The magnetization of single-phased Ru-1212, which possesses a ferromagnetic transition at 133 K and a super-conducting transition around 30 K, was measured. No bulk Meissner effect can be detected down to 2 K and 0.2 Oe, although both a diamagnetic susceptibility -4πχ ≥ 1 in the zero-field-cooled mode and a small M-drop in the field-cooled mode appear. Almost the same reversible magnetizations in Ru-1212 and Zn-doped Ru-1212 further suggest that the superconducting state of Ru-1212 is severely modified by the coexistence of ferromagnetism. $ 2000 Elsevier Science B.V All rights reserved.
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