Are the magnetic molecule Mo12O30(OH)10H2[Ni(H2O)3]4 and its isostructural relatives showing magnetostriction?

磁性分子表现出各种有趣的现象，如磁化的隧穿或变场中的磁滞。到目前为止，磁致伸缩不属于在分子水平上观察到的效应。然而，我们认为磁致伸缩是磁性分子中普遍存在的现象。我们在Ames(美国)和Okayama(日本)的实验合作者获得的实验结果，以及我们小组的初步理论工作，表明磁性分子Ni4表现出显著的交换参数J与外加磁场的关系。这种依赖通常是由磁致伸缩引起的，磁致伸缩改变了磁中心之间的键长度和角度。因此，该项目的目的是了解观察到的相关性，并调查可能依赖于场的各向异性或依赖于场的交换参数是否可以解释观察到的数据。最终目的是设计一个有效的哈密顿量。关键的问题是，这种效应是直接取决于外加磁场还是取决于分子的磁化强度，以及是否存在取向相关性。该项目将伴随着我们的实验合作伙伴直接测量磁致伸缩的尝试。

Magnetic molecules show a variety of interesting phenomena like tunneling of the magnetization or a hysteresis in a varying field. Magnetostriction does not belong to the effects observed on the molecular level so far. Nevertheless, we regard magnetostriction to be an ubiquitous phenomenon with magnetic molecules. Experimental results, obtained by our experimental collaborators in Ames (USA) and Okayama (Japan), together with preliminary theoretical work in our group, suggest that the magnetic molecule Ni4 shows a pronounced dependence of the exchange parameter J on the applied magnetic field. Such dependence usually results from magnetostriction which alters the bond length and angle between the magnetic centers. The aim of the project therefore is to understand the observed dependencies and to investigate whether a possibly field-dependent anisotropy or a field-dependent exchange parameter can explain the observed data. The final aim is to design an effective Hamiltonian. Crucial questions are whether the effect depends directly on the applied field or on the magnetization of the molecule as well as whether there is an orientational dependence. The project will be accompanied by attempts of our experimental partners to measure the magnetostriction directly.