Pulsed laser deposited VO2 and Co-Zn-Mn thin films toward novel functionalities

The central aim of this thesis work was to grow high-quality VO2 and helimagnetic thin films and to study and optimize their structures and properties, to help build better functional devices in the future. For growth pulsed laser deposition (PLD) was used, which is widely accepted for growth of functional oxide materials. VO2 was chosen due to its rich metal-to-insulator phase transition which is still not fully understood after many decades of research, and because of the potential diverse applications of VO2 thin films. These films were grown on sapphire and TiO2 substrates under comparable conditions, and the large differences in the macro-scale electrical transition characteristics could be linked to the differences in (atomic) structures as studied using scanning transmission electron microscopy (STEM). The intermediate VO2-M2 phase was also stabilized using strain engineering on TiO2(001) substrate and confirmed using extensive STEM image analysis. This can be used to build devices to access functionalities like multi-level resistive switching. We also aimed to extend the PLD growth technique to the fabrication of non-oxide films. This had been done before in the research group with chalcogenide-based films which act as phase-change materials. β-Mn phase Co-Zn-Mn was chosen as the second system, since it can exhibit complex magnetic textures like skyrmions below the transition temperature, and thus is a potential candidate for spintronics-based devices. In this work, the growth parameters of Co8Zn8Mn4 films were optimized, and the resulting films have very low oxidation and exhibit magnetic properties comparable to those of the bulk phase.