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

最近报道了几种立方体形状的单分子磁体（SMM），其中大多数具有精确的立方对称（Oh）。传统smm的磁各向异性是单轴的，与Oh等较高的点对称不相容。基于经典矢量图和巨自旋近似，研究了高度简并的自旋基态。立方体smm中的巨型自旋基态受到Oh四次各向异性的影响，并且对应于一组等效的经典稳定方向的8或6个最低能级被生长为~S4的能隙很好地隔离。除了克雷默基态和非克雷默基态的奇偶效应外，最低能级的细分裂模式随着2S+1的增加显示出更长的周期调制。这些分裂应该对应于困在各向异性井中的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.