Phase separation of bilayered perovskite manganite (La1-xGdx)4/3Sr5/3Mn2 O7 (x=0, 0.05)

La1-xGdx)4/3Sr5/3Mn2 O7 (x=0, 0.05) polycrystalline samples have been prepared by solid state reaction method, and the phase separation phenomena in this samples are investigated by measuring the magnetization-temperature (M-T) curve, electron spin resonance (ESR) curve and resistivity-temperature (-T) curve. For both samples, experimental results suggest there exists competition between ferromagnetic and antiferromagnetic interactions in low temperature range, which reflects a characteristic of cluster spin glass. A Griffiths-like phase is observed in temperature ranges 125375 K and 100375 K for x=0 sample and x=0.05 sample, respectively. It is found that doping contributes to the decrease of three-dimensional long-range ferromagnetic ordering temperature (from Tc03D 125 K for x=0 to Tc13D 100 K for x=0.05), but has no obvious effect on the Griffiths-like temperature (TG 375 K). Above TG 375 K, a pure paramagnetic phase appears in both samples. The -T curves reveal two insulator-metal transitions in the entire temperature range for x=0 sample, which is caused by coexistence of the two phases in perovskite manganese oxides. For x=0.05 sample, however, there exhibits a single insulator-metal transition, indicating that doping can hinder the coexistence phenomenon. It can be seen from the fitted -T curves that the electron conduction mechanism in high temperature range is in accordance with the three-dimensional variable range of hopping conduction.