Spin and Thermal Transport in Lateral Spin Valves

This thesis deals with three interconnected subjects all relevant to the study of spin transport in lateral spin valves (LSV): spin injection and transport; the thermal voltages that accompany spin transport; and, measurements of the spin diffusion length of a ferromagnetic nanowire. Spin injection and diffusion were examined in shadow evaporated CoFe/Cu LSVs with different CoFe electrode thicknesses, namely, 15 and 30 nm. Compared to previous studies of CoFe based LSVs, fabricated with two-step lithography, extracted spin polarisations were higher. It was concluded that this was due to the high quality transparent interfaces achieved with a shadow deposition technique and/or the slightly more Co rich composition being favourable for high spin polarisations. Thus, the potential combination of both factors is promising for achieving high spin signals. However, this work also highlighted one important caveat; a thin CoFe electrode must be used as the spin diffusion length of the Cu was strongly reduced as the amount of CoFe evaporated increased. As suggested in the literature, this was due to magnetic impurities from the electrode material being incorporated into the Cu channel during shadow deposition. Additionally, the spin injection efficiency was lower in LSVs with 30 nm thick CoFe electrodes as a consequence of the increased CoFe/Cu interface area. The thermal background voltages that arise from Peltier and Joule heating during electrical spin injection were reported and analysed as a function of temperature and electrode separation in CoFe/Cu LSVs. The contributions from the amount of heat generated, efficiency of detection, heat flow into the substrate and along the transport channel were discussed. The dramatic reduction of heat flow into the substrate was shown to dominate the device response at low temperatures. Finally, a spin absorption method was employed to determine the temperature dependence of the spin diffusion length of CoFe. Values obtained were comparable to the literature and scaled linearly with the CoFe resistivity; demonstrating that spin relaxation in CoFe occurs through the Elliott-Yafet mechanism.