Studies on Spin Ground States of Cubic-Symmetry Single-Molecule Magnets

最近报道了几种立方形单分子磁体(SMM)，其中大多数具有精确的立方对称性(OH)。传统SMM的磁各向异性是单轴的，与高点对称性不相容。在经典矢量图和巨旋近似的基础上研究了高度简并的自旋基态.立方形状SMM中的大自旋基态服从OH四次各向异性，对应于一组等价的经典稳定方向的8个或6个最低能级被随着S4增长的能隙很好地隔离.最低能级的精细分裂图样显示出随着2S1的增加而出现更长周期的调制，以及Kramers/Non-Kramers基态预期的奇偶效应.这些分裂应对应于各向异性势垒中半经典巨自旋的隧道分裂。

Recently several cube-shaped single-molecule magnets (SMM) were reported, most of which have exact cubic symmetry (Oh). The magnetic anisotropy in conventional SMMs is uniaxial and incompatible with higher point symmetry like Oh. The highly degenerate spin ground states are studied based on the classical vector picture and the giant-spin approximation.Giant spin ground states in cube-shaped SMMs were subjected to Oh quartic anisotropy, and eight or six lowest levels, which correspond to a set of equivalent classical stable directions, are well-isolated by an energy gap growing as ~S4.Fine-splitting patterns of lowest levels showed longer-period modulations with increasing 2S+1, in addition to odd-even effect expected for Kramers/non-Kramers ground states. These splittings should correspond to tunnel splitting of semiclassical giant spins trapped in the anisotropy wells.