Flux pinning properties in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ single crystals and the effect of introducing nano-size MgO particles

The pinning properties in Bi(2212) single crystals prepared by the large temperature-gradient technique are reported in comparison with that of 5% MgO nano-size particle-added Bi(2212) crystals. We studied the scaling of volume pinning force density F/sub p/ to the irreversibility field B/sub irr/ as the scaling field parallel to the c-axis for these Bi(2212) crystals at low temperature from 18 K to 30 K. It was found that for the MgO added-crystals the normalized F/sub p/ was scaled to temperature but for a single crystal no scaling was observed for the irreversible field B/sub irr/ obtained from the field dependence of the irreversibility temperature. When a field B* which gives one percent of the maximum pinning force density F/sub pmax/ was substituted for B/sub irr/, F/sub p//F/sub pmax/ in single crystal scaled with B/B*. We discussed the origin of disagreement between the irreversibility field B/sub irr/ and field B* in a single crystal and the effect of the MgO addition to the Bi(2212) crystal. Critical current of the Bi(2212) crystal in low temperature region could be improved by the 5% addition of the MgO nano-size particles.