Transport properties and Raman spectra of Ru1−x AlxSr2GdCu2O8 (Al-doped Ru-1212) with x=0, 0.05, 0.1 and 0.15 have been investigated. The superconducting transition temperature of the Al-doped Ru1212 increases with increasing Al content up to 10%, and then decreases with increasing Al content. The observed result seems to indicate that excess holes induced by Al doping could transfer from RuO2 plane to CuO2 plane through apical oxygen for 0<x<0.1. Whereas for x>0.1, the holes might be trapped or localized in the RuO2 plane due to a local disorder induced by Al doping. The temperature dependence of the critical field can be fitted as H c2(T)=34(1−T/Tc)4.8, suggesting that the vortex dynamics of Ru-1212 might be intrinsically different from that of the other high-T c cuprates. The largest magnetoresistance (MR) of the Al-doped Ru-1212 occurs around magnetic ordering temperature, indicating that the exchange interaction between the carriers in CuO2 planes and the spins in RuO2 planes dominates the magneto-transport properties of the Ru-1212 system. The peak position of the 150 cm−1 involving Cu vibration along the c-axis hardly changes as x increases. It reveals that Al doesn't occupy Cu site. A new Raman active mode around 550 cm−1 observed in the Al-doped compounds might be attributed to doping-induced A1g -like apical oxygen mode.
Journal of low temperature physics 131(3-4), pp.659-664