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Electronic and spin control in functional oxide heterostructures

DOI: 10.17877/DE290R-22350 DOI Help

Authors: Ronja Anika Hinz (Technischen Universit├Ąt Dortmund)
Co-authored by industrial partner: No

Type: Thesis

State: Published (Approved)
Published: August 2021

Abstract: Transition metal oxides exhibit a variety of physical properties due to their high tunability of spin, orbital, and charge degrees of freedom. This thesis studies two complex, transition metal oxide thin film/substrate systems, the NiFe2O4/Nb:SrTiO3 (NFO/STO) and the La0.3Sr0.7MnO3/Nb:SrTiO3 (LSMO/ STO). NFO is a ferrimagnetic insulator. LSMO is a ferromagnetic half metal and below a critical thickness transitions to an insulator. However, the physical properties of those complex oxides heterostructures are often directly linked to the quality of the thin oxide film and the interactions between the oxide thin film and its substrate at the interface. In this thesis the ultra thin NFO film growth via pulsed laser deposition is optimized. First those optimized, smooth and single crystalline NFO films are studied with lab measurement methods to ensure a high film quality. In a next step their stoichiometry and crystalline occupancy is studied via hard X-ray photoemission (HAXPES) and X-ray absorption spectroscopy, which were recorded at the large scale synchrotron BESSY II, PETRA III and the DIAMOND Light source. The stoichiometry and occupancy is found to match the theoretical expectations of the NFO oxide in the inverse spinel structure. The magnetic response of the NFO/STO heterostructure is researched with the element selective X-ray magnetic circular dichroism (XMCD). Due to the proximity effect the Ti signal mimics the ferrimagnetic response of the NFO thin film. The electronic properties of Au/NFO/STO and Pt/LSMO/STO devices were investigated via in-operando HAXPES measurements. In-operando HAXPES is recording HAXPES spectra during a voltage is applied to the sample. The band alignment and band bending are investigated by applying Kraut' s method to the HAXPES spectra.

Diamond Keywords: Ferromagnetism

Subject Areas: Materials, Physics

Instruments: I10-Beamline for Advanced Dichroism

Other Facilities: BESSY II; PETRA III

Added On: 25/08/2021 09:16

Discipline Tags:

Materials Science Quantum Materials Physics Hard condensed matter - structures Magnetism Surfaces interfaces and thin films

Technical Tags:

Spectroscopy X-ray Photoelectron Spectroscopy (XPS) Hard X-ray Photoelectron Spectroscopy (HAXPES)