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Measurements were made of the rate of magnetization, and the magnetization of the series of Dy (Co, Ni)2 compounds to investigate the intrinsic magnetic after effect. This effect is demonstrated by the existence of an intrinsic coercivity such that a critical value of applied field, Hc, must be reached before the domain walls can move freely through the material. However there is some movement of domain walls of fields below Hc, and this gives rise to time dependent magnetization. The mechanisms by which the domain walls overcome the energy barrier to their motion at fields below Hc was investigated in pulsed field, and in steady fields. After measuring the critical field and magnetic moments of each sample, the pulsed field magnetometer results were analysed to show that there is a certain temperature above which the mechanism for domain wall motion appears to be that described by Taylor???s thermal activation model. Below that particular temperature, the magnetization rate depends on the reciprocal of the applied field, and an empirical model is suggested. Estimates are made of the number of spines contained in the average wall kink; the wall jump frequency and the energy barrier. A vibrating sample magnetometer was used to study the magnetization of the specimens in steady fields. The results indicate that both the mechanisms described above are in operation, with thermal activation being a possibility at temperatures as low as 4.2K.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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Measurements were made of the rate of magnetization, and the magnetization of the series of Dy (Co, Ni)2 compounds to investigate the intrinsic magnetic after effect. This effect is demonstrated by the existence of an intrinsic coercivity such that a critical value of applied field, Hc, must be reached before the domain walls can move freely through the material. However there is some movement of domain walls of fields below Hc, and this gives rise to time dependent magnetization. The mechanisms by which the domain walls overcome the energy barrier to their motion at fields below Hc was investigated in pulsed field, and in steady fields. After measuring the critical field and magnetic moments of each sample, the pulsed field magnetometer results were analysed to show that there is a certain temperature above which the mechanism for domain wall motion appears to be that described by Taylor???s thermal activation model. Below that particular temperature, the magnetization rate depends on the reciprocal of the applied field, and an empirical model is suggested. Estimates are made of the number of spines contained in the average wall kink; the wall jump frequency and the energy barrier. A vibrating sample magnetometer was used to study the magnetization of the specimens in steady fields. The results indicate that both the mechanisms described above are in operation, with thermal activation being a possibility at temperatures as low as 4.2K.

Thesis (Ph. D.)--University of New South Wales, 1981. / Also available online.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. L.P. Gorʹkov, Florida State University, Dept. of Physics. Title and description from dissertation home page (viewed Nov. 24, 2003). Includes bibliographical references.

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No description available.