Crystals grown at Goethe University Frankfurt with rare-earth atoms display surprising, fast adjustable magnetic properties.
Computer chips and storage elements are expected to function as quickly as possible and be energy-saving at the same time. Innovative spintronic modules are at an advantage here thanks to their high speed and efficiency, as there is no lossy electrical current, rather the electrons couple with one another magnetically – like a series of tiny magnetic needles which interact with almost no friction loss. A team of scientists involving Goethe University Frankfurt and the Fritz Haber Institute in Berlin has now found promising properties with crystals grown from rare-earth atoms, which offer hope on the long path towards usage as spintronic components.
FRANKFURT. While modern computers are already very fast, they also consume vast amounts of electricity. For some years now a new technology has been much talked about, which although it is still in its infancy could one day revolutionise computer technology – spintronics. The word is a portmanteau meaning “spin” and “electronics”, because with these components electrons no longer flow through computer chips, but the spin of the electrons serves as the information carrier. A team of researchers with staff from Goethe University Frankfurt has now identified materials that have surprisingly fast properties for spintronics. The results have been published in the specialist magazine “Nature Materials”.
“You have to imagine the electron spins as if they were tiny magnetic needles which are attached to the atoms of a crystal lattice and which communicate with one another,” says Cornelius Krellner, Professor for Experimental Physics at Goethe University Frankfurt. How these magnetic needles react with one another fundamentally depends on the properties of the material. To date ferromagnetic materials have been examined in spintronics above all; with these materials – similarly to iron magnets – the magnetic needles prefer to point in one direction. In recent years, however, the focus has been placed on so-called antiferromagnets to a greater degree, because these materials are said to allow for even faster and more efficient switchability than other spintronic materials.
With antiferromagnets the neighbouring magnetic needles always point in opposite directions. If an atomic magnetic needle is pushed in one direction, the neighbouring needle turns to face in the opposite direction. This in turn causes the next but one neighbour to point in the same direction as the first needle again. “As this interplay takes place very quickly and with virtually no friction loss, it offers considerable potential for entirely new forms of electronic componentry,” explains Krellner.
Above all crystals with atoms from the group of rare earths are regarded as interesting candidates for spintronics as these comparatively heavy atoms have strong magnetic moments – chemists call the corresponding states of the electrons 4f orbitals. Among the rare-earth metals – some of which are neither rare nor expensive – are elements such as praseodymium and neodymium, which are also used in magnet technology. The research team has now studied seven materials with differing rare-earth atoms in total, from praseodymium to holmium.
The problem in the development of spintronic materials is that perfectly designed crystals are required for such components as the smallest discrepancies immediately have a negative impact on the overall magnetic order in the material. This is where the expertise in Frankfurt came into play. “The rare earths melt at about 1000 degrees Celsius, but the rhodium that is also needed for the crystal does not melt until about 2000 degrees Celsius,” says Krellner. “This is why customary crystallisation methods do not function here.”
Instead the scientists used hot indium as a solvent. The rare earths, as well as the rhodium and silicon that are required, dissolve in this at about 1500 degrees Celsius. The graphite crucible was kept at this temperature for about a week and then gently cooled. As a result the desired crystals grew in the form of thin disks with an edge length of two to three millimetres. These were then studied by the team with the aid of X-rays produced on the Berlin synchrotron BESSY II and on the Swiss Light Source of the Paul Scherrer Institute in Switzerland.
“The most important finding is that in the crystals which we have grown the rare-earth atoms react magnetically with one another very quickly and that the strength of these reactions can be specifically adjusted through the choice of atoms,” says Krellner. This opens up the path for further optimisation – ultimately spintronics is still purely fundamental research and years away from the production of commercial components.
