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Title: The effects of anisotropy on the long-wavelength excitations of itinerant ferromagnets
Author: Godfree, John A.
ISNI:       0000 0001 3501 3344
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1993
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In this thesis I present a formalism for calculating the effects of magnetic anisotropy on the long wavelength excitations of a magnetically ordered itinerant electron system. It is derived from a relativistic multiple scattering theory treatment of the density functional formalism single electron equations. Multiple scattering theory is shown to be capable of describing the small anisotropy energies involved via work on the effects of anisotropy on magnetic interactions between magnetic impurities embedded in a non-magnetic metallic host. The addition of a third, heavy non-magnetic impurity is found to enhance the magnetic anisotropy energy of a magnetic pair in the system such that in some cases it becomes comparable in magnitude to the effective exchange energy. The resulting anisotropic magnetic interaction is found to be more complex than that shown by other model calculations. In attempting an investigation of the magnetic excitations by constructing a relativistic dynamic susceptibility-from a two electron Green’s function, it is found that solving the Kohn-Sham-Dirac single particle equations together with the Local Density Approximation in this situation leads to an inconsistency. As a result of this, the starting point for the subsequent analysis is the phenomenological equation of motion for a magnetic moment. It is known that one of the effects of magnetic anisotropy on the excitations is the existence of a gap in the spin-wave dispersion spectrum. The formalism gives the correct result in the non-relativistic limit, an absence of a gap, and is evaluated numerically for bcc iron, fee nickel and fee cobalt when relativistic effects are included. The results compare favourably against previous magnetic anisotropy calculations and experimental work.
Supervisor: Not available Sponsor: Science and Engineering Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QA Mathematics ; QC Physics ; QD Chemistry ; TK Electrical engineering. Electronics Nuclear engineering ; TN Mining engineering. Metallurgy