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.
- Catalysis research with the X-ray microscope at BESSY IIContrary to what we learned at school, some catalysts do change during the reaction: for example, certain electrocatalysts can change their structure and composition during the reaction when an electric field is applied. The X-ray microscope TXM at BESSY II in Berlin is a unique tool for studying such changes in detail. The results help to develop innovative catalysts for a wide range of applications. One example was recently published in Nature Materials. It involved the synthesis of ammonia from waste nitrates.
- BESSY II: Magnetic ‘microflowers’ enhance magnetic fields locallyA flower-shaped structure only a few micrometres in size made of a nickel-iron alloy can concentrate and locally enhance magnetic fields. The size of the effect can be controlled by varying the geometry and number of 'petals'. This magnetic metamaterial developed by Dr Anna Palau's group at the Institut de Ciencia de Materials de Barcelona (ICMAB) in collaboration with her partners of the CHIST-ERA MetaMagIC project, has now been studied at BESSY II in collaboration with Dr Sergio Valencia. Such a device can be used to increase the sensitivity of magnetic sensors, to reduce the energy required for creating local magnetic fields, but also, at the PEEM experimental station, to study samples under much higher magnetic fields than currently possible.
- Georg Forster Research Fellow explores photocatalystsDr. Moses Alfred Oladele is working on photocatalysis for CO2 conversion in a joint project with the group of Dr. Matt Mayer, HZB, and Prof. Andreas Taubert at the University of Potsdam. The chemist from Redeemer's University in Ede, Nigeria, came to Berlin in the summer of 2024 with a Georg Forster Research Fellowship from the Alexander von Humboldt Foundation and will work at HZB for two years.