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| Hauptseite > Publikationsdatenbank > Manipulation of magnetism in iron oxide nanoparticle / BaTiO$_{3}$ composites and low-dimensional iron oxide nanoparticle arrays |
| Hauptseite > Publikationsdatenbank > Manipulation of magnetism in iron oxide nanoparticle / BaTiO$_{3}$ composites and low-dimensional iron oxide nanoparticle arrays |
| Book/Dissertation / PhD Thesis | FZJ-2018-03209 |
2018
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-351-8
Please use a persistent id in citations: http://hdl.handle.net/2128/19698
Abstract: Ferrimagnetic (FiM) iron oxide nanoparticles (NPs) on top of ferroelectric BaTiO$_{3}$(BTO) substrates were prepared and a magnetoelectric coupling (MEC) effect was observed in the heterostructures. Iron oxide NPs first were self-assembled as amonolayer on top of BTO substrates. Grazing incidence small angle x-ray scattering(GISAXS) and scanning electron microscopy (SEM) confirm a close-packed hexagonal order of the NP monolayers. By inserting a Ti layer and further capping with an Au layer, an enhanced MEC effect was observed. Scanning transmission electron microscopy (STEM) provides information about the layer structure of the sample. The magnetization shows sharp magnetization jumps at the phase transition temperatures of the BTO substrate. Electric field manipulation of magnetism was performed using a superconducting quantum interference device (SQUID) setup with an electric field implemented. A butterfly shaped curve of the magnetic moment vs. DC electric field was obtained which is coincident with the piezoelectric response of BTO single crystals which confirms a strain mediated MEC. The magnetoelectric ac susceptibility (MEACS) signal as function of temperature under an AC electric field shows abrupt jumps at the BTO phase transition temperatures. The magnetic depth profiles of NP monolayers at various applied DC electric fields were deduced from polarized neutron reflectivity (PNR) results. Fitting of the data shows that the observed differences in reflectivity curves are caused by the changed structural properties of the substrate and layers as a major factor and the altered magnetism of NP monolayers as a minor factor. Also iron oxide NPs self-assembled on BTO films on Nb doped SrTiO$_{3}$ (Nb doped STO) substrates were prepared. The DC electric field vs. magnetization and MEACS results indicate that there is a MEC between NPs and the BTO film. Interface charge and strain transfer are responsible for the MEC effects. Moreover, NPs self assembled into trench-patterned silicon (Si) substrates were prepared to investigate the magnetic anisotropy and collective magnetic behavior. The magnetization vs. magnetic field shows a large shape-induced magnetic anisotropy effect. After the application of a magnetic saturation field along the trenches, electron holography results show that an overall magnetic ordered state exists in the nanoparticle assemblies. In the direction of the trenches, the NPs exhibit a ferromagnetic (FM) -like ordered state and a small memory effect was observed. Whereas large memory effect was observed perpendicular to the trenches. We conclude that the FM ordered state suppresses a superspin glass state of the dipolarly coupled NP moments. This work opens up viable possibilities for energy-efficient electronic devices fabricated by simple self-assembly techniques.
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