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Modélisation expériementale des matériaux magnétiques moléculaires : études combinées par diffraction X, neutrons et neutrons polarisés

Abstract : We developed a model and a refinement program for charge and spin densities. During the first tests several difficulties have arisen and have been investigated and solved by implementation of constraints. After the establishment of stable joint refinement program, we tested it on the MnCu(pba)...(H2O)3...2H2O, with pba = 1,3-propylenbis(oxamato) complex reusing data from an experiment of polarized neutron diffraction and making a new experience of X-ray diffraction at 10K. This study tested three weighting schemes and constraints. These tests showed that the joint refinement give access to the same results as the separated refinements but also allow us to go further by refining the spin density with more pertinent parameters. Following these initial tests, we were interested in a copper azido complex (Cu2L2(N3)2 with L=1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2-onato). The joint refinement give us access for the first time to the experimental spin-resolved valence density and also to refine the parameters of contraction / expansion for spin up or spin down separately. In the last chapter we studied a cobalt complex which shows interesting magnetic properties. However, the magnetic properties of the compound come from a high magnetic anisotropy which complicates a study by joint refinement. That is why we studied only the charge density of this compound. This study still allowed to show experimentally a torsion angle of 39° between the principal axes of the cobalt atoms, which was predicted by a previous theoretical study
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https://hal.univ-lorraine.fr/tel-01749346
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Maxime Deutsch. Modélisation expériementale des matériaux magnétiques moléculaires : études combinées par diffraction X, neutrons et neutrons polarisés. Autre [cond-mat.other]. Université de Lorraine, 2012. Français. ⟨NNT : 2012LORR0150⟩. ⟨tel-01749346⟩

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