ABSTRACT
Over the last two decades or more, condensed matter physics, and in particular the ¢eld of magnetism, is overwhelmingly active in the area of spintronics: the e¥ects of spin-polarized current, its generation, injection, transport, and dynamics. že amount of information generated and the discoveries that have resulted are unprecedented, reshaping not only the direction of magnetism research but also driving technological advances to dizzying heights. žousands of articles, countless reviews, and several books have been written that cover the ¢eld as it is evolving. že ¢eld is developing so rapidly and becoming so diverse that it is hard to keep up with. že driving force is the spin-polarized current generated from ferromagnetic elements, compounds, and alloys (metallic or semiconducting) due to their intrinsic exchange energy split conduction band. Generally, the degree of spin polarization (P) is limited to about 50% in conventional ferromagnetic elements and alloys materials. It can reach higher values in a special set of materials called half-metallic ferromagnets [1], which by design are quite di«cult to achieve. In this chapter, we deal with another phenomenon called spin-¢lter tunneling, currently hotly pursued for its capability to provide tunable P all the way to near 100% and can be interfaced with metals or semiconductors, giving the versatility for exploring new e¥ects.
