Spectroscopie et dynamique de spin des systèmes frustrés : des pnictides aux pyrochlores (english)

Magnetic frustration is a physical property exhibited by certain materials when the magnetic interactions are not all minimized, resulting in a degeneracy of the ground state, which can lead to exotic properties of matter, such as quantum spin liquids. In this thesis, to study these properties, we used spectroscopic methods, notably polarized and unpolarized neutron scattering. Neutron scattering is a powerful probe for observing magnetic properties. Unlike X-rays, neutrons carry a spin-1/2, making them sensitive to magnetic interactions ; it is thus possible to specifically probe magnetic structures and excitations, notably through Inelastic neutron scattering.
In the first part of this thesis, we studied the iron-based superconductor BaFe2Se3 using timeof-flight inelastic neutron scattering, as well as numerical techniques such as Monte Carlo simulations and spin wave simulations.
In the second part of this thesis, we studied the spin liquid pyrochlore compound Tb2Ti2O7 using time-of-flight and polarized triple-axis inelastic neutron scattering techniques, coupled with symmetry analysis and numerical simulations, in order to reproduce experimental data.