Crystal growth and magnetism of novel low-dimensional van der Waals materials

磁性货车德瓦耳斯（vdW）化合物由于非常弱的vdW层间耦合而成为实现二维（2D）自旋网络的理想平台，并且因此在2D磁性的基础研究以及关于下一代自旋电子器件的应用中引起了极大的关注。在这些材料中预测了新的有趣的磁性，如不寻常的磁序类型，奇异的自旋液相和非常规的磁激发。化学组成和结构可变性的灵活性提供了一个手柄，以可控的方式在宽范围内调整这些化合物的磁性参数，从而通过实验实现理论预测的相位与所需的特性。在我们的项目中，我们提出了新的层状磁性vdW材料的高品质单晶生长和探索其静态和动态磁性能，使用亚太赫兹高场ESR（HF-ESR）光谱和互补的静态磁力测量方法。我们将从探索性合成新的单晶材料开始，沿着沿着几条路线，进行全面的分析表征，并研究静态磁性，以确定磁矩的大小，有序温度和有序类型。这将为材料合成的优化提供反馈，并为光谱HF-ESR研究提供输入。由于ESR光谱是非常敏感的磁各向异性，进入直接可测量的数量，如g因子张量和能隙的ESR激发，这种方法出现作为一个指导性的工具，调查合成的新的VDW化合物的磁相。我们将利用IFW Dresden的HF-ESR仪器的优势，该仪器能够在0.01至1 THz的非常宽的频率范围内，在高达16 T的磁场中，在低至300 mK的温度下，对ESR信号进行高灵敏度检测。系统研究单晶样品中ESR模式的频率、磁场和取向依赖性，将允许准确确定磁各向异性、基态自旋结构和低能自旋动力学参数，并将这些参数与化学成分和晶体结构联系起来。该项目的一个重要方面将是研究剥离样品，以调查磁性对样品厚度的依赖性。所获得的信息应该能够分类的研究材料相对于理论上提出的磁相，并应有助于验证2D VDW化合物的理论模型。

Magnetic van der Waals (vdW) compounds have emerged by virtue of a very weak vdW interlayer coupling as an ideal platform for realization of two-dimensional (2D) spin networks and as such have attracted significant attention both in fundamental research on 2D magnetism as well as regarding applications in the next generation of spin-electronic devices. New intriguing magnetic properties are predicted in these materials, such as unusual types of magnetic order, exotic spin liquid phases and unconventional magnetic excitations. The flexibility of the chemical composition and structural variability offer a handle to tune in a controllable way magnetic parameters of these compounds in a broad range and thus to experimentally realize the theoretically predicted phases with desired characteristics. In our project we propose to grow high quality single crystals of new layered magnetic vdW materials and explore their static and dynamic magnetic properties using sub-THz high-field ESR (HF-ESR) spectroscopy and complementary static magnetometry methods. We will start with the exploratory synthesis of new single-crystalline materials along several routes, perform their comprehensive analytical characterization and study static magnetic properties to determine the size of the magnetic moment, the ordering temperature, and the type of order. This should give a feedback for optimization of material synthesis and provide input for spectroscopic HF-ESR studies. Since ESR spectroscopy is very sensitive to magnetic anisotropies which enter in directly measurable quantities, such as the g-factor tensors and energy gaps for the ESR excitations, this method emerges as an instructive tool to investigate magnetic phases of the synthesized new vdW compounds. We will use the advantages of the HF-ESR instrumentation at the IFW Dresden which enables a high-sensitivity detection of ESR signals in a very broad frequency range from 0.01 to 1 THz, in fields up to 16 T, and at temperatures down to 300 mK. Systematic studies of frequency, magnetic field, and orientation dependences of the ESR modes in single-crystalline samples will allow an accurate determination of the magnetic anisotropies, the spin structures in the ground state, and parameters of the low-energy spin dynamics and to relate these parameters with the chemical composition and crystallographic structure. An important aspect of the project will be studies of exfoliated samples to investigate the dependence of magnetic properties on the sample thickness. The obtained information should enable to classify the studied materials with respect to the theoretically proposed magnetic phases and should help to verify theoretical models of 2D vdW compounds.