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Title: The defect structure and magnetic ground state of ytterbium titanate
Author: Bowman, David
ISNI:       0000 0004 8500 2127
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2018
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The pyrochlore lattice is ideally suited to the exploration of geometrical frustration in three dimensions, and provide the first context in which to study emergent magnetic monopoles. For the quantum analogue of this system, Yb2Ti2O7, whether the magnetic ground state assumes a quantum spin ice state or a Higgs transition to a ferromagnetic phase appears to be sample dependent. Here the defect structure of Yb2Ti2O7 has been characterised and understood using single crystal diffuse scattering obtained on SXD along with balls and springs Monte Carlo modelling. The results show diffuse scattering different to that of other pyrochlores like Y2Ti2O7. In both stuffed and oxygen depleted samples vacancies are appear to be present on the 48f oxygen sites. Annealing was found to eliminate the structural diffuse scattering in an as-grown sample indicating the dominant role of isolated oxygen vacancies. The magnetism of the Yb2Ti2O7 samples was determined using polarised diffuse neutron scattering on D7. The as-grown sample exhibits the magnetic diffuse scattering features observed in previous measurements of Yb2Ti2O7 while annealing in oxygen gives a ferromagnetic ground state. Hence, the true ground state of stoichiometric Yb2Ti2O7 is ferromagnetic and analysis of the peak intensities compared to the existing literature found that ferromagnetism to be all-in all-out. The diffuse scattering observed in the as-grown sample persists in a heavily oxygen depleted sample while stuffing shows suppression of the correlations from the Coulomb phase.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available