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Title: Magnetic excitations in ferromagnetic nickel at low temperatures
Author: Cooper, N. S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1980
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The temperature dependence of the Fermi surface of ferromagnetic nickel has been studied by carefully measuring changes in the de Haas van Alphen (dHvA) frequencies associated with the <111> 'necks' and the <100> 'pockets' as a function of temperature between 1 and 15K. The high resolution measurement technique required the development of a broad band NMR magnetometer and an automated data collection/analysis system which are described along with the other essential features of the system. The results reveal that for both extrema, the variation of the dHvA frequency is less than 1 part in 10⁵ over the whole temperature range mentioned. It is shown that changes in the Fermi surface area are directly related to the change in magnetisation due to single particle excitations, the relationship involving quantities closely related to the electronic band structure in the neighbourhood of the Fermi level. To obtain these quantities, calculations were undertaken involving the parametrisation of a recent first principles structure and also the development of an interpolation scheme for the electron density of states in the FCC lattice. The results obtained enable us to express our experimental results as an upper limit for the single particle magnetisation at low temperatures. This limit is found to be in agreement with band theoretical arguments but at least an order of magnitude too small if the T² component of the bulk magnetisation observed in recent measurements is to be explained in terms of single particle excitations. The consequences of this discrepancy are discussed, along with other relevant experimental results, in the light of recent developments in the theory of magnetism.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available