Observations of a hysteresis loss valley in yttrium barium copper oxide superconductors

Abstract

We present measurements of the ac susceptibility of sintered yttrium barium copper oxide pellets prepared by a melt processed solid state reaction method, with different amounts of ZnO added. The measurements were performed versus temperature T for several different ac magnetic field amplitudes Hac in the presence of static bias magnetic fields Hb directed along Hac. For all our samples, for each choice of Hac, the imaginary part of the ac susceptibility versus T traces a peak, denoted by χ″max, centered at a temperature denoted by Tmax.We also find that plots of the values of χ″max vs Hac and of χ″max vs Tmax generate curves that display a valley. Calculations of hysteresis losses, exploiting a critical-state model where the critical current density jc=α(T)∕Bn, reproduce the experimental data quite well.