- Conference date: 19–23 December 2011
- Location: SRM University, Kattankulathur, Tamilnadu, India
I review here constant efforts of my superconducting materials group on synthesis and physical properties of title compounds from very beginning (May 2008) itself. Both direct (Fe/Co, Ni) and indirect O/F carrier doping routes are applied and superconductivity is achieved up to 14K and 50K respectively. It infers that in F doped samples the Tc is collective effect of electron doping and short range ordering of Fe spins. Whereas in Co/Ni doped samples occurrence of Tc is mainly due to electron doping. Seemingly magnetic excitations play an important role in achieving superconductivity. This along with drastic depression of Tc with Fe site Zn doping in superconducting LaFeAsO0.8 indicates towards s ± coupling. Magneto transport measurements showed that these superconductors are quite robust against magnetic field having upper critical field [Hc2(0)] of up to 400 Tesla. It is found that though FeSe/Te superconductor possesses lower Tc, the same is even more robust against magnetic field than the REFeAsO. Several future compounds with similar structure and good promises for superconductivity including BiOCuS, doped LaCo2B2, and CeNi0.8Bi2 etc. will be discussed. It is inferred from XPS (X-ray photo electron spectroscopy) that like Cu and O hybridization in HTSc, the Fe and As in REFeAsO and Fe and Se/Te in FeSe/Te play an important role. The role of Fe will be discussed by full Fe/Co substitution viz. RECoAsO and RECoPO, where interplay of RE4f and Co3d is clearly seen.
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