Swiss Light Source (SLS) – Page 2

Three research facilities reveal magnetic crossover

2022/09/122022/09/21

Spins tick-tock like a grandfather clock and then stop. Thanks to complementary experiments at the Swiss Muon Source SµS, Swiss Spallation Neutron Source SINQ and the Swiss Light Source SLS, researchers led by the University of Geneva have discovered this coveted characteristic, known as magnetic crossover, hidden within the magnetic landscape of an exotic layered material. Magnetic crossover means tuneability and with it promise for spin-based electronics.

A two-dimensional layered material that is magnetic and a small band gap semiconductor? For the electronics of tomorrow, you could say that Chromium Sulfide Bromide (CrSBr) has it all. “Any new magnetic features that you can find in the material can be useful from a practical point of view”, says Zurab Guguchia, scientist in muon spin spectroscopy at PSI. Together with clues from two other of PSI’s large research facilities, this technique would reveal the highly sought-after trait of magnetic crossover in this exciting new material.

The researchers discovered that as CrSBr is cooled, magnetic fluctuations in the material – where the spins tick-tock back and forth like a grandfather clock – slow down and then freeze. This process is known as magnetic crossover. Interestingly, this is a gradual ‘crossover’ from one state to another, rather than a sharp transition that occurs at one temperature. And it is this characteristic that makes it such an appealing characteristic for spin based electronics devices, as Guguchia explains:

“We believe that this dynamic magnetic behaviour comes from competing interactions and frustrations that exist between the layers in the material. This means, with an external parameter we could tune it: push it in either direction. You couldn’t do this if it was just in one boring state.”

Image: To discover the hidden order within CrSBr’s magnetic structure, researchers needed complementary evidence from three different facilities: the Swiss Muon Source, the Swiss Spallation Neutron Source and the Swiss Light Source. With these techniques, they could reveal that spin fluctuations dwindled and then froze at 40 degrees Kelvin

Credit: Paul Scherrer Institute / Mahir Dzambegovic

A piece of PSI history sets off on a long journey

2022/09/082022/09/27

Safely packed in a sturdy wooden crate, a high-tech component from PSI has begun its journey to Australia. The device was in use at PSI for more than ten years – now, with the commissioning of the Swiss X-ray free-electron laser SwissFEL, it has reached the end of its service life and will be given a new task at the Australian Synchrotron in Melbourne.

The device is carefully lifted by the indoor crane. The weight displayed on the crane’s external screen shoots up and down, eventually settling down at about 11.5 tonnes. The weight of this so-called insertion device is mainly due to its heavy steel frame. The magnets installed inside this generate attractive forces of several tonnes. The device must be able to withstand this enormous field strength. In particle accelerators, the periodic arrangement of the magnets is used to deflect electrons, thereby generating synchrotron radiation – a special type of X-rays.

Pioneering work at PSI

At PSI, the insertion device was used for a very special purpose, however. Following a lecture by an American colleague on the generation of ultra-short X-ray pulses, the two PSI physicists Gerhard Ingold and Thomas Schmidt realised that the conditions at the Swiss Light Source SLS were ideal for such a technique. The technology is called femtoslicing, and it can be used to observe extremely fast processes, such as chemical reactions.

“Immediately after the lecture was over, we did our first calculations. A few days later, the calculations turned into a project and three years later, under the leadership of Gerhard Ingold, we were finally able to produce hard X-rays in the femtosecond range for the first time in the world – a pulse of high-energy X-rays lasting 0.000 000 000 000 1 second,” as the head of the Insertion Device Group at PSI, Thomas Schmidt, recalls. Their approach was based on using the powerful magnetic field produced by this device as a modulator, so as to achieve resonance between the electrons and an external infrared laser, thereby transferring the pulse length of the latter to the X-rays. Since only a small fraction of the electrons are used in this process, namely those that overlap with the laser pulse, the technique is referred to as “slicing”.

