On the nature of the second magnetization peak in FeSe_1−xTe_xsingle crystals

Abstract

The occurrence of the second peak (SP) on the dc magnetization curves of iron pnictide and chalcogenide single crystals (the 'fishtail' effect) has been interpreted in surprisingly different ways, involving, for example, a thermally induced square-to-rhombic vortex lattice transition, a crossover between single vortex pinning in the low magnetic field range and pinning of interacting vortices at higher fields, or has been treated similarly to the peak effect close to the upper critical magnetic field. Here we show that the SP in FeSe 1−x Te x single crystals is related to the well documented order-disorder transition in the vortex system, and its evolution in the low-temperature T domain is described by a dynamic energy balance relation. The main argument supporting this approach is the observed strong increase of the field for the onset of the SP with decreasing T down to 2 K, with an inflection-like point located between 3 and 4 K, in agreement with the two-band superconductivity reported for FeSe 1−x Te x .

Second magnetization peak effect, vortex dynamics and flux pinning in 112-type superconductor Ca0.8La0.2Fe1−xCoxAs2

“…In low temperature region (large J ), the obtained μ ( ∼ 1.21) value resides between that of single-vortex ( μ  = 1/7) (or intermediate-bundle) and small-bundle regimes, indicating contributions from different pinning types. The μ value in our experiment is close to many other IBSs1220214244. In contrast, in high temperature (low J ) region, the obtained slope is ~  − 0.52, which is in good agreement with predicted p  = −0.5 in plastic-creep theory4.…”

“…In cuprates, different vortex dynamical mechanisms including crossover from elastic to plastic (E-P) vortex creep4, vortex order-disorder phase transition16, vortex lattice structural phase transition (VL)17, surface barriers18, etc., were proposed in SMP interpretation. In iron pnictides, SMP has been observed in all of the four main systems, 1111-type SmFeAs(O, F) and NdFeAs(O, F)819, 122-type (Ba, K)Fe 2 As 2 and Ba(Fe, Co) 2 As 2 912, 111-type LiFeAs14, and 11-type Fe 1 +  x (Te, Se)13152021. However, similar as cuprates, different explanations were proposed781419.…”

Vortex dynamics and second magnetization peak in PrFeAsO0.60F0.12 superconductor

“…8(a)). The location of this inflection point is found to be in good agreement with the results obtained for λ(T ) in underdoped PrFeAsO 1−y single crystal [59] and following Miu et al [57,58] we associate this feature with the T dependence of the superfluid density (n s ∝ λ −2 ) in the case of two-band superconductivity.…”

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

“…8 (a), (b)). These µ values are different than the predicted ones, as found in other studies on several superconductors [24,27,33,[50][51][52]. Similarly, values of he exponent (p) at higher temperature side (low J) is also found to be different than the predicted value for plastic creep (p = 0.5) [5,32].…”