Critical current density and flux pinning characteristics of powdered MgB2 specimens

Field and temperature dependence of magnetization and also time dependent magnetization (flux creep) of powdered MgB2 specimens have been measured by using a SQUID magnetometer in the temperature range of 4.5⩽T⩽37 K and under the field up to 1 T. Scaling plots of normalized pinning force density Fp/Fpmax as a function of normalized flux density B/Bmax in the temperature range of 25⩽T⩽37 K showed that a two dimensional pinning is dominant for the flux pinning of the specimens. Another distinct feature is that a linear reduction of Jc with increasing temperature at temperatures lower than 30 K and a quadratic decrease at higher temperatures than 35 K have been observed.