There are still a great many problems to
be solved on the path to market maturity, however. Thus, the crystals – which
are produced in blazing heat – only deliver convincing magnetic properties at temperatures
of less than minus 170 degrees Celsius. “We suspect that the operating
temperatures can be raised significantly by adding iron atoms or similar
elements,” says Krellner. “But it remains to be seen whether the magnetic
properties are then just as positive.” Thanks to the new results the
researchers now have a better idea of where it makes sense to change parameters,
Publication: Y. W. Windsor, S.-E. Lee, D. Zahn, V. Borisov, D. Thonig, K. Kliemt, A. Ernst, C. Schüßler-Langeheine, N. Pontius, U. Staub, C. Krellner, D. V. Vyalikh, O. Eriksson, L. Rettig: Exchange scaling of ultrafast angular momentum transfer in 4f antiferromagnets. Nature Materials (2022) https://www.nature.com/articles/s41563-022-01206-4
Prof. Dr. Cornelius Krellner
Crystal and Materials Laboratory
Institute of Physics
Phone: +49 (0)69 798-47295
Important step in filming chemical reactions
An international team of scientists at the European XFEL has taken a snapshot of a cyclic molecule using a novel imaging method. Researchers from the European XFEL, DESY, Universität Hamburg and the Goethe University Frankfurt and other partners used the world's largest X-ray laser to explode the molecule iodopyridine in order to construct an image of the intact molecule from the resulting fragments. (Nature Physics, DOI 10.1038/s41567-022-01507-0).
SCHENEFELD/FRANKFURT. Exploding a photo subject in order to take its picture? An international research team at the European XFEL, the world's largest X-ray laser, applied this “extreme" method to take pictures of complex molecules. The scientists used the ultra-bright X-ray flashes generated by the facility to take snapshots of gas-phase iodopyridine molecules at atomic resolution. The X-ray laser caused the molecules to explode, and the image was reconstructed from the pieces. “Thanks to the European XFEL's extremely intense and particularly short X-ray pulses, we were able to produce an image of unprecedented clarity for this method and the size of the molecule," reports Rebecca Boll from the European XFEL, principal investigator of the experiment and one of the two first authors of the publication in the scientific journal Nature Physics in which the team describes their results. Such clear images of complex molecules have not been possible using this experimental technique until now.
The images are an important step towards recording molecular movies, which researchers hope to use in the future to observe details of biochemical and chemical reactions or physical changes at high resolution. Such films are expected to stimulate developments in various fields of research. “The method we use is particularly promising for investigating photochemical processes," explains Till Jahnke from the European XFEL and the Goethe University Frankfurt, who is a member of the core team conducting the study. Such processes in which chemical reactions are triggered by light are of great importance both in the laboratory and in nature, for example in photosynthesis and in visual processes in the eye. “The development of molecular movies is fundamental research," Jahnke explains, hoping that “the knowledge gained from them could help us to better understand such processes in the future and develop new ideas for medicine, sustainable energy production and materials research."
In the method known as Coulomb explosion imaging, a high-intensity and ultra-short X-ray laser pulse knocks a large number of electrons out of the molecule. Due to the strong electrostatic repulsion between the remaining, positively charged atoms, the molecule explodes within a few femtoseconds – a millionth of a billionth of a second. The individual ionised fragments then fly apart and are registered by a detector.
"Up to now, Coulomb explosion imaging was limited to small molecules consisting of no more than five atoms," explains Julia Schäfer from the Center for Free-Electron Laser Science (CFEL) at DESY, the other first author of the study. "With our work, we have broken this limit for this method." Iodopyridine (C5H4IN) consists of eleven atoms.
The film studio for the explosive molecule images is the SQS (Small Quantum Systems) instrument at the European XFEL. A COLTRIMS reaction microscope (REMI) developed especially for these types of investigations applies electric fields to direct the charged fragments onto a detector. The location and time of impact of the fragments are determined and then used to reconstruct their momentum – the product of mass and velocity – with which the ions hit the detector. “This information can be used to obtain details about the molecule, and with the help of models, we can reconstruct the course of reactions and processes involved," says DESY researcher Robin Santra, who led the theoretical part of the work.
Coulomb explosion imaging is particularly suitable for tracking very light atoms such as hydrogen in chemical reactions. The technique enables detailed investigations of individual molecules in the gas phase, and is therefore a complementary method for producing molecular movies, alongside those being developed for liquids and solids at other European XFEL instruments.
“We want to understand fundamental photochemical processes in detail. In the gas phase, there is no interference from other molecules or the environment. We can therefore use our technique to study individual, isolated molecules," says Jahnke. Boll adds: “We are working on investigating molecular dynamics as the next step, so that individual images can be combined into a real molecular movie, and have already conducted the first of these experiments."
