magnetism – Lightsources.org

World changing science with precious photons

2022/02/102022/02/10

he 3.4 km long European XFEL generates extremely intense X-ray flashes used by researchers from all over the world. The flashes are produced in underground tunnels and they enable scientists to conduct a wide range of experiments including mapping atomic details of viruses, filming chemical reactions, and studying processes in the interior of planets.

Michael Schneider is a physicist at the Max Born Institute in Berlin. He uses synchrotrons and free electron lasers, such as the European XFEL, to study magnetism and magnetic materials. Michael’s fascinating #LightSourceSelfie takes you inside the European XFEL where he recalls the fact that it was large scale facilities themselves that first attracted him to his area of fundamental research. The work is bringing us closer to a new generation of computing devices that work more like the neurons in our brains that the transistors that we currently have in our computers. Michael captures the dedication of his colleagues and the facility teams, along with the type of work that you can get involved with at large scale facilities. He also gives a brilliant overview of the stages involved in conducting research at a light source. Michael is clearly very passionate about his science, but also finds time for some great hobbies too!

Ultrafast magnetism: heating magnets, freezing time

2021/10/152021/10/25

Magnetic solids can be demagnetized quickly with a short laser pulse, and there are already so-called HAMR (Heat Assisted Magnetic Recording) memories on the market that function according to this principle. However, the microscopic mechanisms of ultrafast demagnetization remain unclear. Now, a team at HZB has developed a new method at BESSY II to quantify one of these mechanisms and applied it to the rare-earth element Gadolinium, whose magnetic properties are caused by electrons on both the 4f and the 5d shells. This study is completing a series of experiments done by the team on Nickel, Iron-Nickel Alloys. Understanding these mechanisms is useful for developing ultrafast data storage devices.

New materials should make information processing more efficient, for example, through ultrafast spintronic devices that store data with less energy input. But to date, the microscopic mechanisms of ultrafast demagnetization are not fully understood. Typically, the process of demagnetization is studied by sending an ultrashort laser pulse to the sample, thereby heating it up, and then analyzing how the system evolves in the first picoseconds afterward.

Read more on the HZB website.

Image: The picture shows the glowing filament which keeps the sample at constant temperatures during the measurements.

Credit: © HZB

Tuning the magnetic anisotropy of lanthanides

2021/08/112021/08/24

The magnetism of lanthanide-directed nanoarchitectures on surfaces can be drastically affected by small structural changes. The study carried out in a collaboration between researchers from IMDEA Nanociencia and BOREAS beamline at ALBA reports the effect of the coordination environment in the reorientation of the magnetic easy axis of dysprosium-directed metal-organic networks on Cu(111). The authors show that the magnetic anisotropy of lanthanide elements on surfaces can be tailored by specific coordinative metal-organic protocols.

Recent findings have highlighted the potential of lanthanides in single atom magnetism. The stabilization of single atom magnets represents the ultimate limit on the reduction of storage devices. However, single standing atoms adsorbed on surfaces are not suitable for practical applications due to their high diffusion, i.e., low thermal stability. The next step towards more realistic systems is the coordination of these atoms in metal-organic networks.In 4f elements, the spin-orbit coupling (SOC) is larger than the crystal field, which might result in higher anisotropies. Furthermore, the crystal field acts as a perturbation of the SOC and can be tailored to increase the anisotropy by choosing an appropriate coordination environment. The strong localization of the 4f states reduces the hybridization with the surface, increasing the spin lifetimes, which is crucial, since a long magnetic relaxation time is mandatory for technological applications.

Read more on the ALBA website

Image: Cover picture showing the structure of the Dy-TPA network where C, H, O and Dy atoms are represented by black, red and green balls, respectively, the tilted orientation of the magnetic easy axis is represented by green arrows.

Credit: ALBA

Dynamic, yet inertial – and definitely futuristic

2020/10/072020/10/07

Researchers conduct experiments to demonstrate inertial motion in magnetic materials

In the journal Nature Physics (DOI: 10.1038/s41567-020-01040-y), an international team of scientists from Germany, Italy, Sweden, and France report on their experimental observation of an inertial effect of electron spins in magnetic materials, which had previously been predicted, but difficult to demonstrate. The results are the outcome of one of the first long-term projects at the high-power terahertz light source TELBE at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR).

