Mapping Nanoscale Metal-Insulator Phase Transition in NdNiO3 and Molecular Beam Epitaxy of SmTiO3 Thin Films

Abstract

The subject of this thesis is the growth and characterization of quantum materials. Quantum materials are those in which correlated electron interactions result in functional emergent properties like high-temperature superconductivity, colossal magnetoresistance, ferromagnetism, and metal-insulator transitions. 3d transition metal oxides, particularly perovskites, have been found to be a fertile area of investigation in quantum materials. Rare earth nickelates and titanates fall into this category and are examined here. The bulk of this work concerns soft x-ray spectroscopy and imaging of a free-standing NdNiO3 thin film. NdNiO3 displays a metal-insulator transition as well as a magnetic transition, with the respective Curie and Néel temperatures coinciding. We employ x-ray absorption spectroscopy to characterize the electronic transition from metallic to insulating on cooling the sample, noting the magnitude of the hysteresis in the process; x-ray magnetic scattering to characterize the magnetic transition on heating; and scanning transmission x-ray spectromicroscopy to search for the formation of distinct domains of metallic and insulating phases during the progress of the electronic phase transition. Although these electronic domains were not observed, the sum of our experiments present confirmation that freestanding films of this novel configuration possess similar magnetic and electronic properties to those observed in their bulk counterparts. This finding is significant as it indicates that films of this type could be integrated into device applications in the same manner as bulk nickelates. A secondary thrust of this work is the development of the capability to synthesize thin films by molecular beam epitaxy (MBE) at the Canadian Light Source for future studies of quantum materials with an emphasis on interface effects and heterostructures. We briefly present results of an effort to grow SmTiO3 thin films by MBE with characterization by electron diffraction and spectroscopy.