior between two insulating materials may emerge, which cannot be found in the bulk materials. The main part of this thesis is an investigation of the system La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ (LSFO) and La$_{2/3}$Sr$_{1/3}$MnO$_{3}$(LSMO). LSFO contains a Verwey transition with a resistivity increase of eight orders of magnitude from 300K to 10 K, coinciding with an antiferromagnetic and a charge ordering transition. The samples were prepared with two powerful oxide growth methods, the high oxygen pressure sputtering, which was used for the LSMO growth, and a state of the art oxide molecular beam epitaxy system for the LSFO growth. The optimized growth of the individual layers and the heterostructures will be presented in detail. Furthermore, a detailed investigation with regard to structural, magnetic, and electronic properties will be shown. Single layers as well as heterostructures grow epitaxially on a SrTiO$_{3}$ substrate, in spite of a transfer procedure from one preparation chamber to another under atmosphere, which was necessary for the growth of heterostructures. The stoichiometric samples exhibit a good crystallinity and low surface roughness. However, the interface morphology in the heterostructures depends crucially on the growth order. Significant iron interdiffusion from the pre-deposited LSFO into the LSMO layer to at least nine unit cells is observable for the system LSMO/LSFO, whereas the LSFO deposited on LSMO exhibits a sharp interface with interdiffusion restricted to two unit cells at most. The differences of the magnetic properties are also remarkable. The LSMO/LSFO sample shows an increased Curie temperature, a reduced interface magnetization, and a vanishing exchange bias effect, which is linked to the interdiffusion. In contrast, the system LSFO/LSMO has a homogeneous magnetization in the whole layer, but the macroscopic magnetization measurements reveal an additional magnetic impurity phase which persists at temperatures higher than 380 K, with a rather high coercive field. M(H) measurements feature an inverted hysteresis at 110K and a strong field cooling dependency of the magnetization at 10 K, which includes a significant exchange bias effect. The second investigated system belongs to a new class of magnetic materials, namely those where magnetism is caused by p-electrons as predicted by Gruber et al. [1] and Oja et al. [2]. These materials provide new routes to future storage devices as one can magnetically dope ferroelectric materials like BaTiO3 to achieve artificial multiferroic materials. The realization of such systems seems to be challenging and only initial results of a BaTiO$_{3}$ bulk system and KTaO$_{3}$/SrTiO$_{3}$ heterostructure can be presented.

Note: RWTH Aache, Diss., 2017

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