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On the hierarchy of electronic and magnetic energy scales in novel 3d, 4d and 5d transition metal oxides probed by X-ray techniques

Pincini, Davide; (2019) On the hierarchy of electronic and magnetic energy scales in novel 3d, 4d and 5d transition metal oxides probed by X-ray techniques. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Transition metal oxides (TMOs) represent the natural playground for the investigation of the exotic phases produced by electronic correlations, which include high-temperature superconductivity, giant magnetoresistance and topological insulators. The peculiar electronic and magnetic properties of TMOs stem from the interplay between the electron-electron correlations, the crystal field and the spin-orbit coupling (SOC) of the transition metal (TM) d valence electrons. The balance of these energy scales significantly depends on the TM element considered: moving from the 3d to the 5d row of the periodic table, the electronic correlations decrease due to the larger size of the atomic orbitals, while SOC increases as a result of the increased atomic charge. In this work, I present three separate case studies of 3d, 4d and 5d TMOs which highlight the impact of the competing interactions just mentioned on the electronic and magnetic properties of the system. Concerning 3d TMOs, I investigate the magnetic ground state of a family of weak ferromagnets, where the weak SOC is responsible for the appearance of a net magnetisation in the main antiferromagnetic order. I then examine the intermediate case of the 4d oxide Ca2RuO4. Here, electronic correlations, SOC and octahedral distortions act on an equal footing to determine the TM ground state. In particular, I show how the crystal field tuning achieved by La substitution affects the electronic and magnetic properties. Finally, I address the spin-wave spectrum of the electron-doped perovskite iridate (Sr 1-x La x)2IrO4, where the strong SOC of 5d electrons gives rise to a spin-orbit entangled Mott state with peculiar exchange interactions. Most of the experimental findings are the results of measurements performed by means of several synchrotron radiation scattering and absorption techniques: the latter proved to be extremely powerful and versatile in the investigation of many aspects of the physics of the systems discussed.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: On the hierarchy of electronic and magnetic energy scales in novel 3d, 4d and 5d transition metal oxides probed by X-ray techniques
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms.
Keywords: Synchrotron, X-ray scattering, X-ray absorption, Transition metal oxides, Spin-orbit coupling, Magnetism, Carbonates, Ruthenates, Iridates
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10063729
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