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Title: A muon and neutron study of multiferric materials
Author: Lewtas, Heather Joanne
ISNI:       0000 0004 2721 0251
Awarding Body: Oxford University
Current Institution: University of Oxford
Date of Award: 2010
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In this thesis multiferroic materials are investigated through a number of different experimental techniques, particularly p,+SR, neutron scattering and impedance spec- troscopy. The magnetic and dielectric properties of materials, which form multiferroic states through different mechanisms, are explored. Inelastic neutron scattering studies have been made of LuMn03 and LuFe204. Large reciprocal space maps have been made of LuFe204 and an initial spin wave dispersion found. The exchange parameters have been estimated from the data and are shown to support ab initio calculations. The spin wave dispersion of LuMn03 has been mapped throughout the Brillouin zone and the exchange parameters extracted by comparison with a spin-wave model. Com- parisons have then been made with other members of the hexagonal manganite family. The analysis is supported by thermal expansion and magnetization studies. The first experiment on a multiferroic combining the p,+SR technique and applied electric fields was performed as a proof of principle experiment on HoMn03. The effect of the elec- tric field on the magnetism has been detected and calculations performed to try and identify muon stopping sites. The family of rare earth chromites have been studied through magnetization and heat capacity experiments as well as p,+SR. The vary- ing entropy and energy level splitting within the family is examined and the debate as to whether they are multiferroic is addressed. An instrument to study dielectric properties at cryogenic temperatures through impedance spectroscopy was designed and constructed. Multiferroics investigated in this thesis using neutron scattering and p,+SR were then studied with this apparatus to look for coupling between magnetic and ferroelectric order parameters. A dielectric anomaly associated with the magnetic transition temperature was observed in LuFe204 which is evidence of the coupling between the order parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available