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

• Applicants: Professor Dr. Bernd Büchner; Dr. Vladislav Kataev
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447482487

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.

• DFG Programme: Research Grants