Today, most of the world’s “memory” is stored on magnetic data carriers – hard disks – without which our digital lives would be unthinkable. In the magnetic material, it is the electron spins that do the actual job of storing the data. Imagine this spin as electrons rotating around their own axes, either to the left or right – representing the digital “zeros” and “ones”.

There is something special about this rotation, as Dr. Jan-Christoph Deinert from the HZDR Institute of Radiation Physics explains: “In the magnetic field, the electron behaves like a tumbling spinning top. The rotational axis of the electron changes its direction on a circular path. We call this process precession. When disturbed by an external force, the rotational axis should also make small oscillatory movements, called nutation, which overlap the precession. Like precession, it is a characteristic of many rotating objects, from children’s spinning tops to planets like Earth. Due to its much smaller scale, however, nutation is far more difficult to observe.”

Read more on the Helzholtz Zentrum Dresden Rossendorf website

Image: An international team of scientists has managed for the first time to observe the ‘nutation’ of spins in magnetic materials (the oscillations of their axis during precession). Foto: Dunia Maccagni

Accoustic spin waves: towards a new paradigm of on-chip communication

2020/04/062020/04/09

For the first time researchers have observed directly sound-driven spin waves (magnetoacoustic waves) and have revealed its nature.

Results show that these magnetization waves can go up to longer distances (up to centimeters) and have larger amplitudes than the commonly known spin waves. The study, published in Phys. Rev. Lett., is carried out by researchers from the University of Barcelona (UB), the Institute of Materials Science of Barcelona (ICMAB-CSIC), and the ALBA Synchrotron, in collaboration with the Paul-Drude-Institut in Berlin.

Researchers have observed directly and for the first time magnetoacoustic waves (sound-driven spin waves), which are considered as potential information carriers for novel computation schemes. These waves have been generated and observed on hybrid magnetic/piezoelectric devices. The experiments were designed by a collaboration between the University of Barcelona (UB), the Institute of Materials Science of Barcelona (ICMAB-CSIC) and the ALBA Synchrotron. The results show that magnetoacoustic waves can travel over long distances -up to centimeters- and have larger amplitudes than expected.

>Read more on the ALBA website

Image: TOP: A propagating and a standing magnetization wave in ferromagnetic Nickel, driven by magnetoelastic coupling to a surface acoustic wave in a piezoelectric LiNbO₃substrate. The images combine line profiles (color indicating the local magnetization direction) at different delay times between the probing X-ray pulse and the electrical SAW excitation.
BOTTOM: Scheme of the strain caused by the surface acoustic waves (SAWs) in the piezoelectric (in green color scale) and magnetic modulation in the ferromagnetic material (in orange-cyan color scale).

Dynamic pattern of skyrmions observed

2019/10/152019/10/21

Tiny magnetic vortices known as skyrmions form in certain magnetic materials, such as Cu₂OSeO₃.

These skyrmions can be controlled by low-level electrical currents – which could facilitate more energy-efficient data processing. Now a team has succeeded in developing a new technique at the VEKMAG station of BESSY II for precisely measuring these vortices and observing their three different predicted characteristic oscillation modes (Eigen modes).

Cu₂OSeO₃ is a material with unusual magnetic properties. Magnetic spin vortices known as skyrmions are formed within a certain temperature range when in the presence of a small external magnetic field. Currently, moderately low temperatures of around 60 Kelvin (-213 degrees Celsius) are required to stabilise their phase, but it appears possible to shift this temperature range to room temperature. The exciting thing about skyrmions is that they can be set in motion and controlled very easily, thus offering new opportunities to reduce the energy required for data processing.

Image: The illustration demonstrates skyrmions in one of their Eigen modes (clockwise).
Credit: Yotta Kippe/HZB

New material with magnetic shape memory

2019/06/042019/06/20

Researchers at the Paul Scherrer Institute PSI and ETH Zurich have developed a new material whose shape memory is activated by magnetism.

