Irreversibility line of Ba 1-xK xFe 2As 2 (T c = 36.9 K) superconductor studied with ac-susceptibility measurements Article

cited authors

  • Pissas, M; Zeibekis, M; Stamopoulos, D; Wang, C; Ma, Y

fiu authors

abstract

  • We have studied the phase diagram of a Ba 1-xK xFe 2As 2 (T c = 36.9 K) single crystal superconductor by employing ac-susceptibility measurements, both as a function of temperature for constant external magnetic field and of magnetic dc-field for constant temperature for angles Θ = ∠(H, c-axis) = 0°, 30°, 45°, 60°, 75° and 90°, between the c-axis and the magnetic field. The irreversibility lines (H irr(T, Θ)) are estimated from the onset of non-zero values of the amplitude of the third harmonic susceptibility. H irr-lines for all the studied angles can be reproduced from the equation H irr = H 0(Θ)(1 - T/T c) n, with n ≈ 4/3. From the angular dependence of H 0(Θ) parameter, we estimated the anisotropy of the irreversibility lines. In the temperature interval [35, T c] the anisotropy parameter was estimated γ=Hirrab/Hirrc=2.2±0.1. The measurements of the real part of the fundamental (first harmonic) ac-susceptibility χ′(T) for constant temperature as a function of dc-magnetic field revealed, for high values of the ac-field amplitude, a second peak in the critical current. The second peak line is located far from H irr-line and exists up to T c. Although the particular sample has high critical densities, contrary to the predictions of the Bean's model, the maximum of the imaginary part of the fundamental ac-susceptibility χ″ exhibits lower values. This behavior could be explained by assuming a reversible motion of the flux lines around the pinning centers for low values of the ac-magnetic field amplitude. © 2012 Elsevier B.V. All rights reserved.

publication date

  • June 1, 2012

Digital Object Identifier (DOI)

start page

  • 68

end page

  • 72

volume

  • 476