Role of orbital hybridization in the magnetism of nanoscale oxides
| dc.contributor.author | Vinod Kumar, Paidi | |
| dc.contributor.examiningcommittee | Southern, Byron (Physics and Astronomy) Burgess, Jacob (Physics and Astronomy) Nemykin, Viktor (Chemistry) Sham, Tsun-Kong (University of Western Ontario) | en_US |
| dc.contributor.supervisor | van Lierop, Johan (Physics and Astronomy) | en_US |
| dc.date.accessioned | 2019-10-03T19:46:29Z | |
| dc.date.available | 2019-10-03T19:46:29Z | |
| dc.date.issued | 2019-10-03 | en_US |
| dc.date.submitted | 2019-09-14T22:00:28Z | en |
| dc.date.submitted | 2019-10-02T20:04:20Z | en |
| dc.degree.discipline | Physics and Astronomy | en_US |
| dc.degree.level | Doctor of Philosophy (Ph.D.) | en_US |
| dc.description.abstract | Orbital degrees of freedom, coupled with the spin of an electron, play a fundamental role in magnetism. In this dissertation, I present an answer to an open question in the magnetism of nanoscale oxide systems: When oxygen ions surround a metal ion, what is the role of metal ions hybridized with oxygen in the magnetism? To begin with, two different classes of materials that are mixed valent in nature were chosen (d electron rich and d0 systems) for this study, and their electronic structure and magnetism probed using atomic, elemental, and bulk sensitive techniques. Using x-ray absorption spectroscopy and x-ray magnetic circular dichroism of Fe3O4 and CoFe2O4 (d electron rich) the origin of magnetic moment is associated to the spin of the electrons. The orbital angular momentum was mostly quenched due to the crystal field splitting of the d orbitals. In-situ magnetic susceptibility measurements performed under oxygen rich and oxygen deficient environments showed that partial pressure of oxygen disrupts the exchange pathway of Fe/Co – O2- – Fe/Co, leading to an enhancement of magnetization in CoFe2O4 compared to Fe3O4. In d0 systems (CeO2 shapes) the in-situ magnetic susceptibility measurements showed that depending on the amount of oxygen present in the lattice and surface of the nanoceria a redox transformation (Ce4+ ↔ Ce3+) occurred via oxygen vacancy formation and provided a window to quantify the defects. Electronic structure and element specific magnetism studies showed that in nanoscale CeO2 the Ce 4f – O 2p states are hybridized. A comparison between the element sensitive and overall magnetism shined light on the origin of magnetism in these nanoscale systems evidencing that hybridized states captured in the vacancy orbitals play a critical role in mediating the long-range magnetism. This work demonstrates that this hybridization concept may be a solid foundation for understanding the weak ferromagnetic-like response that is observed in several non-magnetic oxides (where O 2p hole states are key players, and their hybridization with host or guest metal ions changes the density of states) that present similar magnetism. | en_US |
| dc.description.note | February 2020 | en_US |
| dc.identifier.uri | http://hdl.handle.net/1993/34321 | |
| dc.language.iso | eng | en_US |
| dc.rights | open access | en_US |
| dc.subject | Physics | en_US |
| dc.title | Role of orbital hybridization in the magnetism of nanoscale oxides | en_US |
| dc.type | doctoral thesis | en_US |