It retains a given shape when it is put into a magnetic field. It is a composite material consisting of two components. What is special about the new material is that, unlike previous shape-memory materials, it consists of a polymer and droplets of a so-called magnetorheological fluid embedded in it. Areas of application for this new type of composite material include medicine, aerospace, electronics and robotics. The researchers are now publishing their results in the scientific journal Advanced Materials.
It looks like a magic trick: A magnet moves away from a black, twisted band and the band relaxes –without any further effect (see video). What looks like magic can be explained by magnetism. The black ribbon consists of a composite of two components: a silicone-based polymer and small droplets of water and glycerine in which tiny particles of carbonyl iron float. The latter provide the magnetic properties of the material and its shape memory. If the composite material is forced into a certain shape with tweezers and then exposed to a magnetic field, this shape is retained even when the tweezers are removed. Only when the magnetic field is also removed does the material return to its original shape.

Image: Paolo Testa, first author of the study, with a model of the overall structure of the shape-memory material
Credit: Paul Scherrer Institute/Mahir Dzambegovic

Coherent scattering imaging of skyrmions

2019/05/102019/05/28

Profiting from the coherence of synchrotron light, scientists have performed both reciprocal and real-space observations of magnetic skyrmion lattice deformation in a chiral magnet Co8Zn8Mn4.

The study of these materials is key for developing futures spintronic applications such as racetrack memory and logic devices.
The interplay between exchange interaction, antisymmetric Dzyaloshinskii-Moriya interaction, and magnetocrystalline anisotropy may cause incommensurate spin phases such as helical, conical, and Bloch-type skyrmion lattice states. The typical size of a magnetic skyrmion varies in a range from a few to a few hundred nanometers which makes them promising candidates for future spintronic applications such as skyrmion racetrack memory – with storage density higher than solid-state memory devices- and logic devices.
Coherent soft X-ray scattering and imaging are powerful tools to study the spin ordering in multicomponent magnetic compounds with element selectivity.
In this experiment, a skyrmion-hosting compound Co₈Zn₈Mn₄ was investigated at cryogenic temperatures and applied high magnetic fields by a group of researchers from the Japanese RIKEN Center of Emergent Matter Science, National Institute for Materials Science, the Science and Technology Agency, University of Tokyo, the Institute of Materials Structure Science and Photon Factory, as well as from the ALBA Synchrotron.

>Read more on the ALBA website

Image: Coherent soft x-ray speckle patterns measured for Co₈Zn₈Mn₄ sample at L3 absorption edge of Co at different temperatures 150 K, 120 K, 25 K (top panel, left to right) and applied field of 70 mT. White scale bar corresponds to 0.05 nm−1. Bottom panel shows micromagnetic simulations of the corresponding skyrmionic spin textures.

A compass pointing West

2019/03/292019/04/11

Researchers at the Paul Scherrer Institute PSI and ETH Zurich have discovered a special phenomenon of magnetism in the nano range.

It enables magnets to be assembled in unusual configurations. This could be used to build computer memories and switches to increase the performance of microprocessors. The results of the work have now been published in the journal Science.
Magnets are characterized by the fact that they have a North pole and a South pole. If two common magnets are held close to each other, opposite poles attract and like poles repel each other. This is why magnetic needles, such as those found in a compass, align themselves in the Earth’s magnetic field so that we can use them to determine the cardinal directions North and South and, derived from this, East and West. In the world that we experience every day with our senses, this rule is correct. However, if you leave the macroscopic world and dive into depths of much smaller dimensions, this changes. Researchers at the Paul Scherrer Institute PSI and the ETH Zurich have now discovered a very special magnetic interaction at the level of nanoscopic structures made of magnetic layers only a few atoms thick.

