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University of New South Wales
1.
Kareri, Yousef.
Investigation of Spin and Charge Order in Ferrite Spinels by Synchrotron X-ray and Neutron Diffraction.
Degree: Physics, 2020, University of New South Wales
URL: http://handle.unsw.edu.au/1959.4/65544 
;
https://unsworks.unsw.edu.au/fapi/datastream/unsworks:64720/SOURCE02?view=true
► Strongly correlated electron systems such as transition metal oxides host a complex interplay between electron spin, charge and orbital degrees of freedom. Hence, the electronic…
(more)
▼ Strongly correlated electron systems such as transition metal oxides host a complex interplay between electron spin, charge and orbital degrees of freedom. Hence, the electronic interactions taking place in these materials challenge our understanding of their underlying mechanisms and offer an immense opportunity for fundamental and applied research. The competing interactions can induce exotic phenomena such as charge-ordered phases, metal-to-insulator transitions, magnetic phase transitions, colossal magnetoresistance, multiferroicity and even high-temperature superconductivity. Among these materials, we highlight Fe3O4 as the oldest known magnet, which undergoes a metal-to-insulator transition: the Verwey transition at 120K. In 1939, Verwey explained this transition by proposing an ordering of the charges of the Fe2+ and Fe3+ ions. However, due to the complexity of the structure of magnetite its crystallographic details and therefore, the precise charge ordering pattern remains debated. The novel approach in this thesis is to trace the evolution of the Verwey transition in Fe3O4 upon Cu-doping through high-resolution neutron and synchrotron X-Rays diffraction experiments. The other end member, CuFe2O4 possesses a tetragonal crystal structure with a perfectly collinear ferrimagnetic order and a TC of 790 K. Its 2-dimensional layered counterpart CuFe2O4 has attracted considerable attention due to its magnetic spin cycloidal structure and its multiferroic properties. We did, therefore, raise the question: can we induce a spin canting and finally a cycloidal spin structure which could be the basis for a multiferroic ground state by Zn-doping in CuFe2O4. The end member of this doping series, ZnFe2O4 displays a 3-dimensional geometrically frustrated magnetic structure with short-range antiferromagnetic order. Although, ZnFe2O4 can be considered as an antiferromagnet with an N'eel temperature of 10K, its magnetic interactions are more complex since spin frustration occurs between the antiferromagnetically coupled third-neighbour spins rather than between the ferromagnetically coupled first-neighbour spins. In this thesis, high-resolution synchrotron X-ray and neutron powder diffraction experiment in combination with magnetisation measurements were performed on powder and single crystal samples of Cu-doped Fe3O4, Zn-doped CuFe2O4 and pure ZnFe2O4 in order to understand the underlying mechanisms in this class of spinel materials.
Advisors/Committee Members: Ulrich , Clemens , Physics, Faculty of Science, UNSW.
Subjects/Keywords: Numbers {2,3,4 and C}-subcript below; ,and {+2}, {+3}-subcript up
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APA (6th Edition):
Kareri, Y. (2020). Investigation of Spin and Charge Order in Ferrite Spinels by Synchrotron X-ray and Neutron Diffraction. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/65544 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:64720/SOURCE02?view=true
Chicago Manual of Style (16th Edition):
Kareri, Yousef. “Investigation of Spin and Charge Order in Ferrite Spinels by Synchrotron X-ray and Neutron Diffraction.” 2020. Doctoral Dissertation, University of New South Wales. Accessed January 24, 2021.
http://handle.unsw.edu.au/1959.4/65544 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:64720/SOURCE02?view=true.
MLA Handbook (7th Edition):
Kareri, Yousef. “Investigation of Spin and Charge Order in Ferrite Spinels by Synchrotron X-ray and Neutron Diffraction.” 2020. Web. 24 Jan 2021.
Vancouver:
Kareri Y. Investigation of Spin and Charge Order in Ferrite Spinels by Synchrotron X-ray and Neutron Diffraction. [Internet] [Doctoral dissertation]. University of New South Wales; 2020. [cited 2021 Jan 24].
Available from: http://handle.unsw.edu.au/1959.4/65544 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:64720/SOURCE02?view=true.
