| In this thesis we exploit tunable spin energy in semiconductor structures by growing two-dimensional electron gases incorporating a small amount of magnetic ions. Such "magnetic" two-dimensional electron gases have large spin splittings between up and down electrons at low temperatures, while retaining many of the features of non-magnetic two-dimensional electron gases, such as high mobility and quantum transport. These systems are exploited to elucidate general concerns in two-dimensional physics, such as the effect of Landau level degeneracy.; Molecular beam epitaxy is used to grow magnetic two dimensional electron gases in ZnTe/Cd1-xMnxSe and ZnSe/Zn1-x-y CdxMnySe systems. Low temperature (300 mK--5K) and high magnetic field (up to 8T) magneto-resistance and Hall effect is used to characterize these systems. Further studies of photoluminescence, time-resolved Faraday rotation, and cantilever-based magnetometry are used to complement the transport measurements.; Two-dimensional electron gases in the ZnTe/Cd1-xMn xSe system exhibit a large transfer of electrons from the spatially separated electron donor regions, even for large separation between the dopants and the quantum well. Moderately high mobility (∼5000 cm2/V· s) is seen at low temperature for both magnetic and non-magnetic gases, however only non-magnetic gases exhibit any Shubnikov - de Haas oscillations.; Magnetic two-dimensional electron gases ZnSe/Zn1-x-y CdxMnySe show improved mobility over the samples used in previous studies, allowing further investigation into the nature of transport in the quantum Hall effect regime. Two regimes have been investigated: where the spin splitting is much larger than the Fermi energy, and where the two are comparable. In the first regime, the electron gas is spin polarized at low magnetic field, realizing the theorist's ideal of a spinless fermion gas. In this situation, the deepened well due to lowered Fermi level with increased magnetic field allows a field- and temperature-tunable sheet density. In the regime where spin splitting is comparable to Fermi energy, the Landau levels of spin-up and spin-down electrons can cross near the Fermi level, causing a complicated energy-level landscape. A model of non-interacting electrons strongly coupled to the manganese spins reproduces the anomalous transport and magnetization data, showing reduced conductivity by the minority spin band. |
