Browsing by Author "Brown, J"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    High-resolution record of vegetation and climate through the last glacial cycle from Caledonia Fen, southeastern highlands of Australia.
    (Wiley-Blackwell, 2007-07) Kershaw, AP; McKenzie, GM; Porch, N; Roberts, RG; Brown, J; Heijnis, H; Orr, ML; Jacobsen, GE; Newallt, PR
    A blocked tributary has provided a rare site of long-term sediment accumulation in montane southeastern Australia. This site has yielded a continuous, detailed pollen record through the last ca. 140000 years and revealed marked vegetation and environmental changes at orbital to sub-millennial scales. Radiocarbon and optically stimulated luminescence (OSL, or optical) ages provide some chronological control for the last ca. 70 000 years. Most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice-covered lake conditions. The lake was surrounded by low-growing plants with an alpine character. Exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment. The two major periods of forest expansion are related to the last interglacial and the Holocene, with the third, shorter period considered to represent an interstadial in the early part of Marine Isotope Stage (MIS) 3. The latter part of the last glacial period is characterised by abrupt sub-millennial, amelioration events that may relate to documented global oscillations emanating from the North Atlantic. There are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to along-term trend towards climatic drying. © 2007, Wiley-Blackwell.
  • Thumbnail Image
    Item
    Polarized neutron reflectometry of rare-earth nitride thin films
    (Australian Institute of Physics, 2012-02-02) Brück, S; Cortie, DL; Brown, J; Saerbeck, T; Ulrich, C; Klose, F; Downes, J
    Rare-earth monopnictides like HoN, DyN, or ErN are semiconductors with typical band gaps between 0.73 and 1.3eV. The fact that they exhibit ferromagnetic ordering at low temperatures makes them possible candidates for an intrinsically ferromagnetic semiconductor [1]. Thin, polycrystalline rare-earth nitride films of 15 – 40nm thickness were grown onto c-plane sapphire substrates using low-energy ion assisted deposition. A temperature- and field-dependent polarized neutron reflectometry study in combination with SQUID magnetometry was carried out to characterize the magnetic properties of these films in a depth resolved way. The investigated samples show a homogeneous distribution of the magnetic moment throughout the film with ferromagnetic ordering temperatures comparable to the bulk materials. ErN and HoN films do not show an opening of the magnetic hysteresis loop even for the lowest measured temperature of T=2K. DyN on the other hand clearly shows a coercive field and remnant magnetization at 5K.