Scaling of nonlinear complex susceptibility applied to the study of type-II superconductors

Different chi measurements can be collapsed into a single universal curve if plotted against the scaling variable h(omega (overbar)/omega)(1/sigma) or, more generally, h/Jd, where J(T, B, omega) is a frequency dependent shielding current density, d is the sample half-width and h is the AC field amplitude. We have tested these scaling laws for two Nb samples, one melt textured YBCO sample, and one Er123 single crystal. Further, we found that J(T,B, omega) for Er123 displays a behavior closely related to the second magnetization peak (fishtail effect), observed in M x H curves. Our results are satisfactorily interpreted in terms of vortex dynamic models. (C) 2001 Elsevier Science B.V. All rights reserved.