Browsing by Author "Thiyagarajan, R"

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    Floating zone crystal growth and magnetic properties of bilayer manganites Pr(Sr1−xCax)(2)Mn2O7
    (Elsevier Science BV, 2012-08-15) Deng, G; Thiyagarajan, R; Radheep, DM; Pomjakushina, E; Medarde, M; Krzton-Maziopa, A; Wang, S; Arumugam, S; Conder, K
    Single crystals of a bilayer manganite series Pr(Sr1-xCax)(2)Mn2O7 (x=0, 0.4, 0.9, 1) have been grown using traveling solvent floating zone technique under various oxygen partial pressure. It was found that the crystal quality is very sensitive to oxygen partial pressure applied during growth and highly Ca doped crystals could only be obtained at elevated oxygen pressure. Whereas a secondary phase was observed for PrCa2Mn2O7 grown at oxygen partial pressure below 1 bar, a pure phase can be achieved at 8 bar of oxygen. This was evidenced studying composition mapping by X-ray fluorescence spectroscopy. X-ray Laue diffraction and X-ray powder diffraction have been carried out on the samples for the quality check of the grown crystals. Susceptibility measurements indicate that all samples are antiferromagnetic at low temperature. They also reveal the existence of two anomalies at similar to 320 K and 370 K, which coincide with the charge ordering/orbital ordering transitions described in the literature. © 2012, Elsevier Ltd.
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    High oxygen pressure single crystal growth of highly Ca-doped spin ladder compound Sr(14-x)Ca(x)Cu(24)O(41) (x > 12)
    (Elsevier, 2011-07-15) Deng, G; Radheep, DM; Thiyagarajan, R; Pomjakushina, E; Wang, S; Nikseresht, N; Arumugam, S; Conder, K
    Large size high-quality Ca-doped Sr14−xCaxCu24O41 (x=12.2, 12.6 and 13) spin ladder superconducting single crystals were grown using a modified mirror floating zone furnace with oxygen pressure up to 35 bar. The qualities of the as-grown single crystals were confirmed by polarized optical microscopy, neutron diffraction and X-ray diffraction methods. The sample compositions and homogeneity were measured using micro-X-ray fluorescence spectroscopy. The lattice parameters of each sample have been refined using the Rietveld method. The oxygen stoichiometry measurements which were performed by hydrogen reduction/thermogravimetry method show that all the three samples are slightly oxygen deficient even though high oxygen pressure was applied during growth. The high oxygen pressure is indispensible for growing highly Ca-doped Sr14−xCaxCu24O41 single crystals. The susceptibility was measured along c-axis for all three compositions, fitting well with the one dimensional dimer model, consistent with the reported values of undoped Sr14Cu24O41 parent compounds.(C) 2011 Elsevier B.V.
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    Superconductivity on a crossover phenomenon of spin–ladder system SrCa13Cu24O41 single crystals
    (Physical Society of Japan (JPS), 2014-01-01) Hisada, A; Matsubayashi, K; Uwatoko, Y; Fujiwara, N; Deng, G; Pomjakushina, E; Conder, C; Radheep, DM; Thiyagarajan, R; Esakkimuthu, S; Arumugam, S
    Electrical resistivity and alternating current susceptibility measurements were performed for the spin–ladder compound SrCa13Cu24O41 under hydrostatic pressure up to 8 GPa. The superconducting transition was observed below TC = 14.7 K at pressures above 2 GPa. By using high-quality single crystals, the bulk superconductivity with a volume fraction of 50% and temperature quadratic behavior of the normal state resistivity were observed above 3.7 GPa. They suggest that a strong interladder interaction induces the bulk superconductivity and transforms the system into a Fermi-liquid-like state. The optimal pressure was in a crossover region and the highest TC was observed without going through the bulk superconducting state. Our results suggest that the superconducting state on the crossover phenomenon presents the feature of the doped two-leg spin–ladder system because the spin gap was observed in this compound. © 2014, The Physical Society of Japan.