Fishtail shape in the magnetic hysteresis loop for superconductors:Interplay between different pinning mechanisms

Abstract

The scaling and relaxation behavior around the fishtail minimum is studied in detail in a wide temperature range ͑3-70 K͒ on DyBa 2 Cu 3 O 7Ϫ␦ single crystals exhibiting a pronounced fishtail effect. Magnetic hysteresis loops ͑MHL's͒ normalized with respect to the height and position of the fishtail maximum fall on a universal curve which form can be derived from the phenomenological model of a thermally activated flux creep proposed by Perkins et al. ͓Phys. Rev. B 51, 8513 ͑1995͔͒. This universal curve tends at low fields towards zero. At low temperatures, the drop of j s at low fields is usually masked by a wide central peak. By subtracting the universal curve from the experimental j s (B) data we separate the contribution of the central peak. It has a simple, exponentially decaying field dependence. This implies that the fishtail minimum at low fields might be understood as a result of an overlapping of two contributions originating from separate pinning mechanisms: one active mainly at high fields and dying away with B going to zero and another one ͑responsible for the central peak of the MHL͒ vanishing rapidly with increasing field. This concept is also supported by relaxation experiments. These experiments confirm that the shape of MHL's is given by a dynamic equilibrium between the induction, pinning, and relaxation processes. ͓S0163-1829͑97͒05305-8͔

Peak effect, vortex-lattice melting line, and order-disorder transition in conventional and high-Tcsuperconductors

“…38-40. This magnitude, as well as the correlation functions (8) and (14), depends on the elastic moduli of the lattice. However, in deriving Eqs.…”

“…[1][2][3][4][5] In the high-T c YBaCuO crystals, the line of the maximum critical current density, H p (T ), frequently lies essentially below the irreversibility line in the H − T plane, [6][7][8][9] and in sufficiently perfect crystals it exhibits nonmonotonic behavior with temperature. [10][11][12][13][14][15][16] In these perfect crystals the line of maximum current density approaches the flux-line melting line, H m (T ), approximately at the so-called upper critical point 17 at which the melting line terminates.…”

Effect of mesoscopic inhomogeneities on the critical current of bulk melt-textured YBCO

“…Perkins et al [24][25], Tirsa et al [26], based on the theory of collective vortex pinning, developed a method for generalization of experimental results for J c (B,T) for a considerable number of different Re(123) using only two parameters which govern the vortex pinning condition. But the physical essence of these parameters, their dependence on the real structure of RE(123) are not clear yet.…”

Modelling of Critical Current Density of Sintered Ag Added Bulk MgB2

“…Up to now, several models have been proposed based on thermodynamic and some phenomenological considerations. For bulk high T c superconductors with an intensive thermally activated flux motion Perkins et al [28,29] and Jirsa et al proposed a model enabling to fit the secondary peak on the critical current density as a function of magnetic field [30]. It worked well for NEG-123 and Gd-123 bulks and for Eu-123 thick films [14].…”