Lattice effects on magnetic and transport properties in La site doping La0.67Sr0.33CoO3

The lattice effects on the magnetic and transport properties in La0.67-xGdxSr0.33CoO3 series are studied. The system exhibits a rhombohedrally distorted perovskite structure for x<0.30 and an orthorhombic structure for x>0.30. The introduction of smaller Gd3+ ions leads to an enhanced mismatch between the LaO layer and the CoO2 layer and a decrease of the tolerance factor t. The spin-state of trivalent Co ion is converted to low-spin state with the decrease of CoO bond length. The doping of Gd3+ drives the system from the cluster-glass state to the spin-glass state and progressively decreases the Curie temperature. At high Gd3+ doping content, an interesting negative magnetoresistance occurs at low temperature.