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Title: Grain boundary perovskite devices
Author: Isaac, Stephen Paul
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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The perovskite family has many novel features including, in certain compounds, either high temperature superconductivity or colossal magnetoresistance (CMR). The electrical and magnetic properties of grain boundaries in these materials also have their own unique properties. These distinct characteristics can be exploited to make devices with a range of potential applications. In this thesis, two types of devices are presented. Superconducting grain boundaries have been studied extensively and can form Jospehson junctions. The grain boundaries have a reduced supercurrent but a substantially enhanced sensitivity to magnetic fields relative to the bulk material. As current in nearby control loops can generate magnetic flux in the grain boundary, Josephson vortex flow transistors can be made. The properties of one type of this device are presented as a function its shape and relative dimensions. Tapering the junction width is shown to produce a substantial current gain over a significant field range. These devices can be used as current based logic gates. In 1995, reports of the low magnetic field response in polycrystalline films of the CMR manganites were published. These low-field effects were attributed to the grain boundaries present in the granular materials. To isolate and maximise this response, a Wheatstone bridge structure has been patterned into various bicrystal CMR films. The properties of the grain boundaries are reported as a function of temperature, the magnitude and orientation of the magnetic field, and also as a function of the grain boundary angle. CMR grain boundaries may replace the giant magnetoresistive read heads which are the current state of the art in magnetic read head technology. The possibility of a common transport mechanism in these two types of materials has been explored and several similarities have been found to exist.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available