Browsing by Author "Harker, SJ"

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    High luminosity time of flight with polarisation analysis: CeCu6
    (Elsevier, 2007-07-15) Harker, SJ; Hicks, TJ; Kennedy, SJ; Yu, DH
    The magnetic excitation spectrum of the heavy fermion system CeCu6 has been obtained by pseudo-randomly chopping the polarisation of the beam on LONGPOL and measuring the time of flight with polarisation analysis before the detectors. Separation of the magnetic part of the spectrum was made by changing the polarisation direction at the specimen. This method achieves a greater luminosity at the specimen compared with conventional methods at the expense of a background proportional to the total scattering from the specimen. The form of the spectrum is as expected with two transitions and considerable inelastic intensity centred oil zero energy transfer. The crystal field spectrum of the Ce3+ ion is considerably broadened by the Kondo nature of the system. An analysis of the experimental accuracy was made based on the statistical variation between the runs which make up the experiment. LONGPOL is a very slow instrument, based as it is on a thermal source with an incident wavelength of 3.6 A. The demonstrated possibility to obtain a spectrum incorporating polarisation analysis provides a basis to evaluate the usefulness of future implementation. © 2007, Elsevier Ltd.
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    A polarised neutron study of crystal field transitions in CeCu6
    (Australian Institute of Physics, 2004-02-04) Harker, SJ; Hicks, TJ; Goossens, DJ; Mulders, AM; Fied, Y; Yu, DH; Kennedy, SJ
    CeCu6 is a heavy Fermion compound in which the Ce magnetic moment is suppressed by the Kondo effect resulting from the admixture of the local 4f electrons with the conduction electrons. Crystal field transitions between the low-lying states of the Ce ion have been observed using inelastic neutron scattering [1–3]. The transitions were contaminated by phonon scattering which can be corrected using a complex scaling function using a complementary spectrum of LaCu6. Neutron time of flight spectroscopy with neutron polarisation analysis permits the in situ separation of magnetic and lattice vibrational energy spectra. Preliminary experiments on LONGPOL allow an indicative separation of a broadened crystal field transition and features due to lattice vibrations [4]. The preliminary analysis indicated an inelastic spin-flip feature at -12 meV which is due to the crystal field while an inelastic non-spin-flip feature at -6 meV is predominantly due to phonon scattering. A more complete polarisation analysis study has been performed using a magnetic coil to switch the polarisation at the sample position between perpendicular and parallel to the scattering vector. These results and their interpretation are reported here.