Plastic pinning replaces collective pinning as the second magnetization peak disappears in the pnictide superconductor Ba0.75K0.25Fe2As2

Abstract

We report a detailed study of isofield magnetic relaxation and isothermal magnetization measurements with H c on an underdoped Ba0.75K0.25Fe2As2 pnictide single crystal, with superconducting transition temperature Tc = 28 K. The second magnetization peak (SMP) has been observed at temperatures below Tc/2 and vanished at higher temperatures. The observed behaviour of the SMP has been studied by measuring the magnetic field dependence of relaxation rate, R(H) and by performing the Maley's analysis. The results suggest that the crossover from collective to plastic pinning observed in the SMP disappears above 12 K with plastic pinning replacing collective pinning. An interesting H-T phase diagram is obtained. The critical current density (Jc) was estimated using Bean's model and found to be ∼ 3.4 × 10 9 A/m 2 at 10 K in the SMP region, which is comparable to an optimally doped Ba-KFe2As2 superconductor and may be exploited for potential technological applications. The pinning mechanism is found to be unconventional and does not follow the usual δl and δTc pinning models, which suggest the intrinsic nature of pinning in the compound.

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

“…4 (b) highlights the initial 15 seconds of relaxation, which corresponds to ∼ 40 % of the total magnetic relaxation in a period of 90 minutes of measurement. This feature is observed in all samples under investigation and is also found in a recent study on Ba 0.75 K 0.25 Fe 2 As 2 [30]. All magnetic relaxations follow the usual logarithmic behaviour with time, |M| ∼ log(t) and the plots of ln|M| vs lnt allowed us to obtain the relaxation rate, R = dln|M|/dlnt.…”

“…A U * vs.1/J plot has been extensively used to investigate the vortex dynamics in pnictide superconductors [30,32,33,48]. To relate the activation energy (U * ) with the critical current density (J c ), we used an expression from the theory of collective flux creep [40],…”

Strong pinning in the hole-doped pnictide superconductor La0.34Na0.66Fe2As2

“…2bshows a selected J c (H) curve at 16 K, evidencing a change in curvature as J c (H) approaches zero which was observed in all curves at higher temperatures.The same effect can be observed in the respective M(H) curves. This change in curvature (downward to upward curvature as field increases) is usually a precursor of the peak effect occurring in J c (H) curves[30], which is absent in our sample. The interesting point of this effect is that J c (H) approaches zero with a downward curvature, while usually it approaches zero exponentially (upward curvature).In order to better understand this effect we have obtained magnetic relaxation measure-ments, M(t), as a function of magnetic field and temperature.…”

“…Among the different families of pnictide superconductors, the 122class is the most relevant for high field application purposes [4]. For comparison, in the case that temperature range [30]. Therefore, it would be misleading to interpret the behaviour of R vs. T and U 0 vs. 1/J plots as a pinning crossover, because, there is no effect of such crossover in the measured isothermal M(H) curves.…”

Ginzburg–Landau Theory for Magneto‐Elastic Interaction and Magnetization in Type‐II Superconductors

“…The interaction is possibly responsible for the second magnetization peak (SMP) in the “fishtail” magnetization curve . This intriguing anomaly is also caused by plastic pinning and multigap superconductivity . It remains an open question which contribution is dominated in the SMP under certain conditions.…”