Magnetoelectric interactions in multiferroic thin-film heterosystems and nanostructures

Electric-write magnetic-read memory-based devices replace conventional hard-disk drives, since they offer an advantage of reduced power consumption for writing. The next generation spintronic application building blocks are multiferroic materials, which combine and couple magnetic and electric properties. It was therefore of great importance to investigate the still unexplored phenomena, such as electronic structure changes at the interfaces of these heterosystems. Within the scope of this thesis, we have attempted to develop artificial multiferroic (AM) materials with desired ferroic properties. We studied two model systems: (i) BaTiO${}_3$/La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$/SrTiO${}_3$ (BTO/LSMO/STO) and (ii) Fe/BaTiO${}_3$ (Fe/BTO). Firstly, epitaxially grown BTO and LSMO films on STO grown by the pulsed laser deposition (PLD) technique were investigated. Magnetic properties, surface morphologies, and crystal phases of the as-received samples were characterized. To study charge anisotropy and coupling of two ferroic orders of the AM heterostructures element specifically we performed X-ray absorption spectroscopy (XAS) measurements with polarized X-rays at UE56/1 - SGM FZ Jülich Beamline at BESSY-II synchrotron facility. Secondly, the Fe/BTO system is investigated using a cutting-edge spectromicroscopic tool, namely the low energy electron microscope/X-ray photoelectron emission microscope (LEEM/XPEEM) located at the same end station at BESSY-II. LEEM, Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) were used to study the ferroelectric domains, cleanness and termination of the BTO(001) surface, respectively. Spatially resolved electronic structure of ferroelectric domains were demonstrated for the first time using X-ray linear dichroism (XLD)-PEEM contrast mechanism. In-situ and ex-situ Fe growth by e-beam evaporation on BTO(001) was established. To present the interplay between ferroelectricity and inverse magnetostrictive behavior in Fe/BTO, X-ray magnetic circular dichroism (XMCD)- and XLD-PEEM experiments were conducted.