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Cyrille Boullier

Inelastic scattering and neutron polarimetry

Published on 21 October 2005
Thesis presented October 21, 2005

This PhD report introduce 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'll introduce a new calibration process.
To illustrate the importance of such analysis, we'll 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 sybsystems. 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.

Polarimetry, Inelastic Diffusion, CRYOPAD, Spin Scales, Low-dimensional Magnetism, Nuclear-Magnetic Interference, Hybrid Correlation Functions, Chirality

On-line thesis.