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Title: Crossed Andreev reflection in nanoscale ferromagnet-superconductor devices
Author: Webb, James Luke
ISNI:       0000 0004 2745 8740
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2012
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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
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available