Absence of a Bulk Meissner State in RuSr2GdCu2O8

We have systematically investigated the magnetic, electrical, and structural properties of RuSr2GdCu2O8, in which a long-range ferromagnetic order and superconductivity have been previously reported to coexist. Based on the reversible magnetization results, we conclude that the bulk Meissner state does not exist in this compound and that the condensation energy associated with superconductivity is negligible. The absence of a bulk Meissner state and the superconductivity detected are thus attributed to the possible appearance of a sponge-like crypto-superconducting fine structure in RuSr2GdCu2O8 samples that are found to be chemically homogeneous to 1-2 mu m and electrically uniform to \~ 10 mu m across the sample.