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Title: Magnetic interactions in solid materials
Author: Vangasse, P.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1981
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This thesis is primarily concerned with the design and construction of apparatus to investigate the behaviour of non-metallic magnetic materials in their transition from a disordered to an ordered state as the temperature is reduced. The work has been directed towards making equipment - (a) to perform both Spin Echo and Fast Fourier Transform Nuclear Magnetic Resonance (FFT NMR) and (b) to establish and control the temperature of any particular sample within fine limits through the liquid helium range. The operation of the NMR spectrometer has been verified by tests using copper sulphate solution, and proton FFT NMR line-width experiments have been performed with the aim of discovering the behaviour of cobalt formate Co (H000)2.2H20, in its transition to antiferromagnetic order at 5.12 K. In fact, another material, manganese phyrophosphate, was the initial choice for investigation because of its interesting magnetic structure; however, after numerous unsuccessful attempts to grow a single crystal on the part of the author and the Radar Research Establishment, Malvern, the alternative of cobalt formate was taken up. Proton NMR line-width work on cobalt formate near its critical point is considered most useful for the purpose of classifying the material more fully and testing the predictions of recent critical phenomena theory. The results obtained in these investigations indicate a dramatic broadening of NMR lines at 5.12 K. This estimate of its Neel temperature is in agreement with the results of other researchers using non-NMR line-width methods. The theoretical background of NMR line broadening at the critical point is reviewed and the temperature dependence of NMR line-widths is derived for a model approximating the behaviour of cobalt, formate, viz, the two dimensional Ising antiferromagnet. Comparison is also made between the reported proton NMR line-width temperature variation of manganese formate and recent theory on the two dimensional Heisenberg antiferromagnet.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available