Measurement of magnetic properties in a melt cast Bi-Ca-Sr-Cu-O superconductor

Magnetic measurements were made to examine the superconducting properties of a crystalline chunk, consisting of many small crystals, prepared by casting from the oxide melt with a starting composition of Bi3Ca2Sr2Cu3Ox. AC susceptibility revealed an onset temperature of 82 K and a transition width of ∼ 10 K. Hysteresis loops at 70 K showed a very small hysteresis, indicating a low density of effective flux pinning sites at this temperature, similar to the behavior observed for some superconducting samples of the Bi-Ca-Sr-Cu-O system prepared by other techniques. However, the magnetization at 10 K showed no hysteresis for fields greater than ∼ 3.5 kOe, a much smaller value than we have previously observed for other samples of this material regardless of preparation method, or for any other material with a Tc greater than 70 K. This critical field for flux depinning, Hcp, varies with temperature as Hcp - 4980(1-t)2.5, where t is T/Tc