Multiferroizität in niedrigdimensionalen magnetischen Systemen mit unterschiedlichen Spins

这个德国-俄罗斯项目旨在研究howardevansite结构类型的低维混合自旋系统中的磁电和多铁性现象。这一丰富且实际上未被研究的金属氧化物家族特别包括Fe 7（PO 4）6、NaFe 7（PO 4）6、LiCuFe 2（VO 4）3和NaCuFe 2（VO 4）3，它们将在项目开始时进行研究，而新材料将进一步研究。我们的初步调查表明，存在显着的磁介电耦合的磁有序状态的一些这些化合物。目前，磁性低维材料，如howardevansite类型的手头与序列（链）的不同自旋是相当罕见的研究。在这些系统中自发电极化的出现与非共线长周期磁结构的形成有关。在本项目的框架内，将采用水热法和固相法合成以及各种复杂的实验研究。具体来说，除了标准的表征技术，我们将研究比热，热膨胀和磁致伸缩，磁化，脉冲场磁化，介电常数和介电极化。施加高达18 T（静态）和35 T（脉冲）的磁场将能够构建磁相图。此外，我们还将利用高频电子自旋共振谱和μ子自旋转动谱研究磁基态。这种丰富多样的方法将提供磁弹性介电耦合的所有相关信息，从而能够与我们的理论合作伙伴合作，阐明这类化合物的磁电耦合和多铁性的机制。作为副作用，将研究锂基材料的电化学性质，并进行原位SQUID磁力测定，以研究脱锂对磁性的影响。我们相信，该项目不仅将产生几个特定的例子，材料与强磁介电耦合实现了一种新的机制，在材料与不寻常的序列不同的自旋，但也将开辟一条通往一个新的家庭的多铁性和磁电。

This German-Russian project aims at investigating magnetoelectric and multiferroic phenomena in the class of low-dimensional mixed spin systems of the howardevansite structure type. This rich and practically uninvestigated family of metal oxides includes, in particular, Fe7(PO4)6, NaFe7(PO4)6, LiCuFe2(VO4)3, and NaCuFe2(VO4)3 which will be studied in beginning of the project while new materials will be addressed furtheron. Our preliminary investigations indicate the presence of significant magnetodielectric coupling in the magnetically ordered state of some of these compounds. At present, magnetically low-dimensional materials such as the howardevansite-type ones at hand with sequences (chains) of different spins are rather rarely studied. The appearance of spontaneous electric polarization in these systems is associated with the formation of non-collinear long-period magnetic structures. In the frame of this project, the synthesis by means of hydrothermal and solid-state methods as well as a variety of sophisticated experimental studies will be applied. To be specific, in addition to standard characterization techniques we will study the specific heat, thermal expansion and magnetostriction, magnetization, pulsed field magnetization, dielectric permittivity, and the dielectric polarization. Application of magnetic field up to 18 T (static) and 35 T (pulsed) will enable constructing the magnetic phase diagrams. In addition, the magnetic ground state will be studied by means of high-frequency Electron-Spin Resonance-Spectroscopy and Muon-Spin-Rotation. This rich variety of methods will provide all relevant information on the magneto-elastic-dielectric couplings, thereby enabling in collaboration with our theory partners to elucidate the mechanisms of magnetelectric coupling and multiferroicity in this class of compounds. As a side activity, the electrochemical properties of Li-based materials will be studied and in-situ SQUID magnetometry will be performed in order to investigate the effect of delithiation on the magnetic properties. We believe that the project will not only yield several particular examples of materials with strong magneto-dielectric coupling realized by a new mechanism in materials with unusual sequences of different spins but will also open an avenue towards a new family of multiferroics and magnetoelectrics.