Council of Science Editors:
Kareri Y. Investigation of Spin and Charge Order in Ferrite Spinels by Synchrotron X-ray and Neutron Diffraction. [Doctoral Dissertation]. University of New South Wales; 2020. Available from: http://handle.unsw.edu.au/1959.4/65544 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:64720/SOURCE02?view=true
University of New South Wales
2.
Graham, Paul.
Magnetic, ferroelectric and structural phenomena in rare earth manganite and ferrite systems: Raman spectroscopy and neutron diffraction studies.
Degree: Physics, 2016, University of New South Wales
URL: http://handle.unsw.edu.au/1959.4/57141
;
https://unsworks.unsw.edu.au/fapi/datastream/unsworks:42677/SOURCE02?view=true
► The discovery of emergent phenomena arising from the interplay between magnetism, ferroelectricity and structure in multiferroic materials provides a myriad of potential capabilities in future…
(more)
▼ The discovery of emergent phenomena arising from the interplay between magnetism, ferroelectricity and structure in multiferroic materials provides a myriad of potential capabilities in future solid state technologies. Despite extensive investigations in this field, many unsolved issues surround magnetoelectric coupling in several multiferroic systems, and in many cases there are competing approaches that attempt to describe their underlying mechanisms. Collectively, the projects in this thesis represent a two-pronged approach that utilises the complementary techniques of Raman light scattering and neutron diffraction as a means to investigate the contentious role of crystal structure in magnetoelectric coupling for the type-II multiferroic RMnO3 (R = Tb, Dy) and RMn2O5 systems (R = Tb, Ho, Y), and furthermore in potentially-multiferroic ErFeO3.The isotopic substitution of oxygen-18 significantly modifies the lattice dynamics of transition-metal oxide systems. In many materials, this can result in isotope-induced shifts in magnetic, ferroelectric, or superconducting phase transition temperatures that provide
new understanding into the underlying physical processes that define their properties. Remarkably, oxygen-isotope substitution in RMnO3 (R = Tb, Dy) systems does not alter the onset of the multiferroic regime, indicating that magnetoelectric coupling is primarily a magnetically-driven phenomenon within these compounds. The combination of Raman scattering and neutron diffraction techniques allowed several key insights to be obtained. For both RMnO3 and RMn2O5 systems, Raman spectroscopy revealed that magnetically-driven ferroelectricity imposes significant effects that alter mode energies and lifetimes which indicate displacement-induced ferroelectricity. Furthermore, we observe remarkable structural behaviours in the form of altered bond lengths or faint Bragg reflections that indicate the existence of symmetry breaking. Our Raman study on ErFeO3 presents evidence of broken symmetry hitherto unobserved, as well as the interplay between magnetism and structure from strong interactions between different magnetic sublattices. Our combined approach provides crucial answers in understanding the emergent phenomena derived from the complex interplay between magnetic, ferroelectric and structural properties within these materials.
Advisors/Committee Members: Ulrich, Clemens, Physics, Faculty of Science, UNSW.
Subjects/Keywords: Ferroelectricity; Multiferroics; Magnetism; Raman Spectroscopy; Neutron Diffraction
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APA (6th Edition):
Graham, P. (2016). Magnetic, ferroelectric and structural phenomena in rare earth manganite and ferrite systems: Raman spectroscopy and neutron diffraction studies. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/57141 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:42677/SOURCE02?view=true
Chicago Manual of Style (16th Edition):
Graham, Paul. “Magnetic, ferroelectric and structural phenomena in rare earth manganite and ferrite systems: Raman spectroscopy and neutron diffraction studies.” 2016. Doctoral Dissertation, University of New South Wales. Accessed January 24, 2021.
http://handle.unsw.edu.au/1959.4/57141 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:42677/SOURCE02?view=true.
MLA Handbook (7th Edition):
Graham, Paul. “Magnetic, ferroelectric and structural phenomena in rare earth manganite and ferrite systems: Raman spectroscopy and neutron diffraction studies.” 2016. Web. 24 Jan 2021.