The project resulted in numerous publications. Experiments were carried out on a range of different samples and new types of detectors were developed in order to process the extremely fast units of information. These findings were ultimately crucial to the development of free electron lasers, which are driven by linear accelerators and thus indirectly also the Swiss X-ray free-electron laser SwissFEL, where the first pilot experiments were carried out in 2017. However, this also heralded the end of the Femtoslicing Facility and thus of the insertion device in question. “SwissFEL allows us to generate much brighter and even shorter pulses of this kind of radiation than with the original facility. With this, extremely fast processes can be imaged at even higher resolutions,” says Thomas Schmidt.

Since then, the insertion device has been sitting in the hall of the SLS, unused.

Important manufacturer based in Siberia

Insertion devices are high-precision instruments, and demand for them is limited. Because of this, only a few manufacturers in the world are prepared to take on the complex task of building these devices in the first place. The world’s most important supplier of superconducting wigglers (a special type of insertion device) is based in Russia. However, due to the war and the global sanctions against Russia, many countries have also stopped importing these rare devices.

“Suddenly, there was a demand for retired wigglers in our European network for synchrotron radiation sources (LEAPS – League of European Accelerator-based Photon Sources),” explains Thomas Schmidt. “First, SOLARIS, the National Synchrotron Radiation Centre in Poland, inquired about a device that was no longer needed – we immediately agreed and sent them the plans. Unfortunately, our device was not compatible with their facility.” But just a short while later, the Australian Nuclear Science and Technology Organisation got in touch, also asking for a wiggler for their synchrotron in Melbourne. Again plans were sent – and this time everything fitted.

Image: Thomas Schmidt in the hall of the Swiss Light Source SLS. The insertion device weighing several tonnes can be seen suspended in the background, ready for transport. After being used for research at PSI more than ten years, this high-tech device will be given a new home at the Australian Synchrotron in Melbourne.

Credit: Paul Scherrer Institute/Mahir Dzambegovic

Weird fossil is not our ancestor

2022/08/172022/08/25

It has recently been supposed that humans could trace their ancestry back to a strange microscopic creature with a mouth and no anus. Thanks to analysis of 500 million year old fossils at the Swiss Light Source SLS, we can be relieved to find out this is not true: Saccorhytus is not a deuterostome like us, but an ecdysozoan. The findings, published today in Nature, make important amendments to the early phylogenetic tree and our understanding of how life developed.

In 535 million year old rocks in China is a mysterious microfossil whose evolutionary affinity is hotly debated. Saccorhytus was originally described in 2017 as an ancestral deuterostome, a member of the group from which our own deep ancestors emerged. It is microscopic in size – about a millimetre in diameter – and resembles a spikey, wrinkly sack, with a mouth surrounded by spines and holes that were interpreted as pores for gills – a primitive feature of the group. This made for a very unexpected origin of deuterostomes: within sand-grain sized organisms that may have lived among the sand or floating in the sea. However, the evidence supporting this view was always very weak – were those holes around the mouth really gill pores?

The researchers tried to address this question by collecting new specimens of Saccorhytus, dissolving tonnes of rock with strong vinegar and picking through the resulting grains of sand for these rare fossils. The fossils are no longer rare – the teams recovered hundreds of specimens, many much better preserved than any seen before, providing new insights into the anatomy and evolutionary affinity of Saccorhytus.

“Some of the fossils are so perfectly preserved that they look almost alive,” says Yunhuan Liu, professor in Palaeobiology at Chang’an University, Xi’an, China. “Saccorhytus was a curious beast, with a mouth but no anus, and rings of complex spines around its mouth.”

Image: The reconstructions show the fossil of Saccorhytus from the front

Credit: Graphic: Dinghua Yang

Reaction insights help make sustainable liquid fuels

2022/06/272022/07/07

Methanol, produced from carbon dioxide in the air, can be used to make carbon neutral fuels. But to do this, the mechanism by which methanol is turned into liquid hydrocarbons must be better understood so that the catalytic process can be optimised. Now, using sophisticated analytical techniques, researchers from ETH Zürich and Paul Scherrer Institute have gained unprecedented insight into this complex mechanism.

As we struggle to juggle the impact of emissions with our desire to maintain our energy hungry lifestyle, using carbon dioxide in the atmosphere to create new fuels is an exciting, carbon neutral alternative. One way to do this is to create methanol from carbon dioxide in the air, using a process called hydrogenation. This methanol can then be converted into hydrocarbons. Although these are then burnt, releasing carbon dioxide, this is balanced by carbon dioxide captured to make the fuel.

