This thesis describes the development and applications of sub-micron current-perpendicular-toplanedevices fabricated by three-dimensional etching with a focused ion beam microscope. Thistechnique was applied to a range of materials, including the study of c-axis Josephson junctionsin the high temperature superconductor Tl2Ba2CaCu2O8, the fabrication of superconductingquantum interference devices with sub-micron loop areas, and GaN light emitting diodes. Themain body of research was carried out in the study of Nb based Josephson junctions workingat a temperature of 4.2 K. Junctions with normal metal, insulating and ferromagnetic barrierswere characterised, as well as the ﬁrst metallic antiferromagnetic Josephson junctions usingγ-Fe50Mn50 as the barrier. ‘Pseudo-spin-valve’ Josephson junctions were also created using aCo/Cu/Fe20Ni80 barrier. In this case the relative orientation of the magnetic moments of theCo and Fe20Ni80 could be changed with an applied magnetic ﬁeld. The magnetoresistance andcritical current of the device showed a strong correlation, implying a direct inﬂuence of themagnetic structure of the device on the critical current.
Materials Science and Metallurgy, University of Cambridge 2003
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