| Description |
This dissertation documents our experimental studies of spin-dependent electronic processes in two distinct condensed-matter systems with extremely different microscopic properties. The first of these two systems is the metallic alloy of Nickel and Iron (Ni81Fe19) known as permalloy, which is a commonly used metallic ferromagnet used routinely for spintronics applications. The field of spintronics is presently limited by the ability to generate spin currents "on demand," due to the low efficiency, high-power consumption, or difficult engineering constraints of existing techniques such as electrical spin injection, spin pumping, and optical spin alignment. One possible answer to these problems comes from the coupling between heat currents and spin currents in ferromagnets. This coupling, known as the spin Seebeck effect, might allow future spintronic devices to access a continuous supply of spin-polarized electrons simply by applying a temperature gradient to a ferromagnetic film. Analogously to the coupling between heat and charge currents (known as the Seebeck effect) that makes thermocouples and thermoelectric generators work, the spin Seebeck effect converts a heat current into a spin accumulation. We have developed and successfully applied a method for detecting this spin accumulation that is based on a highly sensitive magneto-optical Sagnac interferometer microscope, which is sensitive to spin accumulation without physical contact and without electrical artefacts. We show that this all-optical scheme can detect the elusive spin Seebeck effect in permalloy thin films, whose existence was previously debated by the field for almost a decade. Secondly, we have studied another system with rich potential applications to the fields of photovoltaics, computing, an potentially spintronics, which is amorphous hydrogenated silicon (a-Si:H). We have found several spin-dependent electronic processes that govern the time evolution of bound electron-hole pairs, and therefore affect the rates of radiative recombination or dissociation of those pairs. These mechanisms may be studied either optically or electrically, through the magnetic field effects on photoluminescence (PL) or photoconductivity (PC). By fabricating appropriate films and devices and testing their PL/PC efficiency at very large magnetic fields (up to 20T), we derive important conclusions about the role of the spin degree of freedom in the behavior of a-Si:H. |
