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The recently discovered superconductor MgB2 has the highest critical-temperature (Tc) of any non-cuprate superconductor. It is also the first clear example of two gap superconductor. In this material, the presence of significant gap anisotropy, combined with Fermi surface sheets of different anisotropy leads to many unusual properties in the superconducting state. This thesis includes a study of the anisotropy in the London penetration depth, and that of Hc2 in MgB2. Unusually, these are both temperature dependent due to multi-gap effects.

Non-local effects in nanoscale devices have been of recent interest in the study of both superconducting spintronic effects and study, use and detection of pure spin currents in the normal state such as utilised in the lateral or non-local spin valve (NLSV). These devices have potential in terms of lateral integration of spintronics to electronic systems and potentially for superconducting solid state quantum entanglement, from crossed or non-local Andreev refection (CAR). Work is presented on NLSV structures fabricated by electron beam lithography and DC magnetron sputtering with in-situ Ar" ion milling of two nanoscale ferromagnetic Py nanowire electrodes in contact with a perpendicular normal/superconducting metal track, inter-electrode separation close to the spin coherence length As or the BCS coherence length ~o. Preliminary work is also presented on fabrication by resist masked shadow deposition. Local and nonlocal transport measurements have been performed to characterise both superconducting and normal state processes. The normal state NLSV effect for a Cu/Py device has been measured and values are presented for As and spin polarisation P for tunnelling and Ohmic junctions. Measurements of electrode anisotropic magnetoresis- tance (AMR) are shown, aiming to create an ideal electrode anti parallel magnetisation to separate CAR from competing elastic cotunnelling (EC). Poor magnetic switching be- haviour was observed; the results of investigations performed to determine the cause for Py nanowire structures is presented in conjunction with micromagnetic simulation. Measurements taken at sub-lK are shown, with good evidence of CAR for PylAI devices. Distinction between CAR, EC and charge imbalance (Cl) is detailed through measurements as a function of injected current, temperature and magnetic field compar- ing to literature experiments and theoretical models. Evidence is presented of CAR in Ta, not previously observed. A proposal is made for a potential new geometry for realising non local effects for shorter coherence length superconductors. 3

This thesis presents work carried out to design, build and test a superconducting fault current limiter (SFCL) of the resistive type utilising magnesium diboride (MgB2) in round wire form. It is believed to be the first time such a device has been manufactured. Electromagnetic design of the superconducting coil of the SFCL was carried out to minimise inductance and to evaluate the forces on, and magnetic flux density within, the conductors. A former was designed on which to wind the coil, taking into account the thermal performance, coil winding and manufacturing processes of the SFCL. Thermal performance of the SFCL during current limiting action was modelled using finite element (FE) software. A comprehensive test programme was carried out on the manufactured SFCL prototype. Separate constant voltage and constant current test circuits were built for this purpose. Data acquisition and control was provided by a PC based LABVIEW system. Tests showed that the MgB2 wire transitioned from a normal state resistance of O.31Wm to superconducting at a temperature of 37.SK. Good fault current limiting characteristics were displayed; currents above 180Apeak being limited when operating at a temperature of 30K. The current limiting process was seen to be consistent and repeatable, with the SFCL thermally recovering superconductivity between tests. The current level at which limiting was initiated could be controlled by the operational temperature, with lower temperatures giving a higher current level at which limiting begins. High voltage tests demonstrated that the prototype design was capable of withstanding approximately 15kV in air and in excess of 30kV in liquid nitrogen. Good thermal stability to long-cycle quench tests was also demonstrated; current was limited for up to 1.6 seconds without any degradation to the superconducting wire. Negligible temperature rise was measured in the SFCL during rated operation. When power dissipation calculated from experimental results was used in the thermal FE model, an average temperature rise in the region of from 30K to 65-8SK in the MgB2 wire was predicted during the first cycle of current limitation. A software model of the SFCL was made which accurately predicts the response of the SFCL to a fault current. This model has been optimised for inclusion in power network analysis models. Alternative MgB2 wire samples were tested for suitability in SFCL applications. These samples all showed good current limiting characteristics. Wire sheath material was seen to have an important impact on quench homogeneity and the developed current limiting resistance.