EuO as a perfect electron spin filter

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Vita.Includes bibliographical references (p. 93-103).Essential to the emergence of spin-based electronics is a source of highly polarized electron spins. Conventional ferromagnets have at best a spin polarization P-50%. Europium monoxide is a novel material capable of generating a highly spin-polarized current when used as a tunnel barrier. EuO is both a Heisenberg ferromagnet (Tc=69 K) and a semiconductor. Exchange splitting of the conduction band creates different tunnel barrier heights for spin-up and spin-down electrons, thus filtering the spins during tunneling. High-quality EuO films at the monolayer level is necessary for efficient spin-filtering. Because non-ferromagnetic, insulating Eu20 forms more readily, growth of an ultra-thin, high-quality film is quite challenging, which restricted previous studies of EuO to bulk form. EuO films were grown by reactive thermal evaporation, and various thin film characterization techniques were employed to determine the structural, optical, and magnetic properties, even on the thickness scale needed for tunneling (