The investigations involved researchers
from Universität Hamburg, the Goethe University Frankfurt, the University of
Kassel, Jiao Tong University in Shanghai, Kansas State University, the Max
Planck Institutes for Medical Research and for Nuclear Physics, the Fritz Haber
Institute of the Max Planck Society, the US accelerator laboratory SLAC, the
Hamburg cluster of excellence CUI: Advanced Imaging of Matter, the Center for
Free-Electron Laser Science at DESY, DESY and the European XFEL.
Publication: Rebecca Boll, Julia M. Schäfer, et al. X-ray multiphoton-induced Coulomb explosion images complex single molecules. Nature Physics, 2022, https://www.nature.com/articles/s41567-022-01507-0
Model of the molecule Iodopyridine (molecule_A.jpg):
The ring is formed by carbon atoms (grey) and a nitrogen atom (blue). The iodine atom (violet) is on the outside of the ring. Credit: European XFEL / Rebecca Boll, Till Jahnke
Explosion Imaging of hydrogen atoms
In this Coulomb Explosion Imaging result, the scientists have concentrated on the hydrogen atoms (violet). Here the shape of the ring can be seen better because the hydrogen atoms are the first to be emitted from the molecule due to a charge-up of the ring-atoms. The heavier nitrogen atom is emitted later in the process, when more charge has been accumulated. Accordingly, due to larger repulsion its momentum is larger than that of the hydrogen atoms. Credit: European XFEL / Rebecca Boll, Till Jahnke
Coulomb Explosion Image of carbon and
nitrogen atoms (Carbons_C.jpg):
The Coulomb Explosion Image of the molecule shows in detail the carbon atoms (red) and the nitrogen atom (green). The ring appears distorted because the detector does not register a direct image but the momentum of the fragments from the explosion, i.e., the product of their mass and velocity. The iodine atom is not displayed as it defines the horizonal axis of the momentum space coordinate system. Credit: European XFEL / Rebecca Boll, Till Jahnke
Professor Till Jahnke
European XFEL and
Institute for Nuclear Physics, Goethe-University Frankfurt
Phone: + 49 (0)69-798 47023 (Secretary)
Rebecca Boll, Ph.D.
Phone: +49 (0)40 8998 6244
Phone: +49 (0)40 8994 1905
Green chemistry needs more green toxicology
With the early assessment of sustainable, newly developed chemicals and products it is possible to assess a potential risk of toxic substances being released at a later point in product cascades. This has been revealed in a proof-of-concept study jointly coordinated by Goethe University Frankfurt and RWTH Aachen University. In the course of the study the toxicity of sustainable biosurfactants, potentially applied in, e.g., bio-shampoos, and of a new technology for the economical deployment of plant protection agents were analysed using a combination of computer modelling and laboratory experiments. The study is the first step towards a safe bioeconomy from an eco-toxicological stance, and which uses sustainable resources and processes to reduce environmental burdens significantly.
FRANKFURT. The natural resources of the planet are running short, yet at the same time they are the basis for our prosperity and development. A dilemma which the EU intends to overcome with the aid of its revised bioeconomy strategy. Rather than relying on fossil-based materials, the economy is to be based on renewable materials. These include plants, wood, microorganisms and algae. At some point in time everything is to be found in closed loops, yet the implementation of a circular bioeconomy requires a shift in the manufacture of chemicals. These also have to be produced from bio-materials rather than crude oil. Based on these requirements the American chemists Paul Anastas and John C. Warner formulated their twelve principles of green chemistry in 1998. One of their principles has very much been neglected to date, however: the reduction of the environmental toxicity of newly developed substances.
It is precisely here that the interdisciplinary project “GreenToxiConomy", which is part of the scientific alliance Bioeconomy Science Center (BioSC), comes into play. The objective was to examine bio-based substances and innovative technologies with a view to their toxic impact on the environment at an early stage in product development and to incorporate the resulting findings into product design. Project partners from Aachen, Jülich and Düsseldorf provided two of their bio-based product candidates for the analyses: microgel containers for crop protection agents and biosurfactants.
