Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
Phys Rev Lett. 2013 Mar 1;110(9):097203. doi: 10.1103/PhysRevLett.110.097203. Epub 2013 Feb 26.
A unique type of frustrated lattice is found in two A-site ordered spinel oxides, LiGaCr(4)O(8) and LiInCr(4)O(8). Because of the large size mismatch between Li(+) and Ga(3+)/In(3+) ions at the A site, the pyrochlore lattice, made up of Cr(3+) ions carrying spin 3/2, becomes an alternating array of small and large tetrahedra, i.e., a "breathing" pyrochlore lattice. We introduce a parameter, the breathing factor B(f), which quantifies the degree of frustration in the pyrochlore lattice: B(f) is defined as J'/J, where J' and J are nearest-neighbor magnetic interactions in the large and small tetrahedra, respectively. LiGaCr(4)O(8) with B(f)0.6 shows magnetic susceptibility similar to that of conventional Cr spinel oxides such as ZnCr(2)O(4). In contrast, LiInCr(4)O(8) with a small B(f)0.1 exhibits a spin-gap behavior in its magnetic susceptibility, suggesting a proximity to an exotic singlet ground state. Magnetic long-range order occurs at 13.8 and 15.9 K for LiGaCr(4)O(8) and LiInCr(4)O(8), respectively, in both cases likely owing to the coupling to structural distortions.
在两种 A 位有序尖晶石氧化物 LiGaCr(4)O(8)和 LiInCr(4)O(8)中发现了一种独特类型的受挫晶格。由于 A 位上 Li(+)和 Ga(3+)/In(3+)离子的尺寸不匹配较大，由自旋为 3/2 的 Cr(3+)离子组成的萤石晶格变成了小四面体和大四面体的交替排列，即“呼吸”萤石晶格。我们引入了一个参数，即呼吸因子 B(f)，它量化了萤石晶格的受挫程度：B(f)定义为 J'/J，其中 J'和 J 分别是大四面体和小四面体中的最近邻磁相互作用。B(f)0.6 的 LiGaCr(4)O(8)表现出与 ZnCr(2)O(4)等传统 Cr 尖晶石氧化物相似的磁化率。相比之下，B(f)0.1 较小的 LiInCr(4)O(8)在其磁化率中表现出自旋能隙行为，表明其接近奇异单重态基态。LiGaCr(4)O(8)和 LiInCr(4)O(8)的磁长程有序分别在 13.8 和 15.9 K 发生，这两种情况可能都归因于与结构畸变的耦合。
