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Title: A Mossbauer study of the spin-flop phase transition in some antiferromagnetic materials
Author: Pankhurst, Q. A.
ISNI:       0000 0001 3466 6212
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 1986
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The spin-flop phase transition has long been of interest to both theoretical and experimental physicists, ever since it was first predicted by Louis Neel in 1936. In this work spin-flop transitions in the antiferromagnetic materials K 2 FeF 5 , Rb 2 FeF 5 and a-Fe 2 0 3 have been 57 studied by means of Fe MBssbauer spectroscopy. Spectra of K2FeF5 and Rb2FeF5 single crystals were recorded at 4.2K with external magnetic fields of up to 14T applied in different modes, providing information on the effect of misalignment on the sharpness or 'order' of the observed transition. Directing the applied field parallel to the easy anisotropy axis resulted in a sharp 'first-order' transition, while misaligning the field by ~30o produced a broadened 'second-order' transition. Field-induced spin-flop transitions in a-Fe203 single crystal samples were studied at low temperatures by applying fields of up to lOT either parallel to or perpendicular to the easy anisotropy axis. The observed transitions were found to be of first-order in the 'parallel' case, and second-order in the 'perpendicular' case. The Morin transition, a temperature driven spin-flop which occurs naturally in a-Fe 2 0 3 at ~260K, was also studied and was found to be of first-order. Comparison of the character of the observed transitions with the predictions of several theoretical models of the spin-flop led to the conclusion that the conventional mean-field theory of the transition provides a good qualitative description of the phenomenon.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Solid-state physics