Growth and characterization of Nd(Fe1-xCox)AsO single crystals

Single crystals of NdFe1-xCoxAsO with x = 0, 0.025, 0.05, 0.075, 0.10 and 0.15 were grown via high pressure synthesis. Structural and elemental analysis showed successful substitution of Co for Fe with no detectable change in the oxygen site occupation. Magnetic, electrical transport and tunnel-diode resonator measurements were used to characterize the NdFe1-xCoxAsO crystals. These measurements indicated that superconductivity was achieved with x >= 0.025 and optimal doping was established with x = 0.05 with the maximum superconducting critical temperature of 25 K. Measurement of temperature dependent resistance in applied magnetic fields as high as 14 T showed a broadening of the superconducting transition and an H-c2(T) curve that was consistent with those of other iron pnictide superconductors.