巨型单分子磁体{Mn$_{70}$}和{Mn$_{84}$}的低自旋基态
Low-spin ground state of the giant single-molecule magnets {Mn$_{70}$} and {Mn$_{84}$}
AI总结：
本研究利用SU(2)对称DMRG计算含DFT交换参数的量子Heisenberg模型，解释{Mn$_{70}$}与{Mn$_{84}$}的低自旋基态及磁化平台。
摘要：
单分子磁体{Mn$_{70}$}和{Mn$_{84}$}的特征是具有一个14格点单元胞，其中$S=2$自旋格点排列成圆形几何结构。实验上，这些体系表现出总自旋显著较低的磁基态，$S_{\text{tot}}=5-7$。迄今为止，由于如此大体系的量子Heisenberg模型十分复杂，这种低自旋基态在理论上一直难以描述。在本工作中，我们填补了这一空白，并证明{Mn$_{70}$}和{Mn$_{84}$}的基态实际上由较小的有限$S_{\text{tot}}$支配，与实验定量一致。我们对一个量子Heisenberg模型采用精确的大规模SU(2)对称密度矩阵重整化群计算，该模型使用先前由密度泛函理论得到的已发表交换参数。在相同参数和$S=1$下，我们没有发现低自旋态，因此提出$S\geq2$的阻挫体系本质上倾向于弱铁磁相互作用。这可以解释类似的低自旋Mn基单分子磁体为何普遍存在。最后，我们计算了完整磁化曲线，发现位于饱和值10/14、11/14、12/14和13/14处的宽平台，这可追溯到簇间键断裂的近独立3格点簇。
英文摘要：
The single-molecule magnets {Mn$_{70}$} and {Mn$_{84}$} are characterized by a 14-site unit cell with $S=2$ spin sites arranged in a circular geometry. Experimentally, these systems exhibit a magnetic ground state with a notably low total spin $S_{\text{tot}}=5-7$. Up to now, this low-spin ground state has been up difficult to describe theoretically due to the complexity of the quantum Heisenberg model for such a large system. In this work, we fill this gap and demonstrate that the ground state of {Mn$_{70}$} and {Mn$_{84}$} is in fact governed by a small, finite $S_{\text{tot}}$ in quantitative agreement with the experiment. We employ accurate, large-scale SU(2)-symmetric density-matrix renormalization group calculations for a quantum Heisenberg model with previously published exchange parameters obtained by density-functional theory. We do not find a low-spin state for the same parameters and $S=1$ and thus propose that frustrated systems with $S\geq2$ are inherently prone to weak ferromagnetic interactions. This could account for the prevalence of similar low-spin Mn-based single-molecule magnets. Finally, we compute the full magnetization curve and find wide plateaus at 10/14, 11/14, 12/14 and 13/14 of the saturation, which can be traced back to nearly-independent 3-site clusters with broken inter-cluster bonds.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
