Spin Excitations and Dynamics in Molecular Nanomagnets

分子纳米磁体中的自旋激发和动力学

• 批准号: 84866817
• 负责人: Professor Dr. Oliver Waldmann
• 金额: --
• 依托单位: Arbeitsgruppe Nanophysik - Molekulare Nanomagnete
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2008
• 资助国家: 德国
• 起止时间: 2007-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/84866817?language=en
• 关键词: Spin; Excitations; Dynamics; Molecular; Nanomagnets

In molecular nanomagnets a dozen or so magnetic metal ions are linked together by organic ligands such as to form well defined structures and experience Heisenberg exchange interactions. These molecules are ideal magnetic nanoclusters as they don't exhibit form or shape dispersion and allow studying single-molecule effects by measuring bulk samples. This project aims at exploring and understanding the novel magnetic phenomena and complex many-body wave functions which can exist in these "zero-dimensional" or "mesoscopic" quantum spin systems. In the preceding project we recorded excellent inelastic neutron scattering (INS) data on the two compounds Fe9 and Mn12wheel. However, the modeling of the data turned out to be very challenging because of the complexity of both systems. We will continue our efforts and develop the magnetic model and physical understanding of the magnetism in these molecules. In the antiferromagnetic ring Fe9 the odd number of metal centers leads to a spin frustration situation, where as our previous results show the effects of Dzyaloshinski-Moriya interactions have additionally to be considered. It will be interesting to understand the interplay of spin frustration and Dzyaloshinski-Moriya interactions and the physical consequences thereof. The single-molecule magnet Mn12wheel is distinguished by unusual quantum tunneling of the magnetization which involves tunneling between states of different total spin, but the underlying physical mechanism is discussed controversially. The analysis of our previously recorded data will further the understanding of the magnetism in this cluster and resolve the discussion. We will investigate the Mn19 molecule, which has attracted huge attention as it exhibits the largest ground-state spin (S = 83/2) known for a molecular magnetic cluster. However, nothing is known about the spin excitations in this material, which we will study by INS. From preliminary work we expect that the particular topology of the (ferromagnetic) exchange interactions in this cluster leads to a low-lying excitation mode which is better described as a "collective" excitation as many transitions contribute in contrast to the "discrete" excitations common for spin clusters. Finally, we will study a newly synthesized Fe7 cluster with a novel exchange coupling topology, which may be described as a three-bladed propeller. Our preliminary analysis of the magnetic data and preliminary numerical simulations suggest a highly uncommon spin-frustration situation in this molecule. We hence will study the excitations experimentally by INS and develop the appropriate physical model. These systems allow us to study the interplay of the Heisenberg exchange interactions and the topology of the underlying lattice of spin centers from various perspectives, and will advance our incomplete understanding of the magnetism in small quantum spin clusters in general and molecular nanomagnets in particular.

在分子纳米磁体中，十几个左右的磁性金属离子通过有机配体连接在一起，从而形成明确的结构并经历海森堡交换相互作用。这些分子是理想的磁性纳米团簇，因为它们不表现出形式或形状分散性，并且允许通过测量散装样品来研究单分子效应。该项目旨在探索和理解这些“零维”或“介观”量子自旋系统中可能存在的新颖磁现象和复杂的多体波函数。在之前的项目中，我们在 Fe9 和 Mn12wheel 两种化合物上记录了出色的非弹性中子散射 (INS) 数据。然而，由于两个系统的复杂性，数据建模非常具有挑战性。我们将继续努力，开发磁性模型和对这些分子中磁性的物理理解。在反铁磁环 Fe9 中，奇数个金属中心会导致自旋挫败情况，正如我们之前的结果表明，还必须考虑 Dzyaloshinski-Moriya 相互作用的影响。了解旋转挫败和 Dzyaloshinski-Moriya 相互作用的相互作用及其物理后果将会很有趣。单分子磁体 Mn12wheel 的特点是不寻常的磁化量子隧道效应，涉及不同总自旋状态之间的隧道效应，但其基本物理机制的讨论存在争议。对我们之前记录的数据的分析将进一步了解该星团中的磁性并解决讨论。我们将研究 Mn19 分子，该分子因其表现出已知的分子磁簇中最大的基态自旋 (S = 83/2) 而引起了极大的关注。然而，我们对这种材料中的自旋激发一无所知，我们将通过 INS 对其进行研究。从初步工作中，我们预计该簇中（铁磁）交换相互作用的特定拓扑会导致低位激发模式，最好将其描述为“集体”激发，因为与自旋簇常见的“离散”激发相比，许多跃迁有所贡献。最后，我们将研究一种新合成的具有新颖交换耦合拓扑的 Fe7 团簇，它可以被描述为三叶螺旋桨。我们对磁性数据的初步分析和初步数值模拟表明该分子中存在极不常见的自旋受阻情况。因此，我们将通过 INS 实验研究激励并开发适当的物理模型。这些系统使我们能够从不同的角度研究海森堡交换相互作用和底层自旋中心晶格的拓扑结构，并将推进我们对小量子自旋簇，特别是分子纳米磁体中磁性的不完全理解。

项目成果

Multimodeling Approach to Ferromagnetic Spin-Wave Excitations in the High-Spin Cluster Mn18Sr Observed by Inelastic Neutron Scattering.

• DOI: 10.1021/acs.inorgchem.9b02134
• 发表时间: 2019-08
• 期刊: Inorganic chemistry
• 影响因子: 4.6
• 作者: Siyavash Nekuruh;J. Nehrkorn;K. Prša;J. Dreiser;A. M. Ako;C. Anson;T. Unruh;A. Powell;O. Waldmann

Ferromagnetic Cluster Spin Wave Theory: Concepts and Applications to Magnetic Molecules

铁磁团簇自旋波理论：磁性分子的概念和应用

• DOI: 10.3390/inorganics6020049
• 发表时间: 2018
• 作者: Krunoslav Prša;Oliver Waldmann
• 通讯作者: Oliver Waldmann

Inelastic Neutron Scattering Intensities of Ferromagnetic Cluster Spin Waves

铁磁团簇自旋波的非弹性中子散射强度

• DOI: 10.1002/ejic.201801170
• 发表时间: 2019
• 期刊: European Journal of Inorganic Chemistry
• 影响因子: 2.3
• 作者: Krunoslav Prša;Oliver Waldmann
• 通讯作者: Oliver Waldmann