Increase in the magnetization loop width in the Ba0.6K0.4BiO3 superconductor: Possible manifestation of phase separation

Use of a Sigmoid Function to Describe Second Peak in Magnetization Loops

“…The peak in the j peak c (B) dependence is accompanied by a decrease of l s values such that l s,2 /l s,1 ≈ j c,1 /j c,2 . This relation is observed in asymmetric magnetization loops with the peak effect 14,[24][25][26][27] . The depth of the equilibrium region during the order-disorder transition changes as…”

“…The electromagnetic granularity may emerge due to phase separation in some superconductors. The phase separation into the insulating and superconducting regions is observed in Ba 0.6 K 0.4 BiO 3 superconductor in the range of fields and temperatures overlapping with the peak effect 14 . A network consisting from non-superconducting and superconducting clusters is formed in the sample due to the phase separation.…”

“…Earlier, the critical state model [8][9][10][11][12] and the extended critical state model 13,14 were used to describe the peak effect without considering underlying mechanisms. In these works nonmonotonic dependencies of the critical current density j c on magnetic field B are suggested.…”

Analysis of Superconductor Magnetization Hysteresis

“…The demagnetization factor can distort the value of x. Additional diamagnetic [5] / paramagnetic [6,7] phases in a sample tilt the magnetization hysteresis clockwise / anticlockwise. Coexistence of superconducting and ferromagnetic phases in a sample gives a composite hysteresis [8].…”

“…These j c values obtained are the critical current density averaged on the cross-section perpendicular to the external magnetic field H. Then the field dependence of the pinning force F p (H) = µ 0 Hj c (H) is plotted that allows to find the maximal pinning field and H irr also. If the second peak (fishtail, peak effect) is noticeable on a magnetization hysteresis and on field dependencies of j c and F p than the peak position and its temperature evolution contain information about the vortex lattice transition or the phase separation in superconductor [5]. Fig.…”