Browsing by Author "Graham, P"

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    Inelastic neutron scattering in multiferroic materials
    (Australian Institute of Physics, 2012-02-02) Reynolds, NM; Graham, P; Mulders, AM; McIntyre, G; Danilkin, SI; Fujioka, J; Tokura, Y; Keimer, B; Reehuis, M; Ulrich, C
    Magnetism and ferroelectricity are both exciting physical properties and are used in everyday life in sensors and data storage. Multiferroic materials are materials where both properties coexist. They offer a great potential for future technological applications like the increase of data storage capacity or in novel senor applications. The coupling mechanism between both antagonistic effects, electrical polarization and magnetic polarization, is not fully understood yet. The aim of the project is the systematic study of multiferroic materials such as TbMnO3 and related materials by inelastic neutron scattering (INS) in order to obtain a deeper insight into the interplay between the two interacting effects. We have started our investigations with TbVO3, which is isostructural to TbMnO3, but has a collinear antiferromagnetic spin arrangement [1] instead of a cycloidal spin structure [2]. By using inelastic neutron scattering (INS) we have obtained the spin wave dispersion relation and the crystal field excitations of the Tb-ions in TbVO3. These data will be compared with previously obtained data of D. Senff on TbMnO3 [3]. Experiments were performed at the ILL in Grenoble, France and at the research reactor OPAL at ANSTO, Australia.
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    Understanding hydrological flow in karst to improve paleoclimate modelling of speleothems in SE Australia
    (Australian Meterological & Oceanographic Society, 2012-01-31) Markowska, M; Baker, AA; Jex, CN; Treble, PC; Anderson, MS; Graham, P
    Paleoclimate studies are an important tool to aid our current knowledge and understanding of past climatic conditions. This in turn can be used to make informed predictions about future climate change and improve natural resource management. In the last decade, paleoclimate research using speleothems has increased. Methods have been established and it has been demonstrated that they may be applied to successfully reconstruct paleoclimate records from stalagmites (Tan et. Al., 2003; Treble et. Al., 2003; Trouvet et. Al., 2009; Jex et. Al., 2011). A key parameter in the successful reconstruction of speleothem-based paleoclimate archives is the understanding of the karst hydrology influencing drip water that leads to calcite deposition (Baldini et. Al., 2006). The typically non-linear relationship between surface recharge and drip water response is highly complex and not yet fully understood (Baker and Brunson, 2003). For example McDonald et. Al. (2007) demonstrated that drips which responded simultaneously to recharge events still exhibited different delivery mechanisms and in turn exhibited discharge responses. To improve speleothems as a climate proxy, long term cave monitoring in two hydrologically different field sites in SE Australia (Wellington and Yarrangobilly caves) is being conducted. Drip water hydrology over a variety of flow regimes was characterised using over 30 drip water loggers. Distinct flow regimes and spatial variability were observed, indicating that drip waters experienced a wide variety of flow paths. It was evident that even over small spatial variations; surface to groundwater connectivity was considerably heterogeneous. To enhance the drip water study, a novel application was introduced to the cave monitoring program which used micro-temperature loggers to monitor heat signals in drip waters. This study is still in its infancy but has the potential to enhance current monitoring programs and produce greater information regarding flow regimes in speleothem formation.