Browsing by Author "Kimura, H"

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    Alligator Rivers analogue project final report volume 14 radionuclide transport
    (Australian Nuclear Science and Technology Organisation, 1992) Golian, C; Lever, DA; Baker, AJ; Bennett, DG; Brandberg, F; Connell, LD; Kimura, H; Lindgren, M; Murakami, T; Ohnuki, T; Pers, K; Read, D; Skagius, K; Snelling, A
    The Koongarra orebody and its associated dispersion fan are examined as a geological analogue for the transport of radionuclides from waste repositories. The aim is to build a consistent picture of the transport that has been taking place in the orebody and the important processes controlling the retardation of uranium series isotopes and to test models of radionuclide transport. A particularly distinctive feature of the Koongarra system is the strong seasonal dependence of the groundwater flow. However, the Koongarra system is similar to a radioactive waste disposal system in that mobilization of uranium is taking place as a result of the infiltration of groundwaters that are in gross chemical disequilibrium with the mineralogy of the primary ore body. There are considerable differences between the Koongarra uranium orebody and a radioactive waste repository, particularly a deep waste repository. The Koongarra system is shallow, affected by seasonal hydrogeological changes as well as climatic variations on a longer timescale and transport is taking place in a zone of active weathering. Some of these features make the Koongarra system harder to characterise than a deep repository. However, there are nevertheless many analogies between the processes occurring at Koongarra and those occurring around a deep or shallow waste repository. The difficulties encountered because of the heterogeneity of the Koongarra weathered zone mirror those to be addressed in assessing radionuclide transport in repository systems. The 234U/238U activity ratios in rock samples from the dispersion fan decrease in the direction of groundwater transport, whereas in many other systems it has been reported that 234U is preferentially mobile relative to 238U (Osmond and Cowart, 1982; Osmond et al., 1983). As most uranium resides in the rock rather than in the groundwater, the net recoil flux of uranium daughter radionuclides is usually from the rock to the groundwater, thus leading to (234U/238U)r less than one. Other models explain the observations by invoking the presence of a phase in which 234Th is irreversibly fixed.
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    Large magnetoelectric coupling in magnetically short-range ordered Bi5Ti3FeO15 film
    (Nature Research, 2014-06-11) Zhao, HY; Kimura, H; Cheng, ZX; Osada, M; Wang, JL; Wang, XL; Dou, SX; Liu, Y; Yu, JD; Matsumoto, T; Tohei, T; Shibata, N; Ikuhara, Y
    Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi5Ti3FeO15 with high ferroelectric Curie temperature of ~1000 K. Bi5Ti3FeO15 thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi5Ti3FeO15 with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe·cm even at room temperature. © 2020 Springer Nature Limited
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    The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction
    (American Institute of Physics, 2012-10-22) Cortie, DL; Stampfl, APJ; Klose, F; Du, Y; Wang, XL; Zhao, HY; Kimura, H; Cheng, ZX
    High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120K with a (1/2 1/2 1/2) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites. © 2012, American Institute of Physics.