From Dublin to Berlin as a Humboldt Research Fellow
Dr. Katarzyna Siewierska joins the group of Prof. Alexander Föhlisch as a postdoctoral Humboldt Research fellow. © Privat
Dr. Katarzyna Siewierska joins the group of Prof. Alexander Föhlisch as a postdoctoral Humboldt Research fellow. She has earned her PhD at Trinity College in Dublin, Ireland, and plans in the next two years to explore the electronic structure and spin dynamics of half-metallic thin films at BESSY II. Understanding these spintronic materials better may pave the way for more energy efficient data storage technologies.
Katarzyna Siewierska describes her project herself very clearly:
A dream material for spintronics would have low/zero net moment, no stray fields, high resonance frequency, low damping and be 100 % spin polarised, combining the best features of a metallic ferromagnet and an antiferromagnet. Such materials have the potential to revolutionise magnetic data storage and data transfer. They are called zero moment half-metals (ZMHM). This new material class was theoretically predicted in 1995, but it took almost 20 years before the first member, Mn2RuxGa, was demonstrated in 2014.
Up to now, the few other examples of ZMHMs are all Mangan-based Heusler alloys, revealing the critical role of Mangan for obtaining the uniquely desirable combination of properties. It is of great research interest to understand why this is so.
Synchrotron radiation-based techniques provide important insights into the electronic and magnetic properties of spintronic materials due to their sensitivity to spin and crystal structure, coupled with element specificity.
In this work we will combine the expertise of researchers at BESSY II in resonant inelastic X-ray scattering (RIXS) with the high quality ZMHM thin films I fabricated and studied at Trinity College Dublin (TCD) during my thesis. The goal is to confirm the half-metallic band structure of MRG, explore the spin-lattice relaxation and investigating magnon excitations to obtain information about their dispersion and the energy of ferrimagnetic resonance modes.
- What Zinc concentration in teeth revealsTeeth are composites of mineral and protein, with a bulk of bony dentin that is highly porous. This structure is allows teeth to be both strong and sensitive. Besides calcium and phosphate, teeth contain trace elements such as zinc. Using complementary microscopy imaging techniques, a team from Charité Berlin, TU Berlin and HZB has quantified the distribution of natural zinc along and across teeth in 3 dimensions. The team found that, as porosity in dentine increases towards the pulp, zinc concentration increases 5~10 fold. These results help to understand the influence of widely-used zinc-containing biomaterials (e.g. filling) and could inspire improvements in dental medicine.
- Fascinating archaeological find becomes a source of knowledgeThe Bavarian State Office for the Preservation of Historical Monuments (BLfD) has sent a rare artefact from the Middle Bronze Age to Berlin for examination using cutting-edge, non-destructive methods. It is a 3,400-year-old bronze sword, unearthed during archaeological excavations in Nördlingen, Swabia, in 2023. Experts have been able to determine how the hilt and blade are connected, as well as how the rare and well-preserved decorations on the pommel were made. This has provided valuable insight into the craft techniques employed in southern Germany during the Bronze Age. The BLfD used 3D computed tomography and X-ray diffraction to analyse internal stresses at the Helmholtz-Zentrum Berlin (HZB), as well as X-ray fluorescence spectroscopy at a BESSY II beamline supervised by the Bundesanstalt für Materialforschung und -prüfung (BAM).
- Element cobalt exhibits surprising propertiesThe element cobalt is considered a typical ferromagnet with no further secrets. However, an international team led by HZB researcher Dr. Jaime Sánchez-Barriga has now uncovered complex topological features in its electronic structure. Spin-resolved measurements of the band structure (spin-ARPES) at BESSY II revealed entangled energy bands that cross each other along extended paths in specific crystallographic directions, even at room temperature. As a result, cobalt can be considered as a highly tunable and unexpectedly rich topological platform, opening new perspectives for exploiting magnetic topological states in future information technologies.