To synthesize novel frustrated magnets, four synthetic pathways were consecutively followed, on which the fellow gained experience with various synthetic methods of solid-state chemistry such as hydrothermal synthesis, and metallothermic reduction or flux methods carried out in crucibles or evacuated sealed silica ampoules under inert atmospheres. Selected reactions were also studied by thermal analysis to see at which temperatures the reaction takes place, to better plan the reaction conditions. The products of the syntheses were analyzed by powder X-ray diffraction, which revealed phase composition and purity. Some of the syntheses or capillaries with samples for X-ray diffraction were prepared in a glove box with an argon atmosphere. The morphology of selected samples was analyzed in a scanning electron microscope and their elemental composition by a related energy-dispersive X-ray analysis. Compounds of the langbeinite structure type containing magnetic ions were selected for more sophisticated analyses based on careful consideration. These compounds have a fascinating crystal structure, where two distinguishable sets of magnetic ions form two interlinked networks of corner-sharing equilateral triangles (so-called double-trillium lattice). In addition, their Curie-Weiss temperature, the characteristic temperature showing the strength of magnetic interactions in a material, falls near the boiling point of hydrogen.
The magnetic properties of these compounds in dependence on temperature and applied magnetic field were thoroughly analyzed by using direct-current magnetometry. Thermal properties indicate degrees of freedom in the material and were studied by variable-temperature molar-heat-capacity measurements in various applied magnetic fields. Combining the results of magnetic and heat-capacity analyses allowed the determination of magnetocaloric parameters, which characterize the efficiency of the compounds for magnetic cooling. The analysis of temperature-dependent 57Fe Mössbauer spectra, using the 57Fe nuclei as a sensitive local probe in the material, provided in-depth insights into specific surroundings, local magnetic fields, or fluctuations. Furthermore, the magnetic structure of a selected compound with interesting properties deduced from Mössbauer spectroscopy was studied by neutron diffraction at the HB-2A beamline of the High Flux Isotope Reactor, Oak Ridge National Laboratory (TN, USA, beam time awarded under proposal no. IPTS-31426.1) where a magnetic phase transition to an ordered state at –272 °C was discovered. The complexity of langbeinite-type compounds rendered analyses by quantum chemistry calculations impractical, and therefore alternative, more suitable calculation methods, such as ligand-field calculations within the framework of the angular overlap model, were employed to interpret the observed experimental data.
The scientific results were presented at three international conferences in Europe, one international workshop, and two seminar talks abroad, as well as summarized in two articles, one of which is under revision and one in final preparations at the time of report submission.
