Observations and model of a new ac-loss valley in a YBCO superconductor

Abstract

We report on measurements of the ac susceptibility of sinteredYBCO pellets, with ZnO added, as a function of temperatureT, for several different ac magnetic field amplitudes,Hac, in the presence of static bias magnetic fieldHb directedalong Hac. Foreach choice of Hac, the imaginary part of the ac susceptibility versusT traces a peak,denoted χ′′max, centred at atemperature denoted Tmax. We find that χ′′max versus both Hac and Tmax traces a valley. Calculations of hysteresis losses, exploiting the critical state model where the critical currentdensity jc = α(T)/Bn, reproduce the experimental data quite well.