HIGH-FIELD MAGNETIZATION STUDY OF YBA2CU4O8

We present the results of experimental studies of magnetic hysteresis in YBa2Cu4O8 superconductor. The variation of magnetic critical curren t density with magnetic field and temperature is presented. The result s are analyzed on the basis of Bean's critical state model and its var ious extensions. From our experimental results it is evident that J(c) (H) follows a power law in the field region between H(I) (field of ful l penetration) and H(II) (field where the remnant magnetization satura tes). J(c)(T) varies exponentially in a limited temperature and field region. From the present results we conjecture that the magnetic criti cal current density follows the relation, J(c)(H,T) = K(H/H(I))-n exp( -T/T0) in the field region between H(I) and H(II) and temperature belo w T(c)/2.