CRITICAL-CURRENT DENSITY OF A SAMPLE OF MELT GROWN YBCO

The critical current density (J(c)) of a sample of YBCO prepared by Melt Grown (MG) process has been studied as a function of magnetic field using a magnetization technique. The micrographic investigation shows well aligned grains in this material. The magnetic hysteresis measurements were done using a MPMS SQUID magnetometer up to the fields of 5.5 Tesla. The J(c) was estimated from the remanent magnetization using Bean model. The validity of a Bean model has been justified for its application in obtaining J(c) by the presence of only one kind of low field hysteresis loops. (Absence of two kinds of low field hysteresis loops corresponding to inter and intra grain magnetizations). This is a valid proof that the weak links are greatly eliminated in these samples prepared by MG process. The J(c) behaviour as a function of magnetic field has a two components, a rapidly decaying exponential function of field and other component that predominates at higher fields. This could be explained on the basis of a model that the sample contains two phases of superconductors, one having a low H(c2) become normal at fairly medium fields of the order of few Kilo Gauss will act as pinning centres for the other phase having higher H(c2) and hence higher J(c) at high fields.