Image: Zhaochu Luo, lead author of the study, in front of a so-called sputter deposition tool. In the apparatus the layers of platinum, cobalt and aluminium oxide are produced. Each layer is only a few nanometers thick. Credit: Paul Scherrer Institute/Mahir Dzambegovic

How to catch a magnetic monopole in the act

2019/03/042019/03/08

Berkeley Lab-led study could lead to smaller memory devices, microelectronics, and spintronics

A research team led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has created a nanoscale “playground” on a chip that simulates the formation of exotic magnetic particles called monopoles. The study – published recently in Science Advances – could unlock the secrets to ever-smaller, more powerful memory devices, microelectronics, and next-generation hard drives that employ the power of magnetic spin to store data.

Follow the ‘ice rules’
For years, other researchers have been trying to create a real-world model of a magnetic monopole – a theoretical magnetic, subatomic particle that has a single north or south pole. These elusive particles can be simulated and observed by manufacturing artificial spin ice materials – large arrays of nanomagnets that have structures analogous to water ice – wherein the arrangement of atoms isn’t perfectly symmetrical, leading to residual north or south poles.

Image: Full image here. This nanoscale “playground” on a chip uses nanomagnets to simulate the formation of exotic magnetic particles called “monopoles.” Credit: Farhan/Berkeley Lab

Superferromagnetism with electric-field induced strain

2019/02/152019/03/19

Data storage in today’s magnetic media is very energy consuming. Combination of novel materials and the coupling between their properties could reduce the energy needed to control magnetic memories thus contributing to a smaller carbon footprint of the IT sector. Now an international team led by HZB has observed at the HZB lightsource BESSY II a new phenomenon in iron nanograins: whereas normally the magnetic moments of the iron grains are disordered with respect each other at room temperature, this can be changed by applying an electric field: This field induces locally a strain on the system leading to the formation of a so-called superferromagnetic ordered state.
Switching magnetic domains in magnetic memories requires normally magnetic fields which are generated by electrical currents, hence requiring large amounts of electrical power. Now, teams from France, Spain and Germany have demonstrated the feasibility of another approach at the nanoscale: “We can induce magnetic order on a small region of our sample by employing a small electric field instead of using magnetic fields”, Dr. Sergio Valencia, HZB, points out.

Image: The cones represents the magnetization of the nanoparticles. In the absence of electric field (strain-free state) the size and separation between particles leads to a random orientation of their magnetization, known as superparamagnetism
Credit: HZB

First commissioning results for insertion devices published

2019/02/142019/02/28

The intense X-ray light for each of the MAX IV beamlines is generated when fast electrons fly through an array of magnets, placed in a so-called insertion device.

In a recent report, our insertion device team present the commissioning results for the first nine of these beamline specific instruments.
At synchrotrons like MAX IV, we accelerate electrons to velocities close to the speed of light. The electrons are injected into storage rings where they travel turn after turn inside a vacuum tube, guided by the strong forces of hundreds of carefully tuned magnets. At certain places along the electron path, the magnets are arranged in arrays called insertion devices that make the electrons wiggle from side to side as they fly through. When the electrons perform this motion, they emit energy in the form of intense X-rays. Each beamline needs its dedicated insertion device, built to produce X-rays optimised for the measurement techniques performed there.
The insertion device team have now published the first commissioning results. At the time the report was written, twelve insertion devices were installed, and nine successfully commissioned to deliver according to specifications. Six of them have been built in-house, and two are transferred from the old MAX-lab and refurbished. The remaining insertion devices come from Hitachi and our French synchrotron colleague SOLEIL.

New insight into a puzzling magnetic phenomenon

2019/01/142019/02/21

ImagUsing an X-ray laser, researchers watched atoms rotate on the surface of a material that was demagnetized in millionths of a billionth of a second.

More than 100 years ago, Albert Einstein and Wander Johannes de Haas discovered that when they used a magnetic field to flip the magnetic state of an iron bar dangling from a thread, the bar began to rotate.

Now experiments at the Department of Energy’s SLAC National Accelerator Laboratory have seen for the first time what happens when magnetic materials are demagnetized at ultrafast speeds of millionths of a billionth of a second: The atoms on the surface of the material move, much like the iron bar did. The work, done at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, was published in Nature earlier this month.

