Magnetic and transport properties in Gd1-xSrxCoO3-δ (x = 0.10-0.70)

Magnetic and transport properties of polycrystalline Gd 1-x Sr x CoO 3-δ (x = 0.10-0.70) annealed under the oxygen pressure of 165 atm at 500 °C are systematically investigated. Cluster-glass behavior is observed in the low doping range, while a ferromagnetic transition occurs at the high doping level. Transport measurements indicate insulator-like behavior for the samples with x ≤ 0.30, an insulator-metal transition around x = 0.35, and metallic behavior for higher x samples. However, the large oxygen deficiency leads to a re-entrance of insulator-like state for the samples with x ≥ 0.60. The annealing procedure under the high oxygen pressure at high temperature can diminish the oxygen deficiency and leads to restoration of the metallic state. The small radius of the Gd 3+ ion results in less conduction and lower T c compared to those of La 1-x Sr x CoO 3 and Nd 1-x Sr x CoO 3 as a result of the large structural distortion and the stability of the low-spin state.