Magnetic and transport properties of $\mathrm{Co}{\mathrm{Sr}}_2{\mathrm{Y}}_{1-x}{\mathrm{Ca}}_x{\mathrm{Cu}}_2{\mathrm{O}}_7$ $(x=0–0.4)$ system have been investigated. A broad maximum in the $M\left(T\right)$ curve, indicative of low-dimensional antiferromagnetic ordering originated from $\mathrm{Co}{\mathrm{O}}_{1+\delta }$ layers, is observed in the Ca-free sample. With increasing as Ca doping level up to 0.2, the $M\left(T\right)$ curve remains almost unchanged, while resistivity is reduced by three orders. A 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 $M\left(T\right)$ is much lower 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 $\mathrm{Co}{\mathrm{O}}_{1+\delta }$ layers are involved in charge transport, in addition to conducting $\mathrm{Cu}{\mathrm{O}}_2$ planes to interpret the correlation between magnetism and charge transport. X-ray photoelectron spectroscopy studies give additional evidence of the the transfer of the holes into the $\mathrm{Co}{\mathrm{O}}_{1+\delta }$ charge reservoir.

• Received 2 January 2004

DOI:https://doi.org/10.1103/PhysRevB.70.054520