Appearance and disappearance of superconductivity in SmFe1−xNixAsO (x = 0.0–1.0)

Bulk polycrystalline Ni-substituted SmFe1−xNixAsO (x = 0.0–1.0) samples are synthesized by solid state reaction route in an evacuated sealed quartz tube. The cell volume decreases with increase of Ni content in SmFe1−xNixAsO, thus indicating successful substitution of smaller ion Ni at Fe site. The resistivity measurements showed that the spin density wave (SDW) transition is suppressed drastically with Ni doping and subsequently superconductivity is achieved in a narrow range of x from 0.04 to 0.10 with maximum Tc of 9 K at x = 0.06. For higher content of Ni (x ≥ 0.10), the system becomes metallic and superconductivity is not observed down to 2 K. The magneto-transport [R(T)H] measurements exhibited the upper critical field [Hc2(0)] of up to 300 kOe. The flux flow activation energy (U/kB) is estimated ∼98.37 K for 0.1 T field. Magnetic susceptibility measurements also confirm bulk superconductivity for x = 0.04, 0.06 and 0.08 samples. The lower critical field (Hc1) is around 100 Oe at 2 K for x = 0.06 sample. Heat capacity CP(T) measurements exhibited a hump like transition pertaining to SDW in Fe planes at around 150 K and an AFM ordering of Sm spins below temperature of 5.4 K for ordered Sm spins [TN(Sm)]. Though, the SDW hump for Fe spins disappears for Ni doped samples, the TN (Sm) remains unaltered but with a reduced transition height, i.e., decreased entropy. In conclusion, complete phase diagram of SmFe1−xNixAsO (x = 0.0–1.0) is studied in terms of its structural, electrical, magnetic and thermal properties.

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