Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis presents an attempt at creating a fully functional SQUID for the purposes of a predefined application. The goal of the work is to provide a method of development, primarily utilising the facilities of the Engineering Faculty of the University of Stellenbosch, with minimal assistance from other departments. This method is then analysed and the successes and failures discussed in order to provide guidelines and recommendations for future research. The device consists of a gradiometric SQUID, as well as electronics which provide the SQUID bias current, output linearisation and output signal filtering. YBCO is used for the superconducting material, allowing the use of liquid nitrogen as coolant which eases the operation and portability of the device. Various methods of creating Josephson junctions are tested, such as constriction bridges using AFM lithography and step-edge junctions, with and without different buffer layers. Proof of concept simulations demonstrate the viability of the device. Unfortunately, a functional device could not be constructed, mostly due to the design requiring higher levels of resolution and process control than some of the available facilities can provide. Recommendations are provided for future researchers. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf ’n poging om ’n volledige funksionele SQUID te vervaardig vir die doeleindes van ’n vasgestelde toepassing. Die doel van die werk is om ’n metode te voorsien wat hoofsaaklik gebruik maak van die fasiliteite van die Ingenieurswese Fakulteit van die Universiteit van Stellenbosch, met minimale hulp van ander departemente. Hierdie metode word dan ondersoek en die suksesse en mislukkings bespreek om riglyne en voorstellings te voorsien vir toekomstige navorsing. Die toestel bestaan uit ’n gradiometriese SQUID, sowel as elektronika wat voorsiening maak vir voorspanning, uittree-linearisering en ’n uittree-filter. YBCO is as supergeleidende materiaal gebruik, wat die gebruik van vloeibare stikstof as verkoeler moontlik maak en dus die hantering en draagbaarheid van die toestel vergemaklik. Verskillende metodes om Josephson-vlakke te vervaardig is getoets, onder andere vernouingsbrugvlakke deur middel van AFM litografie en stapvlakke met en sonder bufferlae. Bewys van konsep simulasies demonstreer die lewensvatbaarheid van die toestel. Ongelukkig kon ’n funksionele weergawe van die toestel nie vervaardig word nie, hoofsaaklik as gevolg van die ontwerp wat hoër resolusievlakke en beter prosesbeheer benodig as wat sekere van die beskikbare fasiliteite kan voorsien. Aanbevelings word voorsien vir toekomstige navorsers.

Magnetic properties of Nb/Ni superconducting (SC) / ferromagnetic (FM) multilayers exhibit interesting properties near and below SC transition. A complex Field (H) – Temperature (T) phase boundary is observed in perpendicular and parallel orientation of ML with respect to DC field. We address the critical need to develop methods to make reliable magnetic measurements on SC thin films and ML, in spite of their extreme shape anisotropy and the strong diamagnetic response of the SC state. Abrupt, highly reproducible “switching” of the SC state magnetization near the normal-state FM coercive fields has been observed in Nb/Ni ML. The SC penetration depth l(Nb) > the SC coherence length xo(Nb) » 40 nm >> the FM layer thickness y(Ni) = 5 nm, abrupt magnetic reversals might be driven by strong supercurrent densities (J x M torques) that have the potential to flow into the Ni layers. Alternatively, sharp magnetization anomalies also can result from strong flux pinning by the periodic layered structure of ML, including “lock-in” of quantized flux lines (FL) parallel to the ML plane. Strong confinement of the supercurrents within ML planes might also lead to various phase transitions of the FL lattice (FLL) composed of one-dimensional chains and other unusual structures. Possible mechanisms for the switching anomalies must be evaluated while considering other experimental properties of Nb(x)/Ni(y) ML: 1) The upper critical magnetic field Hc2(T) exhibits a highly unusual anisotropy where the SC transition temperature Tc (H®0) for DC field H ^ ML plane exceeds the value for H || ML by ~ 0.5 K. 2) Nb/Ni ML samples do not consistently exhibit magnetic signatures for the onset of superconductivity, depending on the details of the sample mounting procedure and the AC or DC method used in SQUID magnetometry experiments. 3) Unusual “wiggles” or oscillations of order 10-30 mK were observed in Hc2(T) in AC SQUID experiments with H || ML and can be even larger (~0.16 K), depending upon the AC drive amplitude ho and frequency f .

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Two sites around the Maricopa and Sierrita Mountains respectively were investigated to provide supporting data for the State of Arizona proposal to the Department of Energy to construct a Superconducting Super Collider (SSC) facility. The main feature of the facility is a 53 mile racetrack shaped tunnel. The proposed Maricopa SSC tunnel passes through three main types of rock--approximately 35 miles of indurated fanglomerates, 10 miles of granodiorites and 8 miles of volcanic and sedimentary rocks. The proposed Sierrita SSC tunnel also passes through three main rock types--approximately 19 miles of indurated fanglomerates, 18 miles of granodiorites and granites and 16 miles of volcanic and associated rocks. Data were obtained from three sources--existing data; field investigations including drill logs and geophysics and laboratory testing. Empirical design approaches were compared with rock classifications (RQD, RMR, Q) at the tunnel horizon. Results indicate mostly routine tunneling at both sites. Recommendations are made for: further logging and testing of existing core; further field mapping; additional boreholes in rock and alluvium; and in situ testing of alluvium.

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