There are essentially two elements to this thesis, which investigates aspects of spin transport on the nanoscale. The first considers structural percolation and the ferromagnetic transition in Fe/GaAs. The second is an exploration of novel spin transport experiments. This has taken in investigations of spin-polarized scanning tunnelling microscopy, spin polarized electroluminescence and spin transport in quantum conductance in Cu nanowires. The growth of Fe on the GaAs(100)-2x6 reconstruction is studied using scanning tunnelling microscopy at room temperature. This reveals that the structural percolation occurs at a nominal thickness of 3 ML, thermal effects means that the ferromagnetic transition does not occur at room temperature until 4 ML of Fe have been deposited. This reveals that it is a combination of structural and thermal effects rather than magnetically dead layers that cause the delayed onset of ferromagnetism in Fe on GaAs. The exploration of novel spin transport effects had mixed success. Several methods of spin-polarized scanning tunnelling microscopy were tried, but no spin dependent contrast was seen. The efficiency of the spin injection process from an Fe film into GaAs was investigated, by measuring the degree of circularity polarization of electroluminescence from a buried quantum well. This method has yielded promising initial results, we have measured a net polarization from an Fe film and no polarization from a Au film. The quantum transport in Cu nanowires was investigated. The conductance of the Cu nanowires was measured by a break junction approach - tapping macroscopic wires together. This was done in the presence and absence of a magnetic field - which revealed a significant magneto-conductance effect which is totally unexpected for Cu.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599426 |
| Date | January 2004 |
| Creators | Gillingham, D. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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