Magnetization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ high T/sub c/ superconductor

Magnetization data are reported on a sintered YBa/sub 2/Cu/sub 3/O/sub 7-x/ sample and a powdered one, both at liquid helium and nitrogen temperatures. The results are consistent with the weakly coupled superconducting grains model. Loss values at very low AC field are reported. Critical current densities within the grains are deduced and turn out to be in excess of 10/sup 6/ A/cm/sup 2/ at 4.2 K and 1 T.<
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