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Title: Spin transport in lateral spin valves
Author: Batley, Joseph Thomas
ISNI:       0000 0004 5917 8524
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2015
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This thesis outlines the construction of an ultra-high-vacuum angle-deposition system, developed specifically for the fabrication of lateral spin valves (LSVs). The thesis then proceeds to answer two important questions: what causes the loss of spin accumulation at low temperatures seen in LSVs? and how do spin currents interact in multi-terminal circuits? Through a double-dose electron beam lithography and angle-deposition technique, Cu/Py LSVs are fabricated and shown to have transparent contacts. By means of a DC injection method, the nonlocal voltage is measured as a function of injection current, magnetic field and temperature, enabling contributions from heat and spin currents to be isolated. The spin diffusion length is obtained from LSVs fabricated with Cu containing magnetic impurities $ < $1 ppm and $\sim$4 ppm. Temperature dependent charge and spin transport measurements provide evidence linking the presence of the Kondo effect in Cu to the suppression of the spin diffusion length below 30 K. The spin-flip probability for magnetic impurities is found to be 34\%, orders of magnitude larger than other scattering mechanisms. This is extended to explain similar observations in the spin accumulation. These measurements establish the dominant role of Kondo scattering in spin-relaxation, even in low concentrations of order 1 ppm. Finally, a new multi-terminal LSV (MTLSV) is fabricated and the interaction between two spin currents is investigated. Fan-out and fan-in measurements are performed, demonstrating that spin currents separate and combine at junctions in a circuit with magnitudes dictated by the spin resistance of the conduction channels. It is also shown that two spin currents of opposite polarity will cancel out. Whether Kirchhoff's law holds for spin currents is discussed and this chapter helps lay the ground work for spin current based circuits and computation.
Supervisor: Hickey, Bryan J. ; Burnell, Gavin Sponsor: EPSRC ; University of Leeds
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available