Vancouver:
Graham P. Magnetic, ferroelectric and structural phenomena in rare earth manganite and ferrite systems: Raman spectroscopy and neutron diffraction studies. [Internet] [Doctoral dissertation]. University of New South Wales; 2016. [cited 2021 Jan 24].
Available from: http://handle.unsw.edu.au/1959.4/57141 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:42677/SOURCE02?view=true.
Council of Science Editors:
Graham P. Magnetic, ferroelectric and structural phenomena in rare earth manganite and ferrite systems: Raman spectroscopy and neutron diffraction studies. [Doctoral Dissertation]. University of New South Wales; 2016. Available from: http://handle.unsw.edu.au/1959.4/57141 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:42677/SOURCE02?view=true
University of New South Wales
3.
Chang, Fenfen.
Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels.
Degree: Physics, 2017, University of New South Wales
URL: http://handle.unsw.edu.au/1959.4/57563
;
https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true
► Multiferroics exhibit tremendous potential in technological applications, of which the interplaybetween the ferro-/antiferromagnetic, ferroelectricity, and ferroelasticity can be manipulatedby external parameters such as electric or…
(more)
▼ Multiferroics exhibit tremendous potential in technological applications, of which the interplaybetween the ferro-/antiferromagnetic, ferroelectricity, and ferroelasticity can be manipulatedby external parameters such as electric or magnetic fields and even can be created byproper control of internal parameters, such as oxygen-content, cation doping, and internalpressure. Invaluable insight into the multiferroicity can be provided by investigating the roleof such parameters in the crystallographic and magnetic structures of transition metal oxides.In this thesis, a comprehensive studies of contribution of oxygen-deficiencies and cation dopingto the various phases are presented, which utilize the neutron and synchrotron powderdiffraction.The multivalent nature of cobalt ions in SrCoO3d causes an oxygen-content dependentphase diagram. It is vital to determine the precise crystallographic and magnetic structure ofoxygen-vacancy ordered SrCoO3d , which provides prerequisite to reveal the mechanism ofits multiferroicity in the corresponding thin film samples. Using the neutron and synchrotronpowder diffraction techniques, the correct space group and precise magnetic structures aredetermined for the different oxygen-vacancy ordered phases: the brownmillerite SrCoO2:5,the tetragonal SrCoO2:875, and the cubic SrCoO3.Ferroelectricity can be induced by the canted spin configuration, which exists widely inthe frustrated spin systems. With such an expectation, Zn-substituted CuFe2O4 was studiedand a comprehensive phase diagram was built for Cu1xZnxFe2O4. Spin canting couldlead to a spin spiral phase which could possibly induce a multiferroic state as observed inCuFeO2. The purpose of this project was to further investigate the spin canting in ZndopedCuFe2O4 and elucidate the possibility of multiferroicity in this system. Furthermore,pure ZnFe2O4 is already an interesting highly frustrated spin system. Magnetite is the oldestknown magnet. As the first known multiferroics, the ferroelectricity in Fe3O4 is drivenby the Verwey transition. However, the microscopic origin of the Verwey transition in Fe3O4is still in debate. In order to obtain a deeper insight into the mechanism of the charge ordering,Cu-doped Fe3O4 was investigated using the high-resolution neutron and synchrotrondiffraction. The main emphasis was the stability of the Verwey transition with charge carrierdoping.
Advisors/Committee Members: Ulrich, Clemens, Physics, Faculty of Science, UNSW, Sushkov, Oleg, Physics, Faculty of Science, UNSW.
Subjects/Keywords: Oxygen vacancy ordering; Neutron diffraction; Synchrotron powder diffraction; Verwey transition; Charge ordering
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APA (6th Edition):
Chang, F. (2017). Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true
Chicago Manual of Style (16th Edition):
Chang, Fenfen. “Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels.” 2017. Doctoral Dissertation, University of New South Wales. Accessed January 24, 2021.
http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true.
MLA Handbook (7th Edition):
Chang, Fenfen. “Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels.” 2017. Web. 24 Jan 2021.
Vancouver:
Chang F. Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels. [Internet] [Doctoral dissertation]. University of New South Wales; 2017. [cited 2021 Jan 24].
Available from: http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true.
