Electronic and magnetic properties of novel iron oxides at high pressure and wide temperature conditions

• Applicant: Professorin Carmen Sanchez-Valle, Ph.D., since 10/2022
• Subject Area: Experimental Condensed Matter Physics ; Mineralogy, Petrology and Geochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449164533

It was found over the last decade that the family of the iron oxides is not limited by the three well-known stoichiometries, FeO, Fe2O3, and Fe3O4, but includes unconventional stoichiometries such as Fe2O, Fe4O5, Fe5O6, Fe7O9, Fe25O32. The discovery of those new structures became possible employing state-of-the-art high-pressure high-temperature synthesis and advanced single-crystal and powder X-ray diffraction methods. While generally, structural and - at ambient pressure - some other properties of the novel oxides are available, information about their electronic and magnetic properties at extreme pressure-temperature conditions is very limited. This project aims at addressing this issue by exploring the electronic and magnetic transitions in novel iron oxides at high pressures and over a wide range of temperatures employing a combination of state-of-the-art synchrotron X-ray techniques and theoretical calculations developed and/or applied in our groups.The main techniques, which are planned to be used, are nuclear forward scattering (NFS) of synchrotron radiation and synchrotron Mössbauer spectroscopy with the newly developed synchrotron Mössbauer source (SMS). Both techniques are based on nuclear resonance scattering on the 57Fe Mössbauer transition in the time and energy domain, respectively. Over the last two decades, these two methods have demonstrated their unique power in the exploration of the electronic and magnetic properties of iron-containing systems at extreme conditions. Among them, the SMS spectroscopy especially facilitates the study of complex systems with multiphase assemblage. Currently, however, studies are limited to samples with structures above 10 μm due to the insufficient quality of the iron borate crystals, key elements of the SMS, generating x-ray beam spot sizes of about 10 μm.We plan in this project to improve the quality of the borate crystals to allow for high-quality x-ray optics with better focusing capabilities in order to facilitate our challenging investigations. Our group has ample experience in the growth of single crystals and has achieved the first success in the growth of borate crystals.Perfect borate crystals together with the upgraded European Synchrotron Radiation Facility (ESRF) and the foreseen installation of an SMS at PETRA at the Deutsches Elektronen-Synchrotron (DESY) would put those techniques further to the forefront of experimental techniques. The new instruments would not only facilitate our studies but also extend our studies to the novel iron oxides existing only as a part of the multiphase assemblage. Once in place at the two synchrotron facilities, a new cutting-edge instrument will be available for its use also by other groups and communities.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Dr. Natalia Kazak, until 3/2022
• Ehemaliger Antragsteller: Dr. Ilya Kupenko, until 10/2022