Detailed Physical Characterizations of Cu-rich and Ru-poor (RuCu)SrYCuO.

The optimized nominal composition, (RuCu) SrYCuO sample, has been prepared through high-pressure and high-temperature solid-state densification method. The obtained material has been studied by X-ray (laboratory) diffraction powder technique, magnetization and detailed magneto-transport measurements. The title compound indicates bulk magneto-superconducting properties under field strengths of H=10, 100, 500 and 1000 Oe. It shows diamagnetic transition at T=54, 38, 20 and 8 K for H=10, 100, 500 and 1000 Oe, respectively, in the zero-field-cooled susceptibility measurements. The high-field ( H=5 and 10 kOe) molar susceptibility measurements show sharp ferromagnetic transition at ∼150 K with reduced molar susceptibility values. The various field dependence of magnetization, M( H), isotherm curves recorded at constant temperatures (5, 10, 25, 50, 100 and 150 K) indicate ferromagnetic saturation, whereas the MH curves measured at 200 and 300 K conditions reveal the paramagnetic state of the compound. Though the sample showed onset transition temperature, $T_{\mathrm{c}}^{\mathrm{onset}}$, at ∼34 K under different field strengths ( H=0, 10, 30, 50, 70 and 90 kOe), no $T_{\mathrm{c}}^{R=0}$ is seen down to 2 K. Even under relatively low applied field (Δ H=10 kOe) the title compound shows large negative magnetoresistance ( MR) of about 68% at 2 K and increases with increasing the field strength up to Δ H=90 kOe ( MR=77% at 2 K). This value is amazing and probably higher than other 1212 type ruthenocuprates. The title compound which shows little negative MR (about 1%) in the high temperature regions (125-300 K) is not affected much by different field strengths. Among the different fixed temperature MR( H) isotherms, the MR( H) curve measured at 5 K shows maximum negative MR of about 47% at 90 kOe compared to other four ( T=50, 100, 200 and 300 K) MR( H) curves. [ABSTRACT FROM AUTHOR]