Browsing by Author "Russell, GJ"

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    Anomalous time-decay in neutron depolarization by high-Tc superconductors
    (Australian and New Zealand Institutes of Physics, 1994-11-09) Miles, PA; Kennedy, SJ; Taylor, KNR; Russell, GJ; Wang, J; Gu, GD; Takamara, K; Koshizuka, N
    In studies of the- field and time dependence of the polarisation state of a polarised neutron beam transmitted through single crystals of YBa2Cu- (YBCO) and BI2Sr2CaCu202-6 (BSCCO), we have observed some unusual behaviour for temperatures > 60*K for YBCO and 30>T>40K. The observed results suggest that at these temperatures, after removing an external magnetic field, the trapped flux density seen by the neutrons is essentially zero for all time less than = 200msecs. With increasing tune, the sampled flux density increases in magnitude, reaching the values observed in long time (20secs) measurements only after a delay of several seconds. At this time, the trapped flux density reaches a maximum and subsequently decays logarithmically at a rate determined by the effective pinning energy U(H,T). Possible mechanisms responsible for the inverse flux decay are considered. Large anisotropy in this behaviour is observed with the effect not being observed at all with Hlab for BSCCO and no marked temperature onset with YBCO with Hlab. For both YBCO and BSCCO the Hjfc observed flux decay show this behaviour. We conclude that the observed results follow, not from a change in the magnitude of the trapped flux, but rather from a change in the flux distribution within the sample. We interpret this in terms of a domain structure in the flux lattice system which is associated with the fringing closure flux which remains once the external applied field is removed.
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    An elastic recoil time of flight spectrometer for material analysis
    (Australian and New Zealand Institutes of Physics, 1994-02-10) Martin, JW; Cohen, DD; Dytlewski, N; Russell, GJ; Garton, D
    A heavy ion elastic recoil time of flight (ERTOF) spectrometer has been built on the ion beam analysis (1BA) beam line of the 8 MV tandem particle accelerator at the Australian Nuclear Science and Technology Organisation (ANSTO). The spectrometer consists of two electrostatic mirror time detectors, as described in the literature by Whitlow et. al. and Busch et al. at the forward scattering angle of 45°, and an ion-implanted surface barrier energy detector. The flight length of 750mm gives a typical timing resolution of a few hundred pico-seconds. The use of high energy heavy ions in recoil spectrometry is ideally suited to the analysis of light ions in heavy matrices, though the analysis of recoil spectra presents some ambiguity due to the overlap of individual depth profiles. An HRTOF spectrometer, with incident 77MeV 127 I 10+ as designed here, allows individual depth profiling of most elements contained within the matrix, even those in close proximity in the periodic table, therefore providing an unambiguous profile and greater certainty in sample analysis. This paper will outline the design and principles of the ERTOF spectrometer built on the IBA beam line at ANSTO. The application of this technique to materials analysis and such examples as YBCO superconductors and AlGaAs semiconductors systems will also be presented.
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    A study of transition metal implanted single crystal YBa2 Cu3 O7-δ
    (Australian and New Zealand Institutes of Physics, 1994-02-10) Martin, JW; Russell, GJ; Cohen, DD; Evans, PJ; Hartmann, A
    The modification of materials by ion-implantation is a method by which the structure and properties of a material can be altered in a controlled fashion and the study of these modified structures can lead to a better understanding of the parent material. The application to the Held of high temperature superconductors has been present ever since the discovery of the new oxides. In this study, high quality single crystal YBa2 Cu3 O7-δ was implanted separately with several different transition metal ions. The implantation was carried out using a metal vacuum vapour arc (MEVVA) ion source operated at 30kV with an approximate dose of ixlO17 ions/cm2 being applied. The resulting crystals were subsequently annealed in two separate anneal cycles in an oxygen atmosphere at 55O°C for a total of 108 hours. The sample analysis techniques involved the use of Rutherford backscattering spectroscopy (RBS), at both 2 and 3.07MeV, a.c. susceptibility measurements, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) for compositional, superconductivity, crystal structure and bonding analysis respectively. This paper will report on the results of this study which have shown that the implantation of nickel increased the rate of oxygenation in the near surface region, obtaining a transition temperature of 92°K after only 108 hours anneal time, whereas the implantation of iron was deleterious with a transition temperature of only 78°K reached after the same anneal cycles.