The fluctuation effect of BaFe_1.8Co_0.2As₂single crystals from reversible magnetization

Abstract

We present reversible magnetization measurements for applied fields in the range from 0.5 to 7 T made while varying the temperature for optimally doped BaFe1.8Co0.2As2 single crystals with Tc = 23.6 K. The rounding fluctuating magnetization was observed in the reversible range of magnetization for temperatures above 18 K. This fluctuation effect is quite small compared with that in high temperature cuprate superconductors, but is still large enough for obtaining the essence of the physical properties in this iron pnictide superconductor. This reversible magnetic fluctuation follows a three-dimensional scaling form in the critical fluctuation region for fields above 0.5 T, which indicates that this iron pnictide superconductor belongs to the class of three-dimensional superconductors.

Anisotropy dependence of the fluctuation spectroscopy in the critical and gaussian regimes in superconducting NaFe1−xCo x As single crystals

“…In the case of the x  = 0.03 crystal, the region where the 3D scaling is applicable is in excellent agreement with the prediction. The 3D scaling was also previously observed under similar field amplitudes in the fluctuation-induced magnetic susceptibility of a crystal of the same composition 16 , in single crystals of other iron-pnictide families 6,8,12,14,19,20 , and also in high- T c superconductors like optimally-doped YBa 2 Cu 3 O x 5,36 . In the case of the x  = 0.07 and 0.073 crystals the 3D-LLL scaling fails before reaching the Ginzburg criterion.…”

Paraconductivity of the K-doped SrFe2As2superconductor

“…We note that these results have been obtained for two K contents: x = 0.28 and x = 0.25. A similar trend has been observed in optimally doped BaFe 1.8 Co 0.2 As 2 single crystals: the scaling form of the fluctuation magnetization observed for this sample indicates that the fluctuation magnetization follows a 3D scaling form in the critical fluctuation region for a suitable applied magnetic field, suggesting that this iron pnictide material belongs to the class of 3D superconductors [24].…”

Evidence of 3D fluctuations in magnetization of BaFe1.25Ru0.75As2 single crystal

“…From figure it is clear that ZFC and FC magnetization bifurcate over a large temperature range and that they have a small region of reversible magnetization. Based on LLL approximation, the thermodynamic quantities can be described by scaling law with a variable A(T-T C (H))/(TH) n , where A is a temperature and field independent coefficient, T C (H) is the mean field temperature and exponent n=1/2 for 2D (high field) or 2/3 for 3D (low field) regime [3,5]. To perform the scaling analysis of each curve, the temperature and magnetization were replaced by their scaling forms (T-T C (H))/(TH) n and M/(TH) n respectively.…”

“…The temperature range in which fluctuations are important depends upon the dimensionality of the system and the Ginzburg parameter. Superconducting fluctuations occur near T C and manifest as a rounding of magnetization and electrical conductivity near the superconducting transition [1,3]. These fluctuations are seen to exist in both electron doped Ba(Fe,Co) 2 As 2 [3] and hole doped (Ba,K)Fe 2 As 2 [4] systems, with a 3D scaling behavior for reversible magnetization near T C .…”