Anisotropic properties of the anomalous second peak in the magnetization curves and the irreversibility field of YBa 2Cu 3O y (6.6 ≤ y ≤ 6.9) single crystals

Abstract

Anisotropic properties of the anomalous second peak in the magnetization curves and the irreversibility field have been investigated by magnetic measurement for YBa 2Cu 3O 7 (6.6 ≤ y ≤ 6.9) single crystals in magnetic fields up to 55 kOe. The angular dependence of the magnetic field H p at which the second peak appears is well described by the Ginzburg-Landau effective-mass model. This behavior results from the anisotropic vortex structure dominated by the effective mass of superconducting electrons. However, the anisotropic behavior of the irreversibility field H irr is given by an extended expression, H irr ln H irr ∞ 1/( cos 2θ + γ −2 sin 2θ) 1 2 , which is proposed by taking account of the influence of the flux creep on the irreversibility field. The anisotropic parameter γ is consistently estimated from the angular dependence of both characteristic fields of H p and H irr. The γ value increases with decreasing oxygen content indicating the suppression of the interlayer coupling between CuO 2 superconducting layers by reducing oxygen.