To fully develop this sustainable fuel, a deeper understanding of the mechanism by which methanol – in a reaction catalysed by zeolites, solid materials with unique porous architectures – is turned into long chain hydrocarbons, is necessary. With this in mind, in the frame of NCCR Catalysis, a Swiss National Center of Competence in Research, researchers from ETH Zürich joined forces with researchers from the Paul Scherrer Institut PSI to reveal the details of this reaction mechanism, the findings of which are published in the journal Nature Catalysis.

“Information is key to developing more selective and stable catalysts,” explains Javier Pérez-Ramírez, Professor of Catalysis Engineering at ETH Zürich and director of NCCR Catalysis, who co-led the study. “Prior to our study, despite many efforts, key mechanistic aspects of the complex transformation of methanol into hydrocarbons were not well understood”.

The researchers were interested in comparing the methanol to hydrocarbon process with another process: that of turning methyl chloride into hydrocarbons. Oil refineries frequently burn large quantities of unwanted methane rich natural gas. This polluting and wasteful activity results in the typical flares associated with oil refineries. “Turning methyl chloride into hydrocarbons is a kind of bridge technology,” explains Pérez-Ramírez. “Of course, we would like to move away from fossil fuels but in the meantime this would be a way to avoid wasting the vast reserves of valuable methane”.

Image: Researchers (L to R) Javier Pérez-Ramírez, András Bödi and Patrck Hemberger at the Swiss Light Source SLS

Credit: Paul Scherrer Institute / Markus Fischer

#SynchroLightAt75 – X-ray detector technology

2022/06/202022/06/20

X-Ray detectors first developed at Paul Scherrer Institute PSI in the 1990s to aid the search for the Higgs Boson at CERN and then applied to the Swiss Light Source SLS led to the spin-off, Dectris. Today this company employs over 100 people and its cutting-edge detectors are used at synchrotron and free electron laser (FEL) light sources worldwide for diverse applications ranging from protein structure determination to investigations into novel materials.

As the light source community marks #SynchroScienceAt75, we look back on this fascinating chapter in the history of light sources….

From the Higgs boson to new drugs (story published by PSI in 2016)

New ultrafast detector at the Paul Scherrer Institute

A picture-perfect example of how basic research makes solid contributions to the economy is the company DECTRIS in Baden-Dättwil, Switzerland — a spin-off of the Paul Scherrer Institute PSI, founded in 2006 and already highly successful. The detector that became, around ten years ago, the company’s founding product originated in the course of the search for the Higgs boson. Now the newest development from DECTRIS is on the market: an especially precise detector called EIGER, which is used for X-ray measurements at large research facilities. Since the fall of 2015, the newest model of the EIGER series has proven itself at the Swiss Light Source SLS. These days, researchers are writing the first scientific publications about experiments that have been carried out with the new detector. EIGER helps researchers to measure protein molecules better and more precisely than before. That in turn is of great interest for the development of new pharmaceuticals. It’s possible that urgently needed alternatives to antibiotics might be found in this way.

Image: PSI scientist Justyna Wojdyla and DECTRIS engineer Michel Stäuber with the EIGER X 16M – the spin-off company’s newest and, so far, highest-performance X-ray detector (caption from 2016)

Credit: Scanderbeg Sauer Photography

New discoveries into how the body stores zinc

2022/05/252022/06/01

Zinc deficiency is a global health problem affecting many people and results in a weak immune system in adults and especially in children. This is a challenge for health systems and is quite evident in the Mexican population, for example. Seeking explanations, researchers in Mexico teamed up with international synchrotron experts and gained new insights from studying Drosophila fruit flies, which are known to be a decent model system for human zinc metabolism.

Thanks to beamtime at BESSY II and at the SLS (PSI), they were able to show that the zinc stores in Drosophila flies depend on the tryptophan content of their diet.