>Read more on the LCLS at SLAC website

Image: Researchers from ETH Zurich in Switzerland used LCLS to show a link between ultrafast demagnetization and an effect that Einstein helped discover 100 years ago.
Credit: Dawn Harmer/SLAC National Accelerator Laboratory

Tunable ferromagnetism in a 2D material at room temperature

2018/12/052018/12/06

Breakthroughs in next-generation spintronic logic and memory devices could hinge on our ability to control spin behavior in two-dimensional materials—stacks of ultrathin layers held together by relatively weak electrostatic (van der Waals) forces. The reduced dimensionality of these so-called “van der Waals materials” often leads to tunable electronic and magnetic properties, including intrinsic ferromagnetism. However, it remains a challenge to tune this ferromagnetism (e.g. spin orientation, magnetic domain phase, and magnetic long-range order) at ambient temperatures.

In this work, researchers performed a study of Fe₃GeTe₂, a van der Waals material that consists of Fe₃Ge layers alternating with two Te layers. The material’s magnetic properties were characterized using a variety of techniques, including x-ray absorption spectroscopy (XAS) with x-ray magnetic circular dichroism (XMCD) contrast at Beamline 6.3.1 and photoemission electron microscopy (PEEM) at Beamline 11.0.1.

Image: PEEM images for unpatterned and patterned Fe₃GeTe₂ samples at 110 K and 300 K. The unpatterned samples formed stripe domains at 110 K, which disappeared at 300 K. The patterned samples formed out-of-plane stripe domains at 110 K and transitioned to in-plane vortex states at 300 K, demonstrating control over magnetism at room temperature and beyond.

Extremely small magnetic nanostructures with invisibility cloak

2018/10/192018/10/25

Future data storage technology

In novel concepts of magnetic data storage, it is intended to send small magnetic bits back and forth in a chip structure, store them densely packed and read them out later. The magnetic stray field generates problems when trying to generate particularly tiny bits. Now, researchers at the Max Born Institute (MBI), the Massachusetts Institute of Technology (MIT) and DESY were able to put an “invisibility cloak” over the magnetic structures. In this fashion, the magnetic stray field can be reduced, allowing for small yet mobile bits. The results were published in Nature Nanotechnology.

For physicists, magnetism is intimately coupled to rotating motion of electrons in atoms. Orbiting around the atomic nucleus as well as around their own axis, electrons generate the magnetic moment of the atom. The magnetic stray field associated with that magnetic moment is the property we know from e.g. a bar magnet we use to fix notes on pinboard. It is also the magnetic stray field that is used to read the information from a magnetic hard disk drive. In today’s hard disks, a single magnetic bit has a size of about 15 x 45 nanometer, about 1.000.000.000.000 of those would fit on a stamp.

One vision for a novel concept to store data magnetically is to send the magnetic bits back and forth in a memory chip via current pulses, in order to store them at a suitable place in the chip and retrieve them later. Here, the magnetic stray field is a bit of a curse, as it prevents that the bits can be made smaller for even denser packing of the information. On the other hand, the magnetic moment underlying the stray field is required to be able to move the structures around.

Credit: MIT, L. Caretta/M. Huang [Source]

Magnetic vortices observed in haematite

2018/08/132018/09/03

Magnetic vortices observed in antiferromagnetic haematite were transferred into ferromagnetic cobalt.

Vortices are common in nature, but their formation can be hampered by long range forces. In work recently published in Nature Materials, an international team of researchers has used mapped X-ray magnetic linear and circular dichroism photoemission electron microscopy to observe magnetic vortices in thin films of antiferromagnetic haematite, and their transfer to an overlaying ferromagnetic sample. Their results suggest that the ferromagnetic vortices may be merons, and indicate that vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex–antivortex annihilation. Ferromagnetic merons can be thought of as topologically protected spin ‘bits’, and could potentially be used for information storage in meron racetrack memory devices, similar to the skyrmion racetrack memory devices currently being considered.

Image: Graphic outlining the antiferromagnetic rust vortices. The grayscale base layer represents the (locally collinear) magnetic order in the rust layer, and the coloured arrows the magnetic order imprinted into the adjacent Co layer.