Combinatorial Investigation of Spintronic Materials
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Combinatorial
Investigation of Spintronic Materials
Y. Matsumoto, H. Koinuma, T. Hasegawa, I.Takeuchi, F.Tsui, and Young K.Yoo Abstract High-throughput synthesis and characterization techniques have been effective in discovering new materials and performing rapid mapping of phase diagrams. The application of the combinatorial strategy to explore doped transition-metal oxides has led to the discovery of a transparent room-temperature ferromagnetic oxide in Co-doped anatase TiO2. The discovery has triggered a wave of studies into other metal oxide systems in pursuit of diluted magnetic semiconductors. In this article, we describe recent combinatorial studies of magnetic transition-metal oxides, germanium-based magnetic semiconductors, and Heusler alloys. Keywords: combinatorial thin-film technology, germanium, Heusler alloys, magnetic semiconductors, oxides, spin-polarized materials, spintronics.
Introduction In the combinatorial approach to materials research, a large number of samples with different compositions are synthesized and characterized rapidly in individual experiments in order to dramatically increase the rate of materials discovery and optimization. In recent years, the combinatorial strategy has seen a growing number of applications in a variety of fields as an integral part of materials research (see the April 2002 issue of MRS Bulletin). Various thin-film techniques have been adopted for high-throughput synthesis and rapid characterization of different types of combinatorial samples. This strategy has been successfully applied in the search for advanced functional materials including superconductors1 and luminescent,2 dielectric,3 and magnetoresistance4 materials. The fabrication of thin-film combinatorial sample chips requires creating compositional variation across individual substrates. This can be achieved in a number of ways. Spatially selective shadow deposition techniques using automated shutter masks are often used, allowing fabrication of combinatorial samples with a wide variety of layout designs. In order to maximize the compositional variation that can
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be surveyed on a chip, mathematically designed mask schemes such as binary and quaternary patterns have been implemented in conjunction with precursor multilayer deposition and postannealing procedures.1–4 Alternatively, by combining shadow masking with atomic layer-bylayer deposition, in situ deposition of high-quality films can be incorporated.5 Codeposition (sputtering or evaporation) has also been used as a way of creating natural composition spreads.6–8 A critical aspect of any combinatorial investigation is the ability to rapidly characterize the properties versus composition of the combinatorial library. To date, a variety of screening techniques and instrumentation have been developed for rapid characterization of structural, compositional, optical, electrical, and magnetic properties. Magnetic materials exhibit a wide range of functionalities with immediate technological implications, and they have been the subjects of a n
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