The wash-active biosurfactants for use in shampoos and detergents at BioSC are based on the synthesis abilities of the Pseudomonas putida bacterium and the Ustilago maydis fungus, respectively, rather than on crude oil. The microgel technology allows for the controlled delivery of crop protection agents because the containers ensure that the active ingredients still adhere to the plants in the event of rain.
Dr. Sarah Johann, the lead author for the study and the head of a working group in the department of evolutionary ecology and environmental toxicology at the Institute for Ecology, Evolution and Diversity at Goethe University Frankfurt, explains: “For the analysis of novel substances and technologies we have selected a broad range of concentration to be able to adequately estimate potential hazards for humans and the environment. We wanted to examine whether the bio-based surfactants were more environmentally friendly than conventional chemical surfactants. In addition, we investigated whether the microgel containers per se induce any toxicity."
To ensure the ecotoxicological evaluation was as precise as possible, the project team combined two elements in the determination of the toxicity: computer-aided prognoses (in silico) and experiments in the laboratory (in vitro and in vivo). The computer models work with the toxicity data of known chemicals, whose structure they compared with the structure of the new bio-based substances to forecast the toxicity. The experiments were conducted on aquatic and terrestrial organisms that represent specific organism groups, among them earthworms, springtails, water fleas and zebrafish embryos at a very early stage.
The result: both biosurfactants and microgels are highly promising candidates for use in a future bioeconomy whose products must be sustainably manufactured while not causing any environmental damage or harm to humans both during and after their utilisation. “We can only make statements within certain limits, however, as the transfer of laboratory results to the reality in the open field or in other applications is complicated," says Johann. More research is necessary for a holistic assessment of the risk potential, which is why follow-up projects are planned.
Prof. Henner Hollert, head of the evolutionary
ecology and environmental toxicology department at Goethe University Frankfurt,
underlines the significance of the close interdisciplinary collaboration on
“GreenToxiConomy". In the project biotechnologists and engineers jointly
designed a new product, and this was evaluated during the development stages by
eco-toxicologists from Goethe University together with a team at RWTH Aachen headed
by Prof. Dr. Martina Roß-Nickoll. “This continuous process is the major
strength of the project." Although it is only a first step towards a bioeconomy
that is safe in eco-toxicological terms, for Hollert it is already clear that
eco-toxicology and green toxicology will play a key role in the plans being
drawn up by the EU. “Whenever it is a question of future bio-based product
development and product design, we have to clarify the consequences for humans
and the environment at an early stage. In this respect our approach can provide
Publication: Sarah Johann, Fabian G. Weichert, Lukas Schröer, Lucas Stratemann, Christoph Kämpfer, Thomas-Benjamin Seiler, Sebastian Heger, Alexander Töpel, Tim Sassmann, Andrij Pich, Felix Jakob, Ulrich Schwaneberg, Peter Stoffels, Magnus Philipp, Marius Terfrüchte, Anita Loeschcke, Kerstin Schipper, Michael Feldbrügge, Nina Ihling, Jochen Büchs, Isabel Bator, Till Tiso, Lars M. Blank, Martina Roß-Nickoll, Henner Hollert. A plea for the integration of Green Toxicology in sustainable bioeconomy strategies – Biosurfactants and microgel-based pesticide release systems as examples. In: J. Hazard. Mat. 426 (2022) 127800. https://doi.org/10.1016/j.jhazmat.2021.127800
Prof. Dr. Henner Hollert
Institute of Ecology, Diversity and Evolution
Goethe University Frankfurt
Phone: +49 (0)69 798-42171
Nationwide longitudinal study in Germany investigated 250 million hospital admissions
In Germany, liver cirrhosis has the highest mortality rate of any chronic disease requiring hospital admission. When diagnosed as a comorbidity of other chronic diseases, liver cirrhosis at least doubles the mortality rate. Overall, the number of patients hospitalised with liver cirrhosis has increased throughout Germany despite the introduction of very effective drugs for treating hepatitis C, and alcohol abuse remains by far the most common cause. These are the results of a study headed by Prof. Jonel Trebicka at the University Hospital Frankfurt, which observed patients over a period of 14 years.
