Thesis presented January 06, 2017
Abstract: In this thesis, we have studied the evolution of the Fermi surface under the influence of a magnetic field in bulk materials that can be easily polarized at low temperature. The first part was devoted to the cases of the ferromagnetic superconductor UCoGe with a magnetic field applied along the easy magnetization
c-axis and the paramagnetic superconductor CeIrIn
5 with the field along the c-axis. In UCoGe, several successive anomalies were detected in resistivity, Hall effect and thermoelectric power, without any thermodynamic transition being detected in magnetization. The direct observation of quantum oscillations showed that these anomalies are related to topological changes of the Fermi surface, also known as Lifshitz transitions. In CeIrIn
5, the thermoelectric power detected an anomaly at
HM = 28 T and the quantum oscillations observed in torque magnetometry showed that a Lifshitz transition occurs at this field. In the second part of this thesis, we studied the evolution of the Fermi surface through first order magnetic transitions induced by magnetic field. In the ferromagnetic superconductor URhGe with the field applied along the hard magnetization b-axis and the antiferromagnetic superconductor UPd
2Al
3 with the field in the basal plane. In URhGe, the thermoelectric power allowed to observe a change in the Fermi surface at the spin reorientation transition at
HR = 11.75 T defining the ferromagnetic state and along with resistivity confirmed the first order character of the transition as well as give a location of the tricritical point. In UPd
2Al
3, a new branch was observed in de Haas-van Alphen experiment in the antiferromagnetic phase and the thermoelectric power showed that the Fermi surface is reconstructed at the metamagnetic transition at
HM = 18 T where the antiferromagnetic state is suppressed and could suggest that the Fermi surface changes before this transition. Additionally, four new branches were observed in the polarized paramagnetic phase, above HM, that cannot be associated with calculated branches in the paramagnetic of antiferromagnetic states.
Keywords: Magnetism, Electronic Correlations, Nernst Effect, Superconductivity, Heavy Fermions, Thermoelectricity
On-line thesis.