Superconductivity induced by Ni doping in BaFe₂As₂single crystals

Abstract

By substituting Fe with the 5d-transition metal Pt in BaFe2As2, we have successfully synthesized the superconductors BaFe2−xPtxAs2. The systematic evolution of the lattice constants indicates that the Fe ions were successfully replaced by Pt ions. By increasing the doping content of Pt, the antiferromagnetic order and structural transition of the parent phase is suppressed and superconduc-tivity emerges at a doping level of about x = 0.02. At a doping level of x = 0.1, we get a maximum transition temperature Tc of about 25 K. While even for this optimally doped sample, the residual resistivity ratio (RRR) is only about 1.35, indicating a strong impurity scattering effect. We thus argue that the doping to the Fe-sites naturally leads to a high level impurity scattering, although the superconductivity can still survive at about 25 K. The synchrotron powder x-ray diffraction shows that the resistivity anomaly is in good agreement with the structural transition. The super-conducting transitions at different magnetic fields were also measured at the doping level of about x = 0.1, yielding a slope of-dHc2/dT = 5.4 T/K near Tc. Finally a phase diagram was established for the Pt doped 122 system. Our results suggest that superconductivity can also be easily induced in the FeAs family by substituting the Fe with Pt, with almost the similar maximum transition temperatures as doping Ni, Co, Rh and Ir.

Superfluid density of Ba(Fe1-xMx)2<

“…Single crystals of Ba(Fe 0.92 Co 0.08 ) 2 As 2 and Ba(Fe 0.95 Ni 0.05 ) 2 As 2 were synthesized using selfflux method [3]. The platelets with a typical size of 2 mm × 2 mm × 0.1 mm have naturally flat and shiny surfaces.…”

“…Additional charge carriers are provided by partial replace of Ba by K [2] or substitution of Fe by Co or Ni. Concomitantly the SDW transition shifts to lower temperatures and finally superconductivity sets in [3]. Here we present a comprehensive optical study on optimal electron-doped Ba(Fe 0.92 Co 0.08 ) 2 As 2 (T c =25 K) and Ba(Fe 0.95 Ni 0.05 ) 2 As 2 (T c =20 K) single crystals.…”

“…The superconducting gap is clearly observed in reflectivity spectra for T < T c . The spectral weight analysis on optical conductivity provides information on the penetration depth and the superfluid density.Single crystals of Ba(Fe 0.92 Co 0.08 ) 2 As 2 and Ba(Fe 0.95 Ni 0.05 ) 2 As 2 were synthesized using selfflux method [3]. The platelets with a typical size of 2 mm × 2 mm × 0.1 mm have naturally flat and shiny surfaces.…”

Superconductivity by transition metal doping in Ca10(Fe1−xMxAs)10(Pt3As8) (M= Co, Ni, Cu)

“…Fig. 3 illustrates the dependency of the lattice parameters on Co-or Nisubstitution from X-ray powder data refinement, revealing similar behaviour of both Co-and Ni-1038 to the 122-type compounds Ba(Fe 1−x Co x ) 2 As 2 [26] and Ba(Fe 1−x Ni x ) 2 As 2 [11]. The in-plane axes a and b, as well as the unit cell angles (not shown) remain nearly constant within experimental accuracy, whereas c decreases by about 0.8% in the range 0 ≤ x ≤ 0.25, accompanied with shrinking of the cell volume by approximately 0.8%.…”

“…Relationships between the magneto-structural phase transition and superconductivity in iron arsenides have intensively been studied [5,[8][9][10][11][12][13][14]. In 2011 the new superconductors Ca 10 (Fe 1−x Pt x As) 10 (Pt 3 As 8 ) (1038 phase, space group P 1) and polymorphic Ca 10 (FeAs) 10 (Pt 4 As 8 ) (1048-phases, space groups P 4/n, P 2 1 /n, P 1) with critical temperatures up to 35 K were discovered [15][16][17].…”