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Title: Magnetic characterisation of thin film NiFe/FeMn multilayers
Author: O'Reilly, S.
ISNI:       0000 0004 5372 829X
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2014
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Exchange biased thin films form the basis of many high speed electronic devices such as hard disc drives, field sensors and microwave communication devices. It is important to have a detailed understanding of the electromagnetic properties of such thin films in order to determine their suitability for specific applications. As the operating speeds of electronic devices increase the necessary characterisation range expands into' the microwave region i.e. the gigahertz frequency range. One of the most important properties in investigating thin films for potential applications is permeability. The aim of this thesis was to characterise the magnetic properties and permeabilities of exchange biased thin films. Multilayers of the structure [Ni80Fe20 (x nm)/ Fe50Mn50 (y nm)]z were deposited using a sequential sputtering system where x is the thickness of the ferromagnetic layer, y is the thickness of the antiferromagnetic layer and z is the number of times the bilayer is repeated. The hysteresis loops of the multilayers were measured using a vibrating sample magnetometer to investigate their multiple reversal stages. A two port coplanar waveguide permeameter was built to measure the permeability spectrum of the multilayers at various applied magnetic fields. The multilayer hysteresis loops exhibited a stepped structure corresponding to multiple reversals. Each reversal stage was assigned to a particular NiFe layer based on the magnetisation ratios, exchange bias and NiFe layer thickness. NiFe layers of the same thickness with the same relative position within a stack appeared to have the same value of exchange bias. The resonant permeabilities of the multilayers shifted towards higher frequencies as the applied field was increased, in agreement with ferromagnetic resonance theory. This indicated that the resonances originated from the multilayers and were not due to systematic errors or artefacts. Trends within the sample range were observed but further work is needed to confirm these observations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available