FRANKFURT. Cirrhosis, a disease of the liver in which tissue becomes dysfunctional and scarred, is the final stage of most chronic liver diseases and the fourth most frequent cause of death in central Europe. However, until now hardly any current findings have been available on its epidemiological profile in Germany. For this reason, Prof. Jonel Trebicka and his team of researchers investigated the data sets from the German Federal Statistical Office on the approx. 250 million hospital admissions taking place from 2005 to 2018 in Germany for any reason, and categorised them according to the Tenth Revision of the International Classification of Diseases (ICD-10). They found that 0.94 per cent of these hospitalised patients had been diagnosed with cirrhosis of the liver, which in the majority of cases occurred as a comorbidity and not the primary disease. In absolute figures, admissions of patients with liver cirrhosis rose from 151,108 to 181,688 during the observation period.
The primary end point of the study was the mortality rate from liver cirrhosis in hospital. This did indeed exhibit a welcome fall from 11.57% to 9.49% during the investigation period, but it is still much higher than the respective rates for other chronic diseases such as cardiac insufficiency (8.4%), renal failure (6.4%) and chronic obstructive pulmonary disease (5.2%). In cases where liver cirrhosis was comorbid with another chronic disease, it increased that disease's mortality rate two to three fold; the greatest effect was observed with infectious respiratory diseases.
Thanks to the introduction of direct-acting antivirals to combat Hepatitis C, the proportion of HCV-related cirrhosis fell during the observation period to around one third. On the other hand, the frequency of cirrhosis caused by non-alcoholic fatty liver disease quadrupled during the same period, in parallel with a rise in the number of obese patients. However, despite these etiological trends, cirrhosis caused by alcohol abuse continues to dominate. It accounts for 52 per cent of all cirrhoses in the study, and the absolute number is still rising.
Gastrointestinal bleeding is becoming increasingly rare as a complication of liver cirrhosis in hospital patients, presumably due to the treatment guidelines that continue to be applied in German hospitals, including endoscopic procedures or the administration of non-selective beta blockers. By 2018, bleeding from oesophageal varices had shrunk to one tenth of its original level in 2005. On the other hand, deterioration of symptoms owing to ascites or hepatic encephalopathy caused by insufficient detoxification by the liver has increased. The number of portal vein thromboses doubled in parallel with the intensified use of imaging diagnostics.
The patients admitted with cirrhosis were much younger than those with other chronic diseases: half of them were under the age of 64. Higher hospitalisation rates and in-hospital mortality rates were recorded in the eastern German states than in western Germany. Across the country, around two thirds of patients hospitalised with liver cirrhosis were men. Many of them died while in their fifties or younger, which explains the large number of disability-adjusted life years and the enormous socio-economic burden caused by liver cirrhosis, as men in this age group still account for the majority of the labour force.
“The results of our study show that the
decision-makers and financing bodies in the health system should invest much
more in the prevention of alcohol-related liver cirrhosis," Prof. Jonel
Trebicka concludes. “They also point up how important it is to recognise and treat liver cirrhosis as a comorbidity of other chronic
Publication: Wenyi Gu, Hannah Hortlik, Hans-Peter Erasmus, Louisa Schaaf, Yasmin Zeleke, Frank E. Uschner, Philip Ferstl, Martin Schulz, Kai-Henrik Peiffer, Alexander Queck, Tilman Sauerbruch, Maximilian Joseph Brol, Gernot Rohde, Cristina Sanchez, Richard Moreau, Vicente Arroyo, Stefan Zeuzem, Christoph Welsch, Jonel Trebicka: Trends and the course of liver cirrhosis and its complications in Germany: Nationwide population-based study (2005 to 2018) The Lancet Regional Health - Europe 2022;12: 100240 https://doi.org/10.1016/j.lanepe.2021.100240Further information
International research team examines photoelectric effect with the aid of a COLTRIMS reaction microscope
When light hits a material, electrons can be released from this material – the photoelectric effect. Although this effect played a major role in the development of the quantum theory, it still holds a number of secrets: To date it has not been clear how quickly the electron is released after the photon is absorbed. Jonas Rist, a Ph.D. student working within an international team of researchers at the Institute for Nuclear Physics at Goethe University Frankfurt, has now been able to find an answer to this mystery with the aid of a COLTRIMS reaction microscope which had been developed in Frankfurt: The emission takes place lightning fast, namely within just a few attoseconds – within a billionths of billionths of a second.
