Multimodeling Approach to Ferromagnetic Spin-Wave Excitations in the High-Spin Cluster Mn18Sr Observed by Inelastic Neutron Scattering.
Multimodeling Approach to Ferromagnetic Spin-Wave Excitations in the High-Spin Cluster Mn18Sr Observed by Inelastic Neutron Scattering.
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DOI：
10.1021/acs.inorgchem.9b02134
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发表时间：
2019-08
影响因子：
4.6
通讯作者：
Siyavash Nekuruh;J. Nehrkorn;K. Prša;J. Dreiser;A. M. Ako;C. Anson;T. Unruh;A. Powell;O. Waldmann
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文献类型：
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作者：
Siyavash Nekuruh;J. Nehrkorn;K. Prša;J. Dreiser;A. M. Ako;C. Anson;T. Unruh;A. Powell;O. Waldmann
用非弹性中子散射（INS）研究了具有分子内铁磁相互作用的混合价高自旋团簇[Mn 18SrO 8（N3）7Cl（MedhmpH）12（MeCN）6]Cl2（1）的磁性，并根据INS和磁性数据的同时拟合质量确定了交换耦合常数的可靠值.希尔伯特空间的巨大尺寸（3375000）和许多交换耦合常数（假设C3对称性为7）通常在大自旋团簇中遇到的挑战被解决如下：（a）限制希尔伯特空间铁磁团簇自旋波理论的结果与实验光谱数据进行了比较。因此，所观察到的INS转换被分配到自旋波激发在一个有界的铁磁自旋集团，而且可以直观的方式基于这个理论。(b)同时，量子蒙特卡罗（QMC）计算的温度依赖的磁化率与相同的参数设置进行了比较的实验数据。最先进的QMC算法的应用，如在开放源代码ALPS包中可用的，在铁磁簇中避免了完全的哈密顿对角化，而不会牺牲磁化率的计算精度，直到最低温度，这是成功分析的关键。合并后的拟合显示两个交换耦合模型具有同样良好的整体协议的数据。我们的首选模型的灵感来自磁结构相关性，并与他们一致。该模型涉及三种不同的交换相互作用，一种描述核心Mn III自旋之间的相互作用Ja = 14.3（1.0）K，两种连接核心和外围Mn II自旋的相互作用：Jb = 8.3（4）K和J6 = 3.6（4）K。使用开源的QMC软件和我们的系统方法来拟合多组由不同的实验技术获得的数据进行了详细描述，一般适用于理解大型铁磁耦合集群。
The magnetism of the mixed-valence high-spin cluster [Mn18SrO8(N3)7Cl(MedhmpH)12(MeCN)6]Cl2 (1) exhibiting intramolecular ferromagnetic interactions was studied using inelastic neutron scattering (INS), and reliable values for the exchange coupling constants were determined based on the quality of simultaneous fits to the INS and magnetic data. The challenge of the huge size of the Hilbert space (3 375 000) and many exchange coupling constants (7 assuming a C3 symmetry) generally encountered in large spin clusters was resolved as follows: (a) The results of the restricted Hilbert space ferromagnetic cluster spin wave theory were compared to the experimental spectroscopic data. The observed INS transitions were thus assigned to spin wave excitations in a bounded ferromagnetic spin cluster and moreover could be visualized in a straightforward way based on this theory. (b) Simultaneously, Quantum Monte Carlo (QMC) calculations of the temperature-dependent magnetic susceptibility with the same parameter set were compared to the experimental data. Application of state-of-the-art QMC algorithms, as available in the open source ALPS package, in ferromagnetic clusters avoids the full Hamiltonian diagonalization without sacrificing calculation accuracy of the magnetic susceptibility down to the lowest temperatures, which was crucial for the successful analysis. The combined fits revealed two exchange-coupling models with equally good overall agreement to the data. Our preferred model was inspired by magnetostructural correlations and is consistent with them. The model involves three different exchange interactions, one describing the interaction between the core MnIII spins Ja = 14.3(1.0) K and two interactions linking the core and the peripheral MnII spins: Jb = 8.3(4) K and J6 = 3.6(4) K. The use of open-source QMC software and our systematic approach to fitting multiple sets of data obtained by different experimental techniques are described in detail and are generally applicable for understanding large ferromagnetically coupled clusters.