Granularity and intragrain penetration depth in RuSr2GdCu2O8

The multi-stage transition of RuSr2GdCu2O8 (Ru1212) ceramic samples was investigated. An intergrain phase-lock temperature of T-2 is identified around 10-30 K. Slightly above T-2, however, an isolated Ru1212 grain still behaves as a Josephson-junction array of superconductive nano-domains, which are phase-locked below an interdomain phase-lock temperature (intragrain transition-temperature) of T-1 approximate to 33-40 K. The intragrain penetration depth lambda (1) was subsequently deduced from the ac susceptibility x' of powders with different particle-size d (0.3 less than or equal to d less than or equal to 10 mum in this work) between T-1 and T-2. The sample-dependent lambda (1) approximate to 2.5-6 mum so obtained is extremely long, and bears a systematic correlation with the T-1 observed. A phase-separation model was proposed to interpret the data. (C) 2001 Published by Elsevier Science B.V.