Ferromagnetic Semiconductor Nanostructures

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This project addresses materials issues relevant to the the hybridization of conventional electronics with ferromagnetic materials, candidates for enhancing present information storage devices, as well as providing ingredients for novel electronic-like devices based on spin injection and spin manipulation (spintronics). The objective of the proposed work is to synthesize novel ferromagnetic semiconductor nanostructures in order to gain fundamental understanding of their magnetic, transport, and optical properties. Goals include: (i) comprehensive understanding of the magnetism and its relation to the semiconducting properties; (ii) higher Curie temperatures; and (iii) improved optical properties. Novel materials and structures of III-V ferromagnetic semiconductors will be synthesized in Northeastern's MBE facility. A primary focus is the exploration of transition metal ions other then Mn, beginning with Cr, but also to improve Mn containing materials. Several theoretical and experimental studies indicate that Cr in III-V materials has the potential for high Curie temperatures. The PI's group has been growing (Ga,Cr,Mn)As for about one year and has recently discovered transition temperatures as high as 700 K. Bandgap engineering will be used to facilitate the investigation of the dependence of electronic energy levels of magnetic ions. For example, Cr has an acceptor-like transition that is midgap in GaAs. By alloying antimony with arsenic, the acceptor energy can be reduced to a level comparable to Mn in GaAs. Varying the energy level of magnetic ions is important for testing and developing theoretical models of ferromagnetism in semiconductors. Magnetic and transport experiments will be used to examine the interaction between the semiconductor carriers and Cr ions. Quantifying this interaction is important for elucidating the coupling within and between magnetic polarons observed in the magnetization of (Ga,Cr)As and the carrier localization effects observed in transport measurements. %%% This project addresses basic materials research issues in a topical area of materials science with significant technological relevance, and places emphasis on the integration of research and education. The research program provides excellent opportunities for hands-on experience in the use of sophisticated scientific equipment. Graduate and undergraduate students will be involved in the design, synthesis, characterization, and science of nanostructured materials. The broad resources, and collaborative aspects, provide special opportunities for education and training of graduate and undergraduate students involved in interdisciplinary forefront research. ***