Council of Science Editors:
Chang F. Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels. [Doctoral Dissertation]. University of New South Wales; 2017. Available from: http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true
University of New South Wales
4.
Reynolds, Nicole.
Investigation through neutron experimentation and crystal field calculation into the connectivity of multiferroic DyMnO3 and antiferromagnetic R = [Dy, Tb, Nd, Ce].
Degree: Physics, 2013, University of New South Wales
URL: http://handle.unsw.edu.au/1959.4/53064
;
https://unsworks.unsw.edu.au/fapi/datastream/unsworks:11742/SOURCE01?view=true
► Multiferroic materials that have a unique coupling of magnetic and electronic degrees of freedom are possible candidates for the next generation of data storage and…
(more)
▼ Multiferroic materials that have a unique coupling of magnetic and electronic degrees of freedom are possible candidates for the next generation of data storage and data transfer technology. For this thesis we performed inelastic neutron scattering on an oxygen isotopically substituted sample DyMnO3. This was done in order to better understand the structural and magnetic interaction in these materials, and in an attempt to improve the magnetic signal for better performance in applications.A comparison between DyMnO3, and also multiferroic TbMnO3 to the isostructural antiferromagnetic series RVO3 R = [Tb, Ce, Dy, Nd] is carried out in order to better understand the complex correlations in the multiferroic materials. Inelastic neutron scattering experiments were performed on TbVO3, CeVO3 and DyMnO3 and results from previously performed experiments on DyVO3, NdVO3 and TbMnO3 were compared to the crystal field excitation calculations. Crystal field excitation calculations used the point charge ionic model, and were found to predict the experimental crystal field excitations, with a deviation of 0.5 meV. In TbVO3 and CeVO3 the interaction between the molecular field and the crystal field excitations is confirmed. Moreover, the point charge ionic model was found to accurately predict the properties of the crystal field excitations for the strongly correlated electron systems: RMnO3 multiferroics and the RVO3 antiferromagnetic vanadates.
Advisors/Committee Members: Ulrich, Clemens, Physics, Faculty of Science, UNSW, Mole, Richard, Australian Nuclear Science Technology Organisation (ANSTO).
Subjects/Keywords: Crystal Field Calculations; Multiferroics; Neutron Scattering
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APA (6th Edition):
Reynolds, N. (2013). Investigation through neutron experimentation and crystal field calculation into the connectivity of multiferroic DyMnO3 and antiferromagnetic R = [Dy, Tb, Nd, Ce]. (Masters Thesis). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/53064 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:11742/SOURCE01?view=true
Chicago Manual of Style (16th Edition):
Reynolds, Nicole. “Investigation through neutron experimentation and crystal field calculation into the connectivity of multiferroic DyMnO3 and antiferromagnetic R = [Dy, Tb, Nd, Ce].” 2013. Masters Thesis, University of New South Wales. Accessed January 24, 2021.
http://handle.unsw.edu.au/1959.4/53064 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:11742/SOURCE01?view=true.
MLA Handbook (7th Edition):
Reynolds, Nicole. “Investigation through neutron experimentation and crystal field calculation into the connectivity of multiferroic DyMnO3 and antiferromagnetic R = [Dy, Tb, Nd, Ce].” 2013. Web. 24 Jan 2021.
Vancouver:
Reynolds N. Investigation through neutron experimentation and crystal field calculation into the connectivity of multiferroic DyMnO3 and antiferromagnetic R = [Dy, Tb, Nd, Ce]. [Internet] [Masters thesis]. University of New South Wales; 2013. [cited 2021 Jan 24].
Available from: http://handle.unsw.edu.au/1959.4/53064 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:11742/SOURCE01?view=true.
Council of Science Editors:
Reynolds N. Investigation through neutron experimentation and crystal field calculation into the connectivity of multiferroic DyMnO3 and antiferromagnetic R = [Dy, Tb, Nd, Ce]. [Masters Thesis]. University of New South Wales; 2013. Available from: http://handle.unsw.edu.au/1959.4/53064 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:11742/SOURCE01?view=true
University of New South Wales
5.
Bertinshaw, Joel.
The role of epitaxy, chemistry and magnetic fields in multiferroic systems: Investigations with neutron scattering.
