BESSY II: Magnetic ‘microflowers’ enhance magnetic fields locally
The magnetic microstructure of the nickel-iron alloy leads to a compression of the field lines in the centre. © A. Palau/ICMAB
Two magnetic contrast maps. The cobalt rod is located in the centre of the microflower. © S. Valencia /HZB
A 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.
Dr Anna Palau from the Institut de Ciencia de Materials de Barcelona (ICMAB) has developed a special metamaterial that looks like tiny flowers under the scanning electron microscope. The 'petals' consist of strips of a ferromagnetic nickel-iron alloy. The microflowers can be produced in various geometries, not only with different inner and outer radii, but also with variable numbers and widths of petals. This flower-shaped geometry causes the field lines of an external magnetic field to concentrate in the centre of the device, resulting on a greatly intensified magnetic field.
Magnetic metamaterials
'Metamaterials are artificially produced materials with microstructures whose dimensions are smaller than the electromagnetic or thermal waves they are designed to manipulate,' explains Anna Palau. The physicist is working on magnetic microstructures that can be used in data storage, information processing, biomedicine, catalysis and magnetic sensor technology. By using these metamaterials, the sensitivity of magnetic sensors could be highly increased, as the magnetic field to be detected would be amplified at the center of these systems.
Mapping magnetic domains at BESSY II
Anna Palau, her student Aleix Barrera, and Sergio Valencia have now investigated this at the XPEEM experimental station at BESSY II. They placed a cobalt rod in the centre of various microflowers as a sensor for the magnetic field and mapped the magnetic domains inside the cobalt rod. 'By adjusting the geometric parameters such as shape, size and number of petals, the magnetic behaviour can be switched and controlled,' says Valencia. As a result, the sensitivity of a magnetoresistive sensor could be increased by more than two orders of magnitude.
New options, also for experiments at XPEEM
This innovation opens up new technological options for improving the performance of small magnetic sensors and for developing multifunctional magnetic components. In the future, such microstructures could be used to generate much higher magnetic fields locally, which is also of interest for the experimental XPEEM station at BESSY II. 'Our experimental system is a photoemission electron microscope, so magnetic fields deflect the electrons and make the experiments difficult,' says Valencia. 'The maximum magnetic field we can normally apply for imaging is about 25 millitesla (mT). With the magnetic field concentrator, where the field is only locally enhanced, we can easily achieve fields five times higher.' This is very exciting because it opens up the possibility of studying a range of magnetic systems under conditions that have not been possible before.
- The future of corals – what X-rays can tell usThis summer, it was all over the media. Driven by the climate crisis, the oceans have now also passed a critical point, the absorption of CO2 is making the oceans increasingly acidic. The shells of certain sea snails are already showing the first signs of damage. But also the skeleton structures of coral reefs are deteriorating in more acidic conditions. This is especially concerning given that corals are already suffering from marine heatwaves and pollution, which are leading to bleaching and finally to the death of entire reefs worldwide. But how exactly does ocean acidification affect reef structures?
Prof. Dr. Tali Mass, a marine biologist from the University of Haifa, Israel, is an expert on stony corals. Together with Prof. Dr. Paul Zaslansky, X-ray imaging expert from Charité Berlin, she investigated at BESSY II the skeleton formation in baby corals, raised under different pH conditions. Antonia Rötger spoke online with the two experts about the results of their recent study and the future of coral reefs.
- Susanne Nies appointed to EU advisory group on Green DealDr. Susanne Nies heads the Green Deal Ukraina project at HZB, which aims to support the development of a sustainable energy system in Ukraine. The energy expert has now also been appointed to the European Commission's scientific advisory group to comment on regulatory burdens in connection with the net-zero target (DG GROW).
- Long-term stability for perovskite solar cells: a big step forwardPerovskite solar cells are inexpensive to produce and generate a high amount of electric power per surface area. However, they are not yet stable enough, losing efficiency more rapidly than the silicon market standard. Now, an international team led by Prof. Dr. Antonio Abate has dramatically increased their stability by applying a novel coating to the interface between the surface of the perovskite and the top contact layer. This has even boosted efficiency to almost 27%, which represents the state-of-the-art. After 1,200 hours of continuous operation under standard illumination, no decrease in efficiency was observed. The study involved research teams from China, Italy, Switzerland and Germany and has been published in Nature Photonics.