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Title: Spin-wave measurements of sodium cobaltate and linarite using inelastic neutron scattering
Author: Cemal, Eron
ISNI:       0000 0004 8499 3053
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2016
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In this thesis work, the magnetic excitations of two different materials, NaxCoO2 and linarite (PbCuSO4(OH)2) have been explored using inelastic neutron scattering. The study of these materials improves our understanding of quantum theory and paves the way for new technologies. In NaxCoO2, for certain values of x, long-ranged Na-vacancy superstructures can occur. It has been shown that these superstructures have anharmonic lattice vibration modes which drastically reduces thermal transport in NaxCoO2. It is believed that the superstructures have an effect on the magnetism as well; however, this has not been proven so far. In this thesis work, the spin-wave spectrum is measured for two different superstructures. An anomalous magnetic waterfall effect is observed in the spin-wave dispersion for one sample which is interpreted as magnon-phonon coupling. Linarite (PbCuSO4(OH)2) is a naturally occurring mineral. At low temperatures, it creates a quasi low-dimensional system which is of theoretical interest. Such a system has very strong magnetic interactions along one particular direction, but rather weak interactions along other directions. Based on some physical-properties measurements, it has been suggested that linarite could sustain an exotic new quantum phase. In this novel phase it is suggested the spins do not have any transverse long range order but instead they have quasi-long-range spin-multipolar order. In this thesis work, the measured magnetic excitations indicate that linarite could be in the correct parameter region for displaying the novel quantum phase. Diffraction experiments were carried out to try and find direct experimental evidence of the suggested spin-multipolar phase. Additionally, the rich magnetic phase diagram of linarite was explored by various magnetisation and diffraction experiments.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: NAXCOO2 ; Linarite ; PbCuSO4(OH)2) ; Neutron Scattering ; Spin-waves ; INELASTIC NEUTRON-SCATTERING ; Na0.8CoO2 ; Magnetism ; magnon waterfall