Quantum Transport Phenomena of Two-Dimensional Electron Sysytems in GaAs/AlGa4s heterostructures with a small Ferromagnetic Thin Film

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The purpose of the present research is to investigate the origin of the anomalous magnetoresistance observed in GaAs/A1GaAs heterostructure with a single ferromagnetic thin film in a strong magnetic field. We have investigated (1) the electron density dependence of the anomalous magnetoresistance, and (2) the effects of the local magnetic field profile produce by the ferromagnetic thin film on the anomalous magnetoresistance.In order to perform the experiment (1), we have fabricated GaAs/A1GaAs heterostructure samples with a gate electrode and varied electron density and the electron mobility simultaneously. The results analyzed on the phase diagram, electron density vs. electron mobility, show that there is no correlation between the anomalous magnetoresistance and the electron density.For the experiment (2), we have fabricated GaAs/A1GaAs heterostructure samples with different distance between a ferromagnetic thin film and the two dimensional electron systems, and with different size, thickness, and shape of a ferromagnetic thin film. The results strongly suggest that there is a correlation between the anomalous magnetoresistance and the minimum of the magnetic filed profile produce by the ferromagnetic thin film. However, we cannot explain consistently all the results of the present experiments.