“The first experiments were done on the KMC-3 spectroscopy beamline,” relates DFG Fellow Nils Schuth, who is currently researching in Mexico at the Center for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav). “We took organs from a fruit fly and performed direct measurements of the tissue. We gained very revealing information from the data. That was the first step, which already brought us forward. In a second step, we then compared the biological results with various synthesised chemical complexes.”

The project started in 2019. Then came the pandemic and travel restrictions. The next measurements were therefore performed at the Paul Scherrer Institute (PSI) on the SLS, where the two research institutes were already cooperating. In the spring of 2021, new measurements performed at BESSY II confirmed their discoveries.

Image: Confocal images of the kidney-like Malpighian tubule from a Drosophila larva at two magnifications. More details in the main article.

Credit: © Erika Garay (Cinvestav)

Spin keeps electrons in line in iron-based superconductor

2022/05/192022/05/27

Researchers from PSI’s Spectroscopy of Quantum Materials group together with scientists from Beijing Normal University have solved a puzzle at the forefront of research into iron-based superconductors: the origin of FeSe’s electronic nematicity. Using Resonant inelastic X-ray scattering (RIXS) at the Swiss Light Source (SLS), they discovered that, surprisingly, this electronic phenomenon is primarily spin driven. Electronic nematicity is believed to be an important ingredient in high-temperature superconductivity, but whether it helps or hinders it is still unknown. Their findings are published in Nature Physics.

Near PSI, where the Swiss forest is ever present in people’s lives, you often see log piles: incredibly neat log piles. Wedge shaped logs for firewood are stacked carefully lengthways but with little thought to their rotation. When particles in a material spontaneously line up, like the logs in these log piles, such that they break rotational symmetry but preserve translational symmetry, a material is said to be in a nematic state. In a liquid crystal, this means that the rod shaped molecules are able to flow like a liquid in the direction of their alignment, but not in other directions. Electronic nematicity occurs when the electron orbitals in a material align in this way. Typically, this electronic nematicity manifests itself as anisotropic electronic properties: for example, resistivity or conductivity exhibiting vastly different magnitudes when measured along different axes.

Since their discovery in 2008, the past decade has seen enormous interest in the family of iron based superconductors. Alongside the well-studied cuprate superconductors, these materials exhibit the mysterious phenomenon of high temperature superconductivity. The electronic nematic state is a ubiquitous feature of iron-based superconductors. Yet, until now, the physical origin of this electronic nematicity is a puzzle; in fact, arguably one of the most important puzzles in the study of iron-based superconductors.

Image: Resonant inelastic x-ray scattering reveals high-energy nematic spin correlations in the nematic state of the iron-based superconductor, FeSe

Credit: Beijing Normal University/Qi Tang and Xingye Lu

Rich electronic features of a kagome superconductor

2022/04/262022/05/04

The recently discovered layered kagome metals AV3Sb5 (A=K, Rb, Cs) exhibit diverse correlated phenomena, thought to be linked to so-called Van Hove singularities (VHSs) and flat bands in the material. Using a combination of polarization-dependent angle-resolved photoemission spectroscopy (ARPES) and density-functional theory, researchers led by Professor Ming Shi at the Paul Scherrer Institute directly revealed the sublattice properties of 3d-orbital VHSs and flat bands, as well as topologically non-trivial surface states in CsV3Sb5. The research reveals important insights into the material’s electronic structure and provides a basis for understanding correlation phenomena in the metals.

So-called kagome metals, named after the Japanese woven bamboo pattern their structure resembles, feature symmetrical patterns of interlaced, corner-sharing triangles. This unusual lattice geometry and its inherent features lead, in turn, to curious quantum phenomena such as unconventional, or high-temperature, superconductivity.

The potential for devices that might transport electricity without dissipation at room temperature—as well as a thirst for fundamental theoretical understanding—have led researchers to investigate this new class of quantum materials and try to figure out how electrons interact with the kagome lattice to generate such remarkable features.

A recently discovered class of AV₃Sb₅ kagome metals, where A can be =K, Rb or Cs, was shown, for instance, to feature bulk superconductivity in single crystals at a maximum Tc of 2.5 K at ambient pressure. Researchers suspect that this is a case of unconventional superconductivity, driven by some mechanism other than the phonon exchange that characterizes bonding in the electron-phonon coupled superconducting electron-pairs of conventional superconductivity.

