Field dependence of the intragrain superconductive transition in RuSr 2 EuCu 2 O 8

A narrow intragrain phase-lock transition was observed in ${\mathrm{RuSr}}_{2}{\mathrm{EuCu}}_{2}{\mathrm{O}}_{8}$ under a magnetic field H up to a few Tesla. The corresponding transition temperature ${T}_{2}$ decreases rapidly $(\ensuremath{\approx}100 \mathrm{K}/\mathrm{T}$ at low fields) with H, indicating that the grains of ${\mathrm{RuSr}}_{2}{\mathrm{EuCu}}_{2}{\mathrm{O}}_{8}$ behave unlike a homogeneous bulk superconductor. Our data suggest that the bulk superconducting transition may occur on a length scale well below the grain size $2\char21{}6 \ensuremath{\mu}\mathrm{m}.$