University of Cambridge
Magnetic and Structural Instabilities in Cerium Diantimonides under Pressure
Abstract
dc:description.abstractThe cerium diantimonides CeSb₂ and CeAgSb₂ are closely related Kondo lattice materials that are ferromagnetic at ambient pressure, unlike the majority of magnetic cerium compounds. The application of hydrostatic pressure is commonly employed to discover new phases, by continuously tuning a magnetic state, in the limit of low-temperatures, through a quantum phase transition. CeSb₂ hosts a number of distinct magnetic phases below 16 K, which initially remain relatively static under the application of pressure. However, above 17 kbar CeSb₂ enters a strongly correlated high-pressure structure, in which a new magnetic ground state can be continuously tuned to induce the onset of unconventional superconductivity and non-Fermi liquid behaviour at a quantum critical point at pc ≃ 32 kbar. A comprehensive series of high-pressure measurements have been employed to track the development of this structural transition, determine the high-pressure crystal structure and identify the magnetic ordering in CeSb₂. Structure refinements of high-pressure x-ray diffraction patterns at 300 K and ab initio numerical structure calculations point towards a pressure-induced transition from the SmSb₂ structure (Cmca) to the more compact YbSb₂ structure (Cmcm). This structure sets symmetry constraints for the possible mechanisms responsible for superconductivity in CeSb₂, and provides the foundation to perform electronic structure calculations. At 17 kbar, two magnetic transitions are detected below 3.5 K using μSR, eventually merging as they are suppressed towards absolute zero at higher pressures. These experiments indicate that the ground state in the high-pressure structure of CeSb₂ is an incommensurate antiferromagnetic ordering. This supports the interpretation that superconductivity in CeSb₂ may be stabilised by the presence of antiferromagnetic spin fluctuations at the quantum critical point. The magnetism in CeAgSb₂ can be tuned by hydrostatic pressure to a ferromagnetic quantum phase transition at pc ≃ 34 kbar. A closer study of electrical resistivity measurements around pc does resolve the onset of a suspected antiferromagnetic phase, but is unable to distinguish any characteristics of the ferromagnetic transition becoming first-order close to pc. Above pc, a downturn is observed in the resistivity at Tx ≃ 0.7 K, however, the field dependence and absence of zero-resistivity suggest that this feature is probably not consistent with superconductivity.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2024
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- de Podesta, Christian
- Advisor dc:contributor.advisor
-
- Grosche, Malte
Subjects
dc:subject × 9Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.124396
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/394380