Electrical resistivity and magnetic susceptibility inBiCaSrCu2Oy

Electrical-resistivity and static magnetic-susceptibility measurements were performed on a new type of high-$T_c$ superconductor $\mathrm{Bi}\mathrm{Ca}\mathrm{Sr}{\mathrm{Cu}}_2{\mathrm{O}}_y$ ($y\cong 6.4$) in the temperature range $70 \mathrm{K}\le T\le 310 \mathrm{K}$. The stoichiometry of this compound is described as BiCa${\mathrm{S}\mathrm{r}\left[{\mathrm{Cu}}_{0.1}^{2+}{\mathrm{Cu}}_{0.9}^{3+}\right]}_2$ ${\mathrm{O}}_{6.4}$. The electrical resistivity shows superconductivity below $T_c=73.9\mathrm{}$ K, and undergoes a steplike change at 110 K, suggesting a high-$T_c$ phase. The linear temperature dependence of the resistivity is observed in the temperature range $130 \mathrm{K}\le T\le 254 \mathrm{K}$. The susceptibility shows a Curie-Weiss behavior with $\Theta =-113.1\mathrm{}$ K and $P_{\mathrm{eff}}=0.56\mathrm{}$ ${\mathrm{\mu }}_{\mathrm{B}}$/mol Cu, because of antiferromagnetic exchange interaction between localized ${\mathrm{Cu}}^{2+}$ spins. From a temperature-independent susceptibility, the electronic specific heat ${\gamma }_{\mathrm{el}}$ and the density of states $D\left(E_F\right)$ are determined as ${\gamma }_{\mathrm{el}}=12.0\mathrm{}$ mJ/mol Cu ${\mathrm{K}}^2$ and $D\left(E_F\right)=5.09\mathrm{}$ states/eV Cu atom.