Inelastic scattering and neutron polarimetry. Application to a few low-dimensioned magnetic systems

This work introduces the spherical polarization analysis used in the case of the inelastic scattering of polarized neutrons. With this kind of analysis, we are able to access some non-trivial dynamical correlation functions. Those correlation functions are related to nuclear and magnetic degrees of freedom. To study these correlations in the case of inelastic scattering, we used an optimized version of the experimental set-up called CRYOPAD (Cryogenic Polarisation Analysis Device) for which we will introduce a new calibration process. To illustrate the importance of such analysis, we will use it on two low-dimensional systems: the first one is BaCo2(AsO4)2 with a planar spin system and the second one is Sr14Cu24O41 showing both chain and ladder spin systems. The spherical polarization analysis of both elastic and inelastic signal on the compound BaCo2(AsO4)2 has allowed us to determine its low temperature magnetic structure and the nature of its magnetic excitations. With the compound Sr14Cu24O41 we demonstrated the evidence of a big anisotropy between the out-of-plane and the in-plane magnetic dynamical correlation functions for both the chain and ladder subsystems. Finally, studying the inelastic signal of the chains under a magnetic field, we tried to better understand the 'dynamical chirality' associated with clockwise and anti-clockwise precessions of a magnetic triplet. (author)