This, as well as other exotic properties observed in the metal, are thought to be connected to its multiple “Van Hove singularities” (VHSs) near the Fermi level. VHSs, associated with the density of states (DOS), or set of different states that electrons may occupy at a particular energy level, can enhance correlation effects when a material is close to or reaches this energy level. If the Fermi level lies in the vicinity of a Van Hove point, the singular DOS determines the physical behavior due to the large number of available low-energy states. In particular, interaction effects get amplified not only in the particle-particle, but also in the particle-hole channels, leading to the notion of competing orders.

Image: Yong Hu, first author, and Nicholas Clark Plumb, who made the experimental station, at the Surface/Interface Spectroscopy (SIS) beamline of the Swiss Light Source (SLS) (L to R)

Credit: Paul Scherrer Institut / Mahir Dzambegovic

Mobile excitons as neutral information carriers

2022/02/232022/03/25

Excited about excitons? You should be. As charge neutral and thus efficient data transmitters, these quasiparticles could revolutionise electronics – but only if they can move. Now, for the first time, an international collaboration led by PSI have created and detected dispersing excitons in a metal using angle-resolved photoemission spectroscopy. They publish their observations in the journal Nature Materials.

Excitons are temporary bound states between electrons and positively charged holes, created when an electron absorbs a photon and moves to an excited state, leaving behind a hole in the valence band. Mobile excitons, due to their charge neutrality, offer great promise as a means for transmitting information without losses resulting from interactions with other charges en route. In contrast, the numerous interactions of electrons lead to resistance, heating and limitations in computational efficiency. Yet, the phenomenon of mobile excitons in metals has until now remained elusive, with traditional optical experiments only creating and detecting excitons with negligible momentum. Now, researchers at the Swiss Light Source have observed dispersing excitons with large momentum for the first time in the transition metal trichalcogenide, TaSe₃.

Image: Using ARPES, researchers could create and observe excitons diffusing along the chains of the quasi-1D metal, TaSe3. These mobile excitons come with various internal structures: interchain (red light), intrachain (pink light), or trions, formed from two electrons and a hole (blue light)

Credit: Junzhang Ma

How to get chloride ions into the cell

2022/02/032022/03/25

For the first time, a molecular movie has captured in detail the process of an anion transported across the cell membrane by a light-fueled protein pump. Publishing in Science, the researchers utilized the unique synergy of a Free Electron Laser (SwissFEL) and synchrotron light source (SLS) offered by PSI to unravel the mystery of how light energy initiates the pumping process − and how nature made sure there is no anion leakage back outside.

Many bacteria and unicellular algae have light-driven pumps in their cell membranes: proteins that change shape when exposed to photons such that they can transport charged atoms in or out of the cell. Thanks to these pumps, their unicellular owners can adjust to the environment’s pH value or salinity.

One such bacteria is Nonlabens marinus, first discovered in 2012 in the Pacific Ocean. Among others, it possesses a rhodopsin protein in its cell membrane which transports chloride anions from outside the cell to its inside. Just like in the human eye, a retinal molecule bound to the protein isomerizes when exposed to light. This isomerization starts the pumping process. Researchers now gained detailed insight into how the chloride pump in Nonlabens marinus works.

The study was led by Przemyslaw Nogly, once a postdoc at PSI and now an Ambizione Fellow and Group Leader at ETH Zürich, in close collaboration with the ALVRA team at SwissFEL and the MX team at the SLS. It is one of the first studies to fully combine experimental capabilities at these large-scale research facilities, bridging the gap in time resolution to record a full molecular movie of a protein at work. Slower dynamics in the millisecond-range were investigated via time-resolved serial crystallography at SLS while faster, up to picosecond, events were captured at SwissFEL – then both sets of data were put together.

Image: Photoactive chloride pumping through the cell membrane captured by time-resolved serial crystallography: Chloride ions (green spheres) are transported across the cell membrane by the NmHR chloride pump (pink).

