How to link theory and experiment for single-chain magnets beyond the Ising model: magnetic properties modeled from ab initio calculations of molecular fragments
How to link theory and experiment for single-chain magnets beyond the Ising model: magnetic properties modeled from ab initio calculations of molecular fragments
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DOI：
10.1039/c9sc02735a
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发表时间：
2019-10-28
期刊：
影响因子：
8.4
通讯作者：
Plass, Winfried
中科院分区：
文献类型：
--
作者：
Boehme, Michael;Plass, Winfried
单链磁体等配位聚合物的磁性是基于磁畴的，磁畴是由相邻各向异性自旋中心之间的磁交换形成的。然而，基于多参考方法对这些系统进行充分的从头算量子力学处理所需的高水平理论所施加的计算限制，限制了将这种计算作为沿链金属中心的适当结构切割的单个核碎片的可行性。因此，这样的计算结果描述了单离子的性质，不能直接与代表磁畴的实验数据相关联。我们提出了一种基于n = 3-12的n元ising -自旋环的理论方法，该方法允许我们模拟磁畴并推导出SCM化合物的重要磁性能。通过对理论磁化率与实验数据的拟合，获得了单核碎片计算无法提供的磁交换。所提出的方法在钴（II）基scm中进行了测试，该scm具有三种类型的重复序列，其核和对称性不同。用该方法得到的磁参数与实验数据吻合较好。此外，用所提出的方法得到的三个测试用例的能谱都具有单个系统偏离理想伊辛行为的特征。提出了一种针对更大体系（n bbb12）的外推技术，该技术可以提供三种所研究的SCM化合物的磁畴统计平均长度的信息。
Magnetic properties of coordination polymers like single-chain magnets (SCMs) are based on magnetic domains, which are formed due to magnetic exchange between neighboring anisotropic spin centers. However, the computational restrictions imposed by the high level of theory needed for an adequate ab initio quantum mechanical treatment on the basis of multi-reference methods for these systems limit the feasibility of such calculations to mononuclear fragments as appropriate structural cutouts for the metal centers along the chains. Hence, results from such calculations describe single-ion properties and cannot be directly correlated with experimental data representing magnetic domains. We present a theoretical approach based on n-membered Ising-spin rings with n = 3-12, which allows us to simulate magnetic domains and to derive important magnetic properties for SCM compounds. Magnetic exchange, which is not provided by calculations of mononuclear fragments, is obtained by fitting the theoretical magnetic susceptibility against experimental data. The presented approach is tested for cobalt(II)-based SCMs with three types of repeating sequences, which differ in nuclearity and symmetry. The magnetic parameters derived using the presented approach were found to be in good agreement with the experimental data. Moreover, the energy spectra obtained for the three test cases using the presented approach are characteristic of a deviation of the individual systems from the ideal Ising behavior. An extrapolation technique towards larger systems (n > 12) is presented which can provide information on the statistical mean length of the magnetic domains in the three investigated SCM compounds.