Condensed Matter Seminar

The essence of the emerging field of spin-electronics or “spintronics” is to utilize electron spin to create new microelectronic devices or increase the functionality of existing ones. One thing common to all such devices is a source of spin-polarized electrical current, most commonly a ferromagnetic material. It has therefore become a priority to develop materials that have high spin polarization at the Fermi level, P. The ideal case would be a 100 % polarized material, known as a “half-metallic ferromagnet”. Although numerous materials have been predicted to be half-metallic, an extensive experimental search has yielded few viable candidates. In this talk I will present a different approach. The idea is to “engineer” a highly polarized ferromagnet by alloy control over the electronic band structure, rather than simply searching for one based on the predictions of band structure calculations. Using a model system, Co1-xFexS2, we have demonstrated the feasibility of this concept and have achieved tunable spin polarization in the range –56 % < P < +85 %. The system has allowed us to probe the electronic, magnetic and thermodynamic properties as a controlled function of the spin polarization. I will end with a summary of our efforts to improve on this P value by increases in material quality (in stoichiometric single crystals) as well as growth of epitaxial thin films for inclusion in heterostructured devices such as GaAs-based spin injection structures.