Exponential field dependence of critical current density of underdoped (La 1− xSr x) 2CuO 4 single crystals

Abstract

The magnetic-hysteresis curves up to ±9 T of single-crystalline ((La 1− x Sr x ) 2CuO 4 ( x ≤ 0.061) in the under-doped composition were examined with respect to the dependence of the critical current density J c on the internal magnetic-flux distribution B. The exponential model ( J c α exp(− B/ B 0)) could best reproduce the hysteresis curves obtained over a wide field range, while neither the modified Bean model nor the modified Irie-Yamafuji model ( J c( B) = J c0(| B|/ B c2) γ−1 (1 − | B|/ B c2) δ ) could do so. The exponential dependence of J c on B was discussed in terms of the available models. It was also shown that J c obtained by fitting to the exponential model did not follow the Kramers scaling law.