Periodic Reporting for period 1 - FRUMALIQ (Frustrated systems with low-dimensional magnetism for magnetic refrigeration and hydrogen liquefaction)
Période du rapport: 2022-10-01 au 2024-03-31
Hydrogen, a carbon-free fuel producing only water upon reaction with oxygen, offers an alternative to fossil fuels and its favorable high energy density makes it attractive to store renewable energy. Current challenges for implementation are the transport over long distances and large-scale storage. Liquifying hydrogen is a solution; however, it requires cooling down to the hydrogen boiling point of –253 °C (20.3 K). For that, current technology consumes roughly one-third of the energy stored in liquid hydrogen. Magnetic refrigeration represents a promising alternative cooling method, offering higher efficiency, reliability, and less noisy construction, and importantly, it does not rely on harmful or greenhouse gases as a working medium. Magnetic refrigeration exploits the magnetocaloric effect, at which a magnetic material exposed to a variable magnetic field changes its temperature. Most attention has been devoted to intermetallic compounds containing rare-earth metals that rely on magnetic phase transitions in the desired temperature range, and therefore a strong magnetocaloric effect.
The overarching objective of the FRUMALIQ project is to search for suitable magnetocalorics among a distinct class of magnetic materials ¬– frustrated magnets, while avoiding rare-earth elements due to their high strategic importance. In frustrated magnets, the arrangement of magnetic atoms prevents their magnetic moments from ordering in a large temperature window, and results in many different possibilities for how correlated magnetic moments can be arranged with practically the same energy. Small applied magnetic fields then cause large changes in the magnetic state of these fascinating materials. Their inherent properties make frustrated magnets especially suitable for cooling at cryogenic temperatures – for example, close to hydrogen boiling point – and by using cheaper permanent magnets.
The main scientific objectives and activities tackled by this 18-month project can be summarized as follows. First, we synthesized rare-earth-free compounds, using abundant elements. Those compounds that classify as frustrated magnets with promising magnetic properties in the temperature range close to the boiling temperature of hydrogen were selected for fundamental characterization. Second, after an in-depth analysis of their properties, the magnetocaloric efficiency was evaluated by employing a plethora of different characterization methods. Finally, selected methods of computational chemistry were employed for advanced interpretation of the observed properties. The class of compounds we studied represents promising magnetocalorics for magnetic refrigeration for hydrogen liquefaction, and the project defines pathways for further research.
The overarching objective of the FRUMALIQ project is to search for suitable magnetocalorics among a distinct class of magnetic materials ¬– frustrated magnets, while avoiding rare-earth elements due to their high strategic importance. In frustrated magnets, the arrangement of magnetic atoms prevents their magnetic moments from ordering in a large temperature window, and results in many different possibilities for how correlated magnetic moments can be arranged with practically the same energy. Small applied magnetic fields then cause large changes in the magnetic state of these fascinating materials. Their inherent properties make frustrated magnets especially suitable for cooling at cryogenic temperatures – for example, close to hydrogen boiling point – and by using cheaper permanent magnets.
The main scientific objectives and activities tackled by this 18-month project can be summarized as follows. First, we synthesized rare-earth-free compounds, using abundant elements. Those compounds that classify as frustrated magnets with promising magnetic properties in the temperature range close to the boiling temperature of hydrogen were selected for fundamental characterization. Second, after an in-depth analysis of their properties, the magnetocaloric efficiency was evaluated by employing a plethora of different characterization methods. Finally, selected methods of computational chemistry were employed for advanced interpretation of the observed properties. The class of compounds we studied represents promising magnetocalorics for magnetic refrigeration for hydrogen liquefaction, and the project defines pathways for further research.
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.
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.
The project succeeded in identifying a promising class of frustrated magnets for magnetic cooling in the temperature range of interest, which is also highly attractive for fundamental research of exotic magnetic phases. Our research of the compounds with double-trillium lattice demonstrates that targeted adjustments to their composition can fine-tune both the magnetocaloric efficiency and the operational temperature range, while revealing fascinating physical phenomena such as orbital frustration.
The compounds studied in this project exhibit a maximum cooling effect just below the hydrogen boiling point; for application in hydrogen liquefaction technologies, peak cooling efficiency needs to reach this critical temperature and slightly above. For future implementation in devices and advancement of the technology, further research and optimization of the materials’ magnetocaloric parameters are crucial. The project lays a perfect ground for exploring the enhanced magnetocaloric effect in frustrated magnets and its advancement closer to application in an ERC Starting Grant, and the fellow will follow up with the preparation of the respective proposal.
The compounds studied in this project exhibit a maximum cooling effect just below the hydrogen boiling point; for application in hydrogen liquefaction technologies, peak cooling efficiency needs to reach this critical temperature and slightly above. For future implementation in devices and advancement of the technology, further research and optimization of the materials’ magnetocaloric parameters are crucial. The project lays a perfect ground for exploring the enhanced magnetocaloric effect in frustrated magnets and its advancement closer to application in an ERC Starting Grant, and the fellow will follow up with the preparation of the respective proposal.