新钴酸盐系列（BaSr）4- xLa2xCo4O15的结构和磁性
Structural and magnetic properties of the new cobaltate series (BaSr)4-xLa2xCo4O15
摘要：
报道了一类新的钴酸盐化合物（BaSr）4-xLa 2xCo 4 O 15（x = 0，0.5和1）的结构和磁性。这些化合物以六方结构结晶，其中钴离子分布在具有不同氧配位的两个不同晶体学位点之间。三个Co-O四面体和一个八面体通过共享氧原子连接形成Co 4 O 15簇，这些簇被堆积在一起形成蜂窝状网络。Sr和/或Ba原子被La部分取代允许调节Co价态混合的程度，但所有组合物仍然受到电荷随机分布的影响。磁化率与中子散射测量表明，所有研究的标本的特点是竞争铁磁和反铁磁交换相互作用，产生一个三维海森堡自旋玻璃态。中子能谱显示出一个明显的趋势，自旋动力学减慢后，增加La浓度，表明在掺杂样品中的电荷随机性减少。
英文摘要：
We report the structural and magnetic properties of a new class of cobaltates with the chemical formula (BaSr)4-xLa2xCo4O15 (x = 0, 0.5 and 1). These compounds crystallize in a hexagonal structure in which cobalt ions are distributed among two distinct crystallographic sites with different oxygen coordination. Three Co-O tetrahedra and one octahedron are linked by shared oxygen atoms to form Co4O15 clusters, which are packed together into a honeycomb-like network. Partial substitution of Sr and/or Ba atoms by La allows one to adjust the degree of Co valence mixing, but all compositions remain subject to a random distribution of charge. Magnetic susceptibility together with neutron scattering measurements reveal that all studied specimens are characterized by competing ferro- and antiferro-magnetic exchange interactions that give rise to a three dimensional Heisenberg spin-glass state. Neutron spectroscopy shows a clear trend of slowing down of spin-dynamics upon increasing La concentration, suggesting a reduction in charge randomness in the doped samples.
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