Degree: Physics, 2014, University of New South Wales
URL: http://handle.unsw.edu.au/1959.4/54167
;
https://unsworks.unsw.edu.au/fapi/datastream/unsworks:13323/SOURCE02?view=true
► The complex interplay between ferromagnetism and ferroelectricity found in multiferroic systems represents an impressive opportunity for research and technologies based upon the manipulation of both…
(more)
▼ The complex interplay between ferromagnetism and ferroelectricity found in multiferroic systems represents an impressive opportunity for research and technologies based upon the manipulation of both spin and charge degrees of freedom, but also signifies a considerable challenge to reveal the underlying mechanisms. Together, the projects presented in this thesis represent an array of innovative approaches utilising neutron scattering and complementary techniques to investigate the effect of internal and external influences upon the strong electron correlations in multiferroics with exciting potential for future spintronic applications.In thin film multilayers, where the pertinent
physics occurs within only a few unit cells from the interface, it is vital to probe the structural, magnetic and chemical properties with element and depth sensitivity. Using state-of-the-art polarised neutron reflectivity and x-ray magnetic resonant reflectivity, a clear link between modified regions of magnetism and stoichiometry is demonstrated to form at the atomically sharp interface of half metallic ferromagnet La0.67Sr0.33MnO3 / room temperature multiferroic BiFeO3.On the other side, even small influences can play a major role in exhibited ground state, enabling
new insight to be gained into intricate electron interactions. Neutron diffraction was used as a powerful tool to explore these properties. Through unique epitaxial constraints of a (110)-oriented SrTiO3 substrate and an intermediate layer of SrRuO3, thin film BiFeO3 is demonstrated to grow as a single domain system and retain the incommensurate spin cycloid found in bulk, opening an exciting
new avenue of research in thin film heterostructures. Combined neutron diffraction and theoretical modelling show that the introduction of chemical pressure through cation substitution in doped BiFeO3 significantly improves magnetic properties due to modified superexchange interactions. Finally, using in-situ applied magnetic fields with complementary neutron and bulk techniques, first evidence of potential multiferroicity is shown to arise in the spinel FeCr2S4 in the orbitally ordered state.
Advisors/Committee Members: Ulrich, Clemens, Physics, Faculty of Science, UNSW, Klose, Frank, Bragg Institute, Australian Nuclear Science and Technology Organisation.
Subjects/Keywords: Thin films; Multiferroics; Neutron scattering; Polarised neutron reflectometry; Neutron diffraction; BiFeO3; FeCr2S4; La0.67Sr0.33MnO3; Transition metal oxides; Condensed matter; X-ray magnetic reflectometry
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APA ·
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APA (6th Edition):
Bertinshaw, J. (2014). The role of epitaxy, chemistry and magnetic fields in multiferroic systems: Investigations with neutron scattering. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/54167 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:13323/SOURCE02?view=true
Chicago Manual of Style (16th Edition):
Bertinshaw, Joel. “The role of epitaxy, chemistry and magnetic fields in multiferroic systems: Investigations with neutron scattering.” 2014. Doctoral Dissertation, University of New South Wales. Accessed January 24, 2021.
http://handle.unsw.edu.au/1959.4/54167 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:13323/SOURCE02?view=true.
MLA Handbook (7th Edition):
Bertinshaw, Joel. “The role of epitaxy, chemistry and magnetic fields in multiferroic systems: Investigations with neutron scattering.” 2014. Web. 24 Jan 2021.
Vancouver:
Bertinshaw J. The role of epitaxy, chemistry and magnetic fields in multiferroic systems: Investigations with neutron scattering. [Internet] [Doctoral dissertation]. University of New South Wales; 2014. [cited 2021 Jan 24].
Available from: http://handle.unsw.edu.au/1959.4/54167 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:13323/SOURCE02?view=true.
Council of Science Editors:
Bertinshaw J. The role of epitaxy, chemistry and magnetic fields in multiferroic systems: Investigations with neutron scattering. [Doctoral Dissertation]. University of New South Wales; 2014. Available from: http://handle.unsw.edu.au/1959.4/54167 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:13323/SOURCE02?view=true
. 
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