Credit: Guillaume Gotthard, Sandra Mous

X-ray microscopy with 1000 tomograms per second

2021/09/242021/10/19

Tomoscopy is an imaging method in which three-dimensional images of the inside of materials are reconstructed in rapid succession. A new world record has now been set at the Swiss Light Source at the Paul Scherrer Institute: with 1000 tomograms per second, it is now possible to non-destructively capture very fast processes and structural changes in materials on the micrometre scale, such as the burning of a sparkler or the foaming of a metal alloy for the production of stable lightweight materials.

Most people are familiar with computed tomography from medicine: a part of the body is X-rayed from all sides and a three-dimensional image is then calculated, from which any sectional images can be created for diagnosis.

This method is also very useful for material analysis, non-destructive quality testing or in the development of new functional materials. However, to examine such materials with high spatial resolution and in the shortest possible time, the particularly intense X-ray light of a synchrotron light source is required. In the synchrotron light, even rapid changes and processes in material samples can be visualised if it is possible to capture 3-dimensional images in a very short time sequence.

A team led by Francisco García Moreno from the Helmholtz Centre Berlin is working on this, together with researchers from the Swiss Light Source SLS at the Paul Scherrer Institute (PSI). Two years ago, they managed a record 200 tomograms per second, calling the method of fast imaging “tomoscopy”. Now the team has achieved a new world record: with 1000 tomograms per second, they can now record even faster processes in materials or during the manufacturing process. This is achieved without any major compromises in the other parameters: the spatial resolution is still very good at several micrometres, the field of view is several square millimetres and continuous recording periods of up to several minutes are possible.

Image: Christian Schlepütz at the Tomcat beamline of the Swiss Light Source SLS, where a team of scientists have developed a 3D imaging method capable of recording 1,000 tomograms per second.

Credit: Paul Scherrer Institute/Mahir Dzambegovic

Nanobodies against SARS-CoV-2

2021/08/302021/09/16

Göttingen researchers have developed nanobodies – a type of antibodies – that efficiently block the coronavirus SARS-CoV-2 and its new variants. Those nanobodies, which originate from alpacas inoculated with part of the SARS-CoV-2 virus spike protein – the receptor-binding domain that the virus deploys for invading host cells – could serve as a potent drug against COVID-19. The researchers used the X10SA crystallography beamline at the Swiss Light Source to characterize the interaction between the nanobodies and the coronavirus spikes at the molecular level.

Unlike antibodies, nanobodies can be produced on an industrial scale and at a low cost and therefore meet the global demand for COVID-19 therapeutics. The new nanobodies, which can bind and neutralize the virus up to 1000 times better than previously developed antibodies, are currently in preparation for clinical trials.

Understanding the physics in new metals

2021/07/192021/07/21

Researchers from the Paul Scherrer Institute PSI and the Brookhaven National Laboratory (BNL), working in an international team, have developed a new method for complex X-ray studies that will aid in better understanding so-called correlated metals. These materials could prove useful for practical applications in areas such as superconductivity, data processing, and quantum computers. Today the researchers present their work in the journal Physical Review X.

In substances such as silicon or aluminium, the mutual repulsion of electrons hardly affects the material properties. Not so with so-called correlated materials, in which the electrons interact strongly with one another. The movement of one electron in a correlated material leads to a complex and coordinated reaction of the other electrons. It is precisely such coupled processes that make these correlated materials so promising for practical applications, and at the same time so complicated to understand.

Strongly correlated materials are candidates for novel high-temperature superconductors, which can conduct electricity without loss and which are used in medicine, for example, in magnetic resonance imaging. They also could be used to build electronic components, or even quantum computers, with which data can be more efficiently processed and stored.

Image: Brookhaven Lab Scientist Jonathan Pelliciari now works as a beamline scientist at the National Synchrotron Light Source II (NSLS-II), where he continues to use inelastic resonant x-ray scattering to study quantum materials such as correlated metals.

Credit: Jonathan Pelliciari/BNL

How catalysts age

2021/06/092021/06/11

PSI researchers have developed a new tomography method with which they can measure chemical properties inside catalyst materials in 3-D extremely precisely and faster than before. The application is equally important for science and industry. The researchers published their results today in the journal Science Advances.

