La_(0.7)Sr_(0.3-x)Ⅱ_xCoO_3(0≤x≤0.2)钴氧化物中锶空位诱导的自旋态转变效应

Vacancy induced spin state transition in La_(0.7)Sr_(0.3-x)Ⅱ_ xCoO_3(0≤x≤0.2) cobaltites

研究了锶空位对La0.7Sr0.3-xⅡxCoO3(0≤x≤0.2)多晶钴氧化物结构、磁性和输运性质的影响.结果表明:随着锶空位浓度x的增大,A位阳离子无序度增大,导致铁磁双交换作用减弱及反铁磁超交换作用增强,两者相互竞争,出现团簇自旋玻璃态;空位浓度超过10%后,Co—O键长迅速减小,导致晶体场劈裂能加大,大部分三价钴离子以低自旋态出现,系统基态为类超顺磁态,同时样品发生金属-绝缘体相变.

Effects of vacancy doping in polycrystalline La0.7Sr0.3-x□xCoO3 （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 Co^3＋ ions are inclined to prefer low spin states. The ground state shows superparamagnetic-like features, thus giving rise to metal-insulator transition.