Magnetic resonance of paramagnetically doped materials

• Main Author: Wilman, James
• Published: University of Nottingham 2017
• Subjects: 621.3815; QC501 Electricity and magnetism
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.706395

Colloidal quantum dots (QDs) allow for the tuning of dopant concentration as well as flexibility in the engineering of the surrounding medium. This thesis explores the use of magnetic resonance techniques and the development of hardware in order to characterize paramagnetically doped materials, in particular Mn-doped PbS colloidal QDs, and assess their potential for applications in quantum technologies such as quantum information processing (QIP). Colloidal PbS:Mn QDs capped with thioglycerol/dithiolglycerol ligands were synthesised in aqueous solution. Methods of tailoring the Mn-Mn and Mn-1H interactions, with the aim of maximizing phase memory times, were investigated. The distance between spins was optimized by initially, overgrowing the QDs with an undoped shell and secondly, by dispersing the QDs in solution. The use of a deuterated solution was found to further reduce the dephasing effects of Mn-1H interactions. This resulted in unprecedentedly long phase memory (TM ~ 8 μs) and spin–lattice relaxation (T1 ~ 10 ms) time constants for Mn2+ ions at T= 4.5 K, and in the observation of electron spin coherence (TM ~ 1 μs) near room temperature. Further improvements to relaxation times, as well as enhanced optical properties useful for the initialization and readout of spin qubits, were also studied by embedding the QDs in photonic crystals. Magnetic resonance techniques combined with paramagnetic Mn-impurities in PbS QDs are used for sensitive probing of the QD surface and environment. We report inequivalent proton spin relaxations of the capping ligands and solvent molecules. We determine the strengths and anisotropies of the Mn-1H spin interactions, and establish Mn-1H distances with ~1 Å sensitivity. These findings demonstrate the potential of magnetically doped QDs as sensitive magnetic nano-probes and the use of electron spins for surface sensing. We explore a means of characterizing mechanisms responsible for the functionality of paramagnetically doped materials. The development of instrumentation to identify and quantify interactions between paramagnetic and ordered magnetic phases is described. A probe was designed and built with a fast response time and with the aim of facilitating fast field jump experiments to identifying interactions between the different magnetic phases by correlating the response of a sample to mw irradiation with its response to a field jump.