Engineering "Perfect" Magnets. Modern computers are based on tiny microelectronic devices such as transistors. A computer's ability to process information comes form the ability of these devices to manipulate electrons. Remarkably, this feat of engineering is achieved simply by moving electrons around using only their charge. Electrons however, in addition to having charge, also have spin. This is an abstract property of electrons but it can be visualized as the electron spinning on its own axis. Electrons can spin clockwise ("spin-up") or counter-clockwise ("spin-down"). Today we lie on the verge of a technology revolution where spin is used in addition to charge, to create spintronic devices. Some spintronic devices already exist and are used in the hard drives of computers to store and recall information. Other devices are very close to commercialization such as fast memory chips with no boot-up time. Many others are still being researched. One thing common to all of these devices is that they require a magnetic material that is used as a source of spins. Non-magnetic materials have 50% "up" and 50% "down" spins, but magnetic materials such as Fe have a spin imbalance where the number "up" is greater than the number "down". In Fe this imbalance is only 45%, a big limitation for spintronics. We would like a material with a 100% imbalance, i.e. all spin "up" electrons and no spin "down" electrons - in essence a "perfect" magnet. In a collaboration between IRG 3 researchers at the University of Minnesota, Johns Hopkins University, and Harvey Mudd College, we have deliberately "engineered" a magnet with close to perfect spin imbalance. The magnet is an alloy of CoS₂ and FeS₂ materials that have an arrangement of atoms as shown in Figure 1. The alloy composition is carefully controlled so that at a specific energy the spins are all of one orientation. This particular energy is designed to be the energy of the electrons that move when a voltage is applied to it, meaning that the electrical currents that flow through this material are perfectly polarized spin "up." Having developed this material we are now working on incorporating it into spintronic devices to capitalize on the high spin imbalance. [Wang, L.; Umemoto, K.; Wentzcovitch, R.M.; Chen, T.Y.; Chien, C.L.; Checkelsky, J.G.*; Eckert,J.*; Dahlberg, E.D.; Leighton, C. Co_1-x FexS₂: A Tunable Source of Highly Spin-Polarized Electrons. Phys. Rev. Lett. 2005, 94, 056602 (*Summer 2003 Faculty-Student Team, Harvey Mudd College)]