Magnetic and Transport Properties in CoSr₂Y₁₋ₓCaₓCu₂O₇ (x=0 0.4)

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Magnetic and transport properties of Co Sr₂ Y₁₋ₓ Caₓ Cu₂ O₇ (x=0 0.4) system have been investigated. A broad maximum in M(T) curve, indicative of low-dimensional antiferromagnetic ordering originated from CoO₁₊δ layers, is observed in Ca-free sample. With increasing Ca doping level up to 0.2, the M(T) curve remains almost unchanged, while resistivity is reduced by three orders. Higher Ca doping level leads to a drastic change of magnetic properties. In comparison with the samples with x=0.0 0.2, the temperature corresponding to the maximum of M(T) is much lowered for the sample x=0.3. The sample x=0.4 shows a small kink instead of a broad maximum and a weak ferromagnetic feature. The electrical transport behavior is found to be closely related to magnetic properties for the sample x=0.2, 0.25, 0.3, 0.4. It suggests that CoO₁₊δ layers are involved in charge transport in addition to conducting CuO₂ planes to interpret the correlation between magnetism and charge transport. X-ray photoelectron spectroscopy studies give an additional evidence of the the transfer of the holes into the CoO₁₊δ charge reservoir.