Different effects of Fe and Ga doping on Tc between the Bi2201 system and the La214 system

Single-phase samples Bi1.8Pb0.2Sr1.6 + xLa0.4-xCu1-xMxOy and La1.85-xSr0.15 + x Cu1-xMxOy (M = Fe3+,Ga3+) were synthesized by the solid state reaction method. The crystal structure, transport properties and spin dynamics were investigated by means of x-ray diffraction (XRD), resistivity, thermoelectric power (TEP) measurement and the electron spin resonance (ESR) spectrum. It is found that Fe doping suppresses Tc more effectively in the La214 system than in the Bi2201 system, while Ga doping shows a similar effect on Tc in both the Bi2201 system and the La214 system. The different effects of Fe doping on the broad peaks in S(T)-T curves between the La214 system and the Bi2201 system are clearly observed, while Ga doping shows a similar influence on the broad peaks in S(T)-T curves. ESR results show that a strong ESR signal from Fe3+ spins was detected in the La214 system, but no ESR signals were observed in the Bi2201 system. It is suggested that there exist different spin dynamic behaviours between the two systems. The superconductivity and transport properties are discussed based on these experimental results.