Thermodynamic Behavior of Rare Earth Pyrochlores

Diplôme Thèse Thermodynamic Behavior of Rare Earth Pyrochlores eng 2020-07-20 author Turrini Alexandra 859675 director Ruegg Christian 790594 10.13097/archive-ouverte/unige:140705 urn:nbn:ch:unige-1407050 Sc. 5472 A large part of the field of highly frustrated magnetism has been devoted to studying the phases and excitations in the rare earth titanates. In this thesis, two of these materials, Ho2Ti2O7 and Tb2Ti2O7, have been investigated in terms of changes in their magnetic phase and properties of their excitations. For Ho2Ti2O7 a medium strength magnetic field directed along a <111> crystallographic direction pins spins in the triangular lattice while leaving those in the kagome lattice free to fluctuate; further strengthening the field past a critical value flips all opposing spins in the kagome plane, leaving a completely saturated 3-in/1-out magnetic monopole like quasiparticle state that terminates in a liquid-gas critical point (LGCP). To explore a supercritical crossover in magnetic monopole density extending to temperatures higher than the LGCP, we performed polarized diffuse neutron scattering measurements that separated fluctuations in the kagome plane from the perpendicular Ising-antiferromagnetic correlations in an applied field. We complemented that study with response function measurements and Monte Carlo simulations. For Tb2Ti2O7, a large thermal Hall effect signals the presence of an unusual microscopic carrier that proved difficult to pinpoint. Its energy, field, and temperature behavior pointed to a connection with the first crystal electric field excitation (CEF1) at 1.5 meV, whose zero field and low temperature behavior in an applied field have been previously investigated. We continued to investigate the behavior of this envelope at temperatures and fields relevant to the thermal Hall effect and compared it with thermal conductivity measurements to explore the relationship between its dispersion to the behavior of the thermal Hall effect. Magnetism Rare earth Frustrated magnetism Frustration Thermodynamics Supercritical Thermal Hall Dewey 500.2 Swiss National Science Foundation Frustration in Quantum and Classical Magnets 162626 CH Project funding 33 Département de physique de la matière quantique 131 false 807 Groupe Ruegg 4269be56-be3e-4ad5-b86d-1d4d5d8cdab3 Thesis Public Turrini_Manuscrit_UniGe.pdf 115611848 application/pdf Private 2022-08-26 08424fd57f49cf1bb3763c39bcac1611347647c706f21cc35f1023683c5214fb openAccess Faculté des sciences / Section de physique / Département de physique de la matière quantique

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Thermodynamic Behavior of Rare Earth Pyrochlores				2020	853	232

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Turrini, Alexandra