KSEF RDE: Investigation of a new Class of High-Temperature Ferromagnetic Semiconductors

Novel materials are necessary to underpin cutting-edge technologies with commercial value. There is now considerable effort to develop "spintronics", in which the spin of charge carriers is exploited to provide enhanced functionality for microelectronic devices. A key goal is the discovery of room-temperature, ferromagnetic semiconductors to fabricate spin- based field effect transistors, spin-based light emitting diodes, and magnetic random access memory. If suitable materials can be found to implement these new devices, they would ensure a revolution in electronics and information technologies. "Dilute magnetic semiconductors", such as GaAs and ZnO doped with 3d-elements, are under intense study as prospective materials for spintronic devices. Although their Curie temperatures now approach room temperature, the weak solubility and segregation of magnetic ions in the host semiconductors makes them impractical. Therefore, it is crucial to discover novel room-temperature ferromagnetic semiconductors having a dense, periodic array of magnetic ions. We have discovered that ruthenium ferrites (Ba,Sr)Fe2+~Ru4±~Oi1 simultaneously exhibit narrow-gap semiconductivity and ferromagnetic order well above room temperature. Tailoring of physical properties can be achieved by chemical substitution of Fe by Co. These materials provide an excellent opportunity to conduct thndamental theoretical and experimental studies of the mechanism of high-temperature ferromagnetism in semiconductors; and they present an entirely new paradigm to generate an ensemble of isostructural materials having varied properties of commercial interest. Our initial data support high anomalous Hall conductance and carrier concentration, low resistivity, and compatibility with Si, and clearly suggest that these materials are a potential alternative to dilute magnetic semiconductors. We will undertake the following investigations to veri1E~t the commercial promise of(Ba,Sr)Fe2±~Ru4±~Oii: 1) Optimize magnetic and semiconducting properties by chemical substitutions of Fe by Co 2) Investigate the magnetic homogeneity and microstructure 3) Investigate the compatibility of thin films with commercial substrate materials