Unusual Field-Dependence of the Intragrain Superconductive Transition in RuSr2EuCu2O8

A narrow intragrain phase-lock transition was observed in RuSr2EuCu2O8 under a magnetic field H up to a few Tesla. The corresponding transition temperature, T2, decreases rapidly (about 100 K/T at low fields) with H indicating that the grains of RuSr2EuCu2O8 behave like a Josephson-junction-array instead of a homogeneous bulk superconductor. Our data suggest that the bulk superconducting transition may occur on a length scale well below the grain size of 2 to 6 micrometer.