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Persistent URL http://purl.org/net/epubs/work/29682
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Record Id 29682
Title Spin-Fluctuations in Pd and Cr0.95 V0.05
Abstract Time-of-flight inelastic neutron scattering techniques have been used to measure the imaginary part of the dynamic susceptibility, Im[chi(q,q,omega)], for the incipient ferromagnet Pd, and the nearly antiferromagnetic alloy Cr0.95 V0.05. The experiments were performed on the direct geometry chopper spectrometers HET and MARI, at the ISIS spallation neutron source of the Rutherford Appleton Laboratory. Reported in this thesis are the first direct observations of so-called `paramagnons', or ferromagnetic spin fluctuations in Pd, which are seen up to ~130MeV, the highest energy measured. The strongly dispersive magnetic excitations are well described by a single-band model within the random-phase approximation. Based on our neutron scattering results and theoretical calculations we conclude that spin-fluctuation contribution to the linear term in the low temperature specific heat capacity is of the order of ~15%. For the Cr0.95 V0.05 alloy spatially coherent spin-density wave paramagnon excitations have been observed up to 400meV, the highest energy measured. Four different Lorentzian-type parametrisations of the generalised spin-susceptibility, which have featured in the literature for the cuperate superconductors,have been fitted into the data. The results of this analysis suggest that microscopic models of the spin-dynamics based on Fermi-surface nesting ideas provide an adequate characterisation of the magnetic excitations for the Cr0.95 V0.05 alloy. Also presented in this thesis is a description of the TOBYFIT program, a bespoke resolution-fitting program for analysing HET and MARI single-crystal data, and product of my CASE industrial placement at the ISIS Facility.
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Language English (EN)
Type Details URI(s) Local file(s) Year
Thesis RAL Theses RAL-TH-1998-012. 1998. 1998