Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals

Abstract

We report on the thermally activated flux flow dependency on the doping dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found clearly that irrespective of the doping ratio, magnetoresistivity showed a distinct tail just above the Tc, offset associated with the thermally activated flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature dependence of the activation energy follows the relation U(T, B)=U_0 (B) (1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence of the activation energy follows a power law of U_0 (B)~B^(-α) where the exponent α is changed from a low value to a high value at a crossover field of B=~2T, indicating the transition from collective to plastic pinning in the crystals. Finally, it is suggested that the 3D vortex phase is the dominant phase in the low-temperature region as compared to the TAFF region in our series samples.

References in corpus (14)

• Superconductivity in Iron Compounds
• LaFeAsO${}_{1-x}$F${}_x$: A low carrier density superconductor near itinerant magnetism
• Competing Orders and Spin-Density-Wave Instability in La(O${}_{1-x}$F${}_x$)FeAs
• Plastic vortex-creep in YBa${}_2$Cu${}_3$O${}_{7-x}$ crystals
• Iron based high transition temperature superconductors
• Very strong intrinsic supercurrent carrying ability and vortex avalanches in (Ba,K)Fe2As2 superconducting single crystals
• Control via electron count of the competition between magnetism and superconductivity in cobalt and nickel doped NaFeAs
• Critical fields, thermally-activated transport and critical current density of beta-FeSe single crystals
• Phase Diagram and Calorimetric Properties of NaFe${}_{1-x}$Co${}_x$As
• Theory of plastic vortex creep
• Thermally activated energy and flux flow Hall effect of Fe1+y(Te1-xSx)z
• Upper critical field and thermally activated flux flow in single crystalline Tl${}_{0.58}$Rb${}_{0.42}$Fe${}_{1.72}$Se${}_2$
• Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03As single crystals under hydrostatic pressure
• The upper critical field of NaFe${}_{1-x}$Co${}_x$As superconductors