Magnetic and superconducting properties of RuSr2GdCu2O8; the effect of synthesis

High-pressure oxygen synthesis has been found to promote the formation of t he phase pure RuSr2GdCu2O8 superconductor. By changing the oxygenation cond itions we were able to successfully change T-c(on) in the range of 25-35K. The larger diamagnetic response was always observed for samples with higher T-c. Large zero-field-cooled - field-cooled hysteresis in de magnetization exists below the temperature of magnetic ordering of the Ru sublattice (T= 131 K). A low temperature anomaly in de magnetization has been observed at the temperature corresponding to the onset of the superconducting transitio n as determined by the ac susceptibility.