Crystal Structure and Curie Temperature of Sm2Fe17—yGayCx

Abstract

Magnetic relaxation and flux pinning behaviors have been investigated on the c-axis oriented [YBa2Cu3O7 (24 Angstrom)/PrBa2Cu3O7 (24 Angstrom)](12) multilayers in the perpendicular magnetic fields (H parallel to c-axis) up to 2 T. The critical current density, J(c), value is of the order of 10(6) A/cm(2) in the investigated temperature range and at magnetic field H approximate to 0. The proximate logarithmic dependence of magnetization on time is observed in this multilayers. The magnetic relaxation rate Q = dM/dln t decreases monotonically with increasing temperature. The normalized magnetic relaxation rate S shows a maximum value in S-T curves at low magnetic fields. The behaviors of Q and S are found to be strongly dependent on the magnetic fields. A scaling form of vortex activation energy, U-eff(J, T) = U(i)G(T)F(J(i)/J) was used to analyze the flux pinning behavior at the given magnetic field. Here U-i and J(i) are scaling constants of activation energy and current density, respectively, and G(T) is empirically chosen as G(T) = (1-(T/T-r)(2))(3/2) With T-r being the irreversibility temperature. The current density dependence of U-eff is in agreement with the prediction of collective-pinning theory. The possible pinning mechanisms are proposed. (C) 1997 Elsevier Science B.V.