School of Physics and Astronomy, E. C. Stoner Laboratory, University of Leeds, Leeds, LS2 9JT, United Kingdom.
Phys Rev Lett. 2010 Apr 30;104(17):177202. doi: 10.1103/PhysRevLett.104.177202. Epub 2010 Apr 27.
We report on the unconventional magnetism in the cubic B-site ordered double perovskite Ba2YMoO6, using ac and dc magnetic susceptibility, heat capacity and muon spin rotation. No magnetic order is observed down to 2 K while the Weiss temperature is approximately -160 K. This is ascribed to the geometric frustration in the lattice of edge-sharing tetrahedra with orbitally degenerate Mo5+ s=1/2 spins. Our experimental results point to a gradual freezing of the spins into a disordered pattern of spin singlets, quenching the orbital degeneracy while leaving the global cubic symmetry unaffected, and providing a rare example of a valence bond glass.
我们报告了立方 B 位有序双钙钛矿 Ba2YMoO6 中的非传统磁性，使用交流和直流磁化率、热容量和 μ 子自旋旋转来研究。在 2 K 以下没有观察到磁场有序，而 Weiss 温度约为-160 K。这归因于具有轨道简并 Mo5+ s=1/2 自旋的边缘共享四面体晶格中的几何受挫。我们的实验结果表明，自旋逐渐冻结成无序的单自旋模式，猝灭轨道简并，同时保持全局立方对称性不受影响，提供了价键玻璃的一个罕见例子。
