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Long-range Ordering in Pr(2)NiO(4+δ) Single Crystals studied by Resonant Soft X-Ray Scattering
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Author
Francesco D'Acierno, Université de Montpellier, 2014-15
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Francesco D'Acierno
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Academic area
Mathematical and Physical Sciences
Abstract
Lanthanide oxides with the general formula of Ln2MO4+δ (where Ln = La, Pr, Nd and M = Cu, Ni, Co) are a class of perovskite oxides being part of the K2NiF4 family. As strongly correlated materials, their properties vary drastically on temperature and doping; the latter can extend over a wide range of concentration, modifying (anisotropic) oxygen mobility and valence states of the ions.
The chosen material to be investigated is Pr2NiO4+δ. Below certain critical temperatures, besides the antiferromagnetism, three- and/or two-dimensional long-range ordered superstructures can arise, creating electronically correlated states that only oxygen intercalation can induce. Those modulations are commonly referred to as static and dynamic orbital-, spin- and charge-stripe phases, i.e. wide local AFM regions divided by narrow anti-phase boundaries. They can be observed as commensurate and/or incommensurate diffrac- tion peaks by using high-brilliance X-ray sources, like synchrotron. However, their interpretation is challenging and their origin can be often confusing, due to their low intensity with respect to the structural Bragg peaks by a factor of 10−4 and the surface and bulk defects of the material, e.g. NiO segregation or Pr6O11 hydrolization. These elements provided the motivation to grow large single crystals
of Pr2NiO4+δ, in order to carry out analyses by exploiting resonant soft x-ray scattering (RSXS), a powerful technique which enhance the intensity of satellite reflections arising from competing states. By scattering with photon energies on resonance of the element’s elec- tronic transitions, RSXS is an element-specific, sensitive tool providing a combination of spectroscopic and spatial information. The thesis fo- cuses on the energy-, temperature- and polarization-dependent analysis of the ordered states measured.
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