Phase separation and abnormal transport behaviours in La_0.7-xGd_xSr_0.3MnO₃ system

The magnetic and transport behaviours of the La_0.7-xGd_xSr_0.3MnO_3 (0≤x≤0.70) system are investigated. The experimental results indicate that with increasing Gd doping content, the magnetism of the system changes from the long-range ferromagnetic order state to the cluster-spin glass state, then to the antiferromagnetic (AFM) state. It is interesting that the phase separation appears at x=0.30 and 0.40 and disappears for x≥0.50 where the AFM state occurs. At high doping content, the transport behaviours exhibit abnormality, e.g. there are two temperature ranges in which the \rho－T curves can be well fitted by a variable-range hopping (VRH) model. We suggest that the VRH does not come from the hopping of carriers between clusters, but from the different magnetic backgrounds in the clusters.