2. Nanoscale magnetic semiconductor materials for spintronics.

Spintronics seeks to exploit electron spin properties instead of or in addition to the charge degrees of freedom in solid-state electronic devices. The biggest success thus far, giant magnetoresistance (GMR), has greatly increased the information storage density in magnetic hard drives and has been recently recognized by the 2007 Nobel Prize in Physics.  The full realization of spintronics with the ability to inject, manipulate and detect electron spins in semiconductor devices will revolutionize computing by offering the advantages of nonvolatility, faster data processing speed, low power consumption, and high integration densities. The realization of spintronic vision critically depends on the advances in magnetic semiconducting materials.

We have prepared previously unavailable 1-D nanomaterials and heterostructures based on concentrated magnetic semiconducting, such as europium chalcogenides (EuO and EuS) and Fe1-xCoxSi silicide alloys, and will now use this library of spin-polarized nanoscale building blocks as model systems for fundamental studies and nanodevice implementations in spintronics. We have synthesized EuO nanorods for the first time and confirmed its ferromagnetic semiconducting properties using magnetic and magneto-optical measurements. We are developing organometallic precursors and will use them to synthesize EuS and other rare earth sulfide nanowires by chemical vapor deposition through nanocluster catalyzed vapor-liquid-growth growth.

We have also synthesized NWs of magnetic semiconducting Fe1-xCoxSi alloys using the SSP approach (see above) for investigation of silicon-based spintronic nanodevices. Despite a long spin coherence lifetime and well developed materials processing, silicon-based spintronics is much less developed compared with that based on the more popular Ga1-xMnxAs dilute magnetic semiconductor (DMS). The recent discovery of magnetic semiconducting silicide alloys of Fe1-xCoxSi (0< x <1) show that silicides can be nice candidates for spin injection into silicon, not only because of their large electron spin polarization and low-to-intermediate carrier density but also because silicides are ubiquitous at interfaces between silicon and metals and widely used as contact and interconnect in the current CMOS microelectronics. We are exploiting these silicide NWs and their nanoscale heterostructures with silicon to tackle the challenges of injecting and detecting polarized electrons in silicon to realize silicon-based spintronic devices. Using nanowire nanodevices, the relationship between ferromagnetism and semiconductivity and the size evolution of their physical properties will also be investigated.

Figure 3. Characterization of Fe1-xCoxSi alloy nanowires and their magneto-transport properties.