FRANKFURT. It is now exactly one hundred years ago that Albert Einstein was awarded the Nobel Prize in Physics for his work on the photoelectric effect. The jury had not yet really understood his revolutionary theory of relativity – but Einstein had also conducted ground-breaking work on the photoelectric effect. With his analysis he was able to demonstrate that light comprises individual packets of energy – so-called photons. This was the decisive confirmation of Max Planck's hypothesis that light is made up of quanta, and paved the way for the modern quantum theory.
Although the photoelectric effect in molecules has been studied extensively in the meantime, it has not yet been possible to determine its evolution over time in an experimental measurement. How long does it take after a light quantum has hit a molecule for an electron to be dislodged in a specific direction? “The length of time between photon absorption and electron emission is very difficult to measure because it is only a matter of attoseconds," explains Till Jahnke, the PhD-supervisor of Jonas Rist. This corresponds to just a few light oscillations. “It has so far been impossible to measure this duration directly, which is why we have now determined it indirectly." To this end the scientists used a COLTRIMS reaction microscope – a measuring device with which individual atoms and molecules can be studied in incredible detail.
The researchers fired extremely intense X-ray light – generated by the synchrotron radiation source BESSY II of Helmholtz-Zentrum Berlin – at a sample of carbon monoxide in the centre of the reaction microscope. The carbon monoxide molecule consists of one oxygen atom and one carbon atom. The X-ray beam now had exactly the right amount of energy to dislodge one of the electrons from the innermost electron shell of the carbon atom. As a result, the molecule fragments. The oxygen and carbon atoms as well as the released electron were then measured.
“And this is where quantum physics comes into play," explains Rist. “The emission of the electrons does not take place symmetrically in all directions." As carbon monoxide molecules have an outstanding axis, the emitted electrons, as long as they are still in the immediate vicinity of the molecule, are still affected by its electrostatic fields. This delays the release slightly – and to differing extents depending upon the direction in which the electrons are ejected.
As, in accordance with the laws of quantum physics, electrons not only have a particle character but also a wave character, which in the end manifests in form of an interference pattern on the detector. “On the basis of these interference effects, which we were able to measure with the reaction microscope, the duration of the delay could be determined indirectly with very high accuracy, even if the time interval is incredibly short," says Rist. “To do this, however, we had to avail of several of the possible tricks offered by quantum physics."
On the one hand the measurements showed that it does indeed only take a few dozen attoseconds to emit the electron. On the other hand, they revealed that this time interval is very heavily dependent on the direction in which the electron leaves the molecule, and that this emission time is likewise greatly dependent on the velocity of the electron.
These measurements are not only
interesting for fundamental research in the field of physics. The models which
are used to describe this type of electron dynamics are also relevant for many chemical
processes in which electrons are not released entirely, but are transferred to
neighbouring molecules, for instance, and trigger further reactions there. “In
the future such experiments could also help to better understand chemical
reaction dynamics therefore," says Jahnke.
Publication: Jonas Rist, Kim Klyssek, Nikolay M. Novikovskiy, Max Kircher, Isabel Vela-Pérez, Daniel Trabert, Sven Grundmann, Dimitrios Tsitsonis, Juliane Siebert, Angelina Geyer, Niklas Melzer, Christian Schwarz, Nils Anders, Leon Kaiser, Kilian Fehre, Alexander Hartung, Sebastian Eckart, Lothar Ph. H. Schmidt,1 Markus S. Schöffler, Vernon T. Davis, Joshua B. Williams, Florian Trinter, Reinhard Dörner,1 Philipp V. Demekhin, Till Jahnke: Measuring the photoelectron emission delay in the molecular frame. Nat Commun 12, 6657 (2021). https://doi.org/10.1038/s41467-021-26994-2
High-tech: COLTRIMS reaction microscope at electron storage ring BESSY II, Helmholtz-Zentrum Berlin für Materialien und Energie (HZB). Photo: Miriam Weller, Goethe University Frankfurt
Ph.D. student Jonas Rist, Goethe University Frankfurt. Photo: Alexander Hartung, Goethe University Frankfurt
Prof. Dr. Till Jahnke
European XFEL and
Institute for Nuclear Physics, Goethe University Frankfurt, Germany
Tel.: + 49 (0)69-798 47023 (Office)