Low frequency AC absorption in YBa2[(CuO)(1-x)(MS)(x)](3)O4-delta (M = Fe (x=0,01, 0,02, 0,05), Ni (x=0.01) or Zn (x=0.02, 0.05)) samples

We report and analyze AC susceptibility data of polycrystalline high-T-c su perconductors. The purpose of these investigations is to study the effect o f doping YBa2Cu3O7-delta with M = Fe, Ni or Zn sulfides on the low frequenc y AC losses of these materials. We measured the AC susceptibility of sinter ed YBa2[(CuO)(1-chi)(MS)(chi)](3)O4-delta pellets as a function of temperat ure acid AC magnetic-field amplitude and frequency. The imaginary part of t he AC susceptibility (chi ") in terms of temperature and magnetic field int ensity show remarkable characteristics. As the applied magnetic field inten sity is increased, the three loss peaks (intergranular, intragranular, intr insic) that can be observed, show shifts to lower temperatures. The intergr anular and intragranular peak shift (because of doping and magnetic held va riation) is explained by the Muller critical state model and shows hysteret ic effect. The intrinsic peak shift follows the T-c changes and shows no hy steretic effect. (C) 2001 Elsevier Science B.V. All rights reserved.