Doping dependence of the vortex dynamics in single-crystal superconducting NaFe${}_{1-x}$Co_xAs

Abstract

We investigate the doping dependence of flux pinning in superconducting NaFe CoxAs (x = 0.01, 0.03, 0.05 and 0.07) single crystals grown by the Bridgman method. The electronic specific heat displays a pronounced anomaly in a sample series at superconducting transition temperature, which hardly shows any residual part at low temperature. We found that Co doping plays an important role in signifying the secondary peak in the magnetic hysteresis of optimally doped (x = 0.03) and heavily doped (x = 0.05, 0.07) crystals. Furthermore, the dependence of the relaxation rate S = ∣d ln M/d ln t∣ on magnetic field and temperature exhibits a decreasing trend within a certain range corresponding to the secondary peak effect in the optimally and heavily doped samples. The magnetic relaxation rate combined with the Maley analysis of the current-dependent creep energy shows a single-vortex pinning in the lightly doped sample dominant at low applied fields, and plastic pinning at high applied fields, without showing a secondary peak. However, in the optimally and heavily doped samples, the magnetic relaxation rate and U(J) isothermal analysis show that the collective pinning that dominates below Hpeak crosses over to plastic pinning for fields above Hpeak.

Comparative study of vortex dynamics in CaKFe4As4 and Ba0.6K0.4Fe2As2 single crystals

“…The J s ðHÞ curves in Fig. 4b show the similar behavior of Na Fe 1Àx Co x ð Þ As [34] where J s ðHÞ dependence can be divided into four regimes. In the low magnetic field regime, logJ s ðHÞ reveals a small plateau.…”

Doping Dependence of the Second Magnetization Peak, Critical Current Density, and Pinning Mechanism in BaFe2–xNixAs2 Pnictide Superconductors

“…However, the mechanism responsible for SMP in Ni-doped BaFe 2 As 2 pnictide superconductors is as yet unresolved [29,36,37]. Interestingly, in iron-pnictide superconductors, it has been observed that the existence of the SMP is doping dependent [31,38].…”

“…However, the mechanism responsible for SMP in Ni-doped BaFe 2 As 2 pnictide superconductors is as yet unresolved [29,36,37]. Interestingly, in iron-pnictide superconductors, it has been observed that the existence of the SMP is doping dependent [31,38]. This motivated us to investigate the vortex-dynamics in a series of high quality BaFe 2−x Ni x As 2 (x = 0.092, 0.108, 0.12, 0.15, 0.18, 0.065) pnictide superconductors.…”

“…Contrary to the cuprates, where the SMP is mostly observed only for H || c -axis, in Fe pnictides, due to the low anisotropy, it is observed for both H || c -axis and H || ab -planes. A rich variety of mechanisms were proposed as responsible for the SMP in different iron pnictide superconductors, such as crossover from elastic to plastic, ,, order–disorder transition, , and vortex̵̵−lattice phase transitions. , However, the mechanism responsible for SMP in Ni-doped BaFe 2 As 2 pnictide superconductors is as yet unresolved. ,, Interestingly, in iron pnictide superconductors, it has been observed that the existence of the SMP is doping-dependent. , …”

Comparative study of vortex dynamics in CaKFe4As4 and Ba0.6K0.4Fe2As2 single crystals

“…show the similar behavior of Na(Fe 1−x Co x )As [34] where J s (H) dependence can be divided into four regimes. In the low magnetic field regime, logJ s (H) reveals a small plateau.…”