Abstract
A comprehensive study of magnetisation reversal mechanisms in thin films suitable for magneto-optic recording has been completed. Novel Tb/Fe multilayer and DyFeCo alloy thin films suitable for use in current systems along with Co/Pt multilayer films regarded as being appropriate for the next generation of magneto-optic media have been studied. A furnace has been built for a commercial alternating gradient force magnetometer and measurements performed at high temperatures to study reversal during the thermomagnetic writing process. A magnetic force microscope has been used to obtain images of domains and a correlation found between their structure and the magnetic characteristics displayed by samples.Irreversible susceptibility curves have been calculated from remanence data obtained at room and elevated temperatures. These have been applied extensively to describe reversal mechanisms in terms of the energy barriers to reverse domain nucleation and domain wall motion used with the two coercivity model. The effect of the demagnetising field on magnetisation reversal due to applied fields and with time has been discussed in depth and found to influence reversal strongly. Domain wall pinning has been related to the microstructure of films and found to influence reversal strongly along with the demagnetising field on both macro and microscopic scales. Additionally demagnetisation by the DC cyclic erasure process has been demonstrated to be as effective as AC demagnetisation therefore al1owing the study of domain wall processes at high temperatures. The use of ΔM curves to investigate interaction mechanisms has been shown to be restricted to applied fields where reversal mechanisms can be clearly identified. Where applicable these interaction mechanisms have been discussed. Strong dipolar coupling between domains has been shown to overcome domain wall pinning to reduce internal flux resulting in a reduction in domain size when the applied field cancels the overa11 demagnetising field of a sample. A preliminary comparison of activation and Barkhausen volumes has revealed these quantities to be of the same order of magnitude although further investigation is required.
| Date of Award | 7 Sept 1998 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Engineering and Physical Sciences Research Council (EPSRC) |
| Supervisor | Kevin O´Grady (Supervisor) |