SUCCESSIVE TRANSITIONS IN YBa2Cu4O8 CERAMIC SUPERCONDUCTOR BY DC AND AC MAGNETIC MEASUREMENTS

Abstract
Ordering of a YBa 2 Cu 4 O 8 ceramic superconductor is investigated by DC and AC magnetic measurements. Successive transitions are found at two temperatures T c1 (= 80 K ) and T c2 (= 30 K ) and identified as those from the normal state into a superconductive order inside cach grain with inter-grain disorder and from the intermediate state into the inter-grain(bulk) superconductive state over the whole sample, respectively. Linear and nonlinear responses to AC magnetic excitation at very low frequencies revealed a remarkable anomaly around T c2 and T c1 , reflecting the critical fluctuation at the transitions.

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