TY  - UNPB
A1  - Behr, Dylan
M1  - Doctoral
PB  - UCL (University College London)
UR  - https://discovery.ucl.ac.uk/id/eprint/10203584/
N2  - Strongly correlated electron systems display a complex interplay of structural, magnetic, and electronic degrees of freedom, leading to a variety of emergent phenomena. Utilising neutron and X-ray scattering techniques alongside a group-theoretical framework, I have developed and applied a unified approach to characterise this interplay in a selection of non-model 3d transition metal oxides, with a particular focus on magneto-structural coupling. I first investigate a spin reorientation transition in BiCrO?, solving its magnetic
structures and determining Dzyaloshinskii-Moriya interactions responsible for weak ferromagnetism in each phase. The interactions are demonstrated to couple spin to respective octahedral rotations and antiferroelectric distortions by a phenomenological model. I then present a study on PrMn?O??, where magneto-elastic coupling and a canted ground state are elucidated by neutron powder diffraction. A mean field model that captures the influence of competing exchange interactions on the complex ferrimagnetic ordering is developed that, together with the results, extends our understanding of magnetism in the Ał?Mn?O?? quadruple perovskite manganites. Turning to BiMn?O??, I determine a highly canted magnetic phase composed of polar E-type antiferromagnetic order superposed on a ferrimagnetic order. Modelling reveals the coupling of the polar antiferromagnetism to ferroelectric distortions, exemplifying a novel category of type I multiferroics with inverse exchange-striction. I then explore the Cu-doped BiMn?O?? systems in the half-metallic limit, employing a host of complementary experimental techniques to characterise their structural, magnetic order, disorder and transport properties. The study reveals a diverse set of behaviours across the solid solutions, marked by coexisting short and long range magnetic correlations, spin freezing transitions, near zero thermal expansion and magneto-resistance. Lastly, in a resonant X-ray study on CoTi?O?, I demonstrate near-complete antiferromagnetic domain switching under uniaxial stress, exploiting the spin Jahn-Teller to relieve its perfectly frustrated exchange topology.
ID  - discovery10203584
N1  - Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author?s request.
AV  - public
SP  - 1
Y1  - 2025/01/28/
EP  - 226
TI  - On the phenomenology of competing instabilities in selected transition metal oxides
ER  -