Vacancy induced spin state transition in La0.7Sr0.3-x□xCoO3 (0≤x≤0.2) cobaltites

Effects of vacancy doping in polycrystalline La0.7Sr0.3-xxCoO3 (0≤x≤0.2) cobaltites on their crystal structure, magnetic and transport properties have been systematically investigated. With increasing Sr deficiency, the antiferromagnetic superexchange is promoted at the expense of double exchange between ferromagnetic clusters, with cluster-glass state being prevailing, which is due to the gradual decrease of A site ionic radius as well as more intrinsic disorder. As x is increased beyond 0.1, it is found that the Co—O bond length shrinks remarkably. This tends to enlarge the crystal-field splitting energy and most Co3+ ions are inclined to prefer low spin states. The ground state shows superparamagnetic-like features, thus giving rise to metal-insulator transition.