The material group of vanadium phosphorus oxides (VPOs) is widely used as a catalyst in the chemical industry. VPOs have been used in the production of maleic anhydride since the 1970s. Maleic anhydride in turn is the starting material for the production of various plastics, increasingly including biodegradable ones. In industry, the catalytic materials are typically used for several years, because they play an important role in the chemical reactions but are not consumed in the process. Nevertheless, a VPO catalyst changes over time as a result of this use.

In a collaborative effort, scientists from two research divisions at the Paul Scherrer Institute PSI – the Photon Science Division and the Energy and Environment Division – together with researchers at ETH Zurich and the Swiss company Clariant AG, have now investigated in detail the ageing process of VPO catalysts. In the course of their research, they also developed a new experimental method.

Image: Zirui Gao, a researcher at PSI, has developed a new algorithm for experimental studies that significantly shortens the duration of certain imaging measurements that would otherwise take too long. The researchers used it to investigate ageing processes in a much-used catalyst material on the nanoscale.

Credit: Paul Scherrer Institute/Markus Fischer

Magnetic vortices come full circle

2021/05/272021/05/27

The first experimental observation of three-dimensional magnetic ‘vortex rings’ provides fundamental insight into intricate nanoscale structures inside bulk magnets, and offers fresh perspectives for magnetic devices.

Magnets often harbour hidden beauty. Take a simple fridge magnet: Somewhat counterintuitively, it is ‘sticky’ on one side but not the other. The secret lies in the way the magnetisation is arranged in a well-defined pattern within the material. More intricate magnetization textures are at the heart of many modern technologies, such as hard disk drives. Now, an international team of scientists at PSI, ETH Zurich, the University of Cambridge (UK), the Donetsk Institute for Physics and Engineering (Ukraine) and the Institute for Numerical Mathematics RAS in Moscow (Russia) report the discovery of unexpected magnetic structures inside a tiny pillar made of the magnetic material GdCo₂. As they write in a paper published today in the journal Nature Physics [1], the researchers observed sub-micrometre loop-shaped configurations, which they identified as magnetic vortex rings. Far beyond their aesthetic appeal, these textures might point the way to further complex three-dimensional structures arising in the bulk of magnets, and could one day form the basis for novel technological applications.

Mesmerising insights

Determining the magnetisation arrangement within a magnet is extraordinarily challenging, in particular for structures at the micro- and nanoscale, for which studies have been typically limited to looking at a shallow layer just below the surface. That changed in 2017 when researchers at PSI and ETH Zurich introduced a novel X‑ray method for the nanotomography of bulk magnets, which they demonstrated in experiments at the Swiss Light Source SLS [2]. That advance opened up a unique window into the inner life of magnets, providing a tool for determining three-dimensional magnetic configurations at the nanoscale within micrometre-sized samples.

Utilizing these capabilities, members of the original team, together with international collaborators, now ventured into new territory. The stunning loop shapes they observed appear in the same GdCo₂micropillar samples in which they had before detected complex magnetic configurations consisting of vortices — the sort of structures seen when water spirals down from a sink — and their topological counterparts, antivortices. That was a first, but the presence of these textures has not been surprising in itself. Unexpectedly, however, the scientists also found loops that consist of pairs of vortices and antivortices. That observation proved to be puzzling initially. With the implementation of novel sophisticated data-analysis techniques they eventually established that these structures are so-called vortex rings — in essence, doughnut-shaped vortices.

Image: Magnetic beauty within. Reconstructed vortex rings inside a magnetic micropillar.

Credit: Claire Donnelly

Quantifying oriented myelin in mouse and human brain

2021/05/262021/06/08

Myelin “insulates” our neurons enabling fast signal transduction in our brain; myelin levels, integrity, and neuron orientations are important determinants of brain development and disease. However, myelin imaging methods used in clinics or research are non-specific or destructive.

Using small-angle X-ray scattering tensor tomography (SAXS-TT), we exploited myelin’s ~17nm periodicity to non-invasively derive 3D myelin and neuron orientation maps in macroscopic tissue volumes (Figure). We demonstrated the method on a mouse brain (a-d), a mouse spinal cord, a human visual cortex and two human white matter specimens. We validated the readouts with 2D and 3D histology, and correlated the results with MRI contrasts.