Controlled spin-polarized electron transport of oxide magnetic semiconductor films of hematite-ilumenite solid solutions by the exchange coupling

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Magnetic semiconductors are one of die promising electronics materials for the next generation, so-called spintronics materials. In this research we proposed a novel technique to control the spin-polarized transport of magnetic semiconductors and tried to realize it. The first subject was to develop thin films of new oxide magnetic semiconductors focused on a hematite-ilumenite solid solution system having a high spin polarization at room temperature. There had been many difficulties to prepare well-defined hematite ilumenite solid solution films having good magnetic semiconductive properties, because they had many controllable factors such as an order-disorder transition and Fe^<2+>/Fe^<3+> mixed valence states, etc. We found optimized preparation conditions for the solid solution films by helicon sputtering to control remanent oxygen pressure and substrate temperature precisely. The films showed magnetic semiconductive properties such as magnetoresistance at room temperature. The second subject was to control magnetic structures of ferromagnetic layers by means of a spin-flip transition of antiferromagnetic layers. Only epitaxial hematite films showed a unique spin-flip transition. We prepared hematite/spinel ferrite bilayered films by helicon sputtering and surveyed magnetic properties around the spin-flip transition. The spin-flip transition in a hematite layer disappeared because of a large in-plane magnetic anisotropy of a spinel ferrite layer. We first found the 90° exchange coupling between oxide magnetic layers. Unfortunately we could not realize the proposing spin control technique, but we could obtain huge results concerning preparation techniques for well-defined iron oxide films and their structural, magnetic and electronic properties.