Controlling tiny magnetic swirls

Research on skyrmions may lead to more effective data storage

Skyrmions, commonly imagined as tiny magnetic swirls, are nanoscale magnetic quasi-particles that have recently become a hot topic because of their potential in the development of faster and more effective data storage devices.

For the first time, an international group of scientists, with lead scientists from the Massachusetts Institute of Technology, US, and the Max-Born-Institut in Berlin  have successfully been able to observe the formation of skyrmions in a magnetic material by using ultrashort laser pulses in a magnetic material, shedding light into the microscopic process and its time period. The X-ray pulses of the European XFEL’s revealed the creation of tiny skyrmion structures on nanometer length scales at a speed which is faster than previously thought possible. The results have been published in Nature Materials.

At the atomic level, magnetic materials resemble a sea of magnetic spins in either an ‘up’ or ‘down’ orientation. These spins are linked to each other so that a single spin change will affect the orientation of other spins. Skyrmions are tiny swirl-like structures where the center spin is oppositely aligned to the spins located at its boundary with a twisted spin configuration in between. These complex spin structures are very stable and small, making them interesting candidates for future spintronic devices. Spintronics exploits both the spin and the charge of electrons that could lower energy consumption in future memory devices and data storages.

Read more on the European XFEL website

Image: A laser pulse transforms a uniform magnetization (magnetization down everywhere) to a skyrmion swirl where the magnetization in the center points up. This transformation changes the so-called topology of the system.

Credit: B. Pfau, Max Born Institute

Breaking the link between a quantum material’s spin and orbital states

The advance opens a path toward a new generation of logic and memory devices that could be 10,000 times faster than today’s.

In designing electronic devices, scientists look for ways to manipulate and control three basic properties of electrons: their charge; their spin states, which give rise to magnetism; and the shapes of the fuzzy clouds they form around the nuclei of atoms, which are known as orbitals.

Until now, electron spins and orbitals were thought to go hand in hand in a class of materials that’s the cornerstone of modern information technology; you couldn’t quickly change one  without changing the other. But a study at the Department of Energy’s SLAC National Accelerator Laboratory shows that a pulse of laser light can dramatically change the spin state of one important class of materials while leaving its orbital state intact.

>Read more on the LCLS at SLAC website

Image: These balloon-and-disk shapes represent an electron orbital – a fuzzy electron cloud around an atom’s nucleus – in two different orientations. Scientists hope to someday use variations in the orientations of orbitals as the 0s and 1s needed to make computations and store information in computer memories, a system known as orbitronics. A SLAC study shows it’s possible to separate these orbital orientations from electron spin patterns, a key step for independently controlling them in a class of materials that’s the cornerstone of modern information technology.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

New interaction between light and matter discovered at BESSY II

A German-Chinese team led by Gisela Schütz from the MPI for Intelligent Systems has discovered a new interaction between light and matter at BESSY II.

They succeeded in creating nanometer-fine magnetic vortices in a magnetic layer. These are so-called skyrmions, and candidates for future information technologies.
Skyrmions are 100 nanometre small three-dimensional structures that occur in magnetic materials. They resemble small coils: atomic elementary magnets – so-called spins – which are arranged in closed vortex structures. Skyrmions are topologically protected, i.e. their shape is unchangeable, and are therefore considered energy-efficient data storage devices.

Soft x-rays at BESSY II

In a series of experiments on the MAXYMUS beamline of BESSY II, the researchers have now shown that a bundled soft X-ray beam with a diameter of less than 50 nanometres can generate a magnetic vortex of 100 nanometres. In order to make the skyrmions visible, the researchers use the MAXYMUS scanning transmission X-ray microscope. This is a high-resolution X-ray microscope, weighing 1.8 tons, located at BESSY II.

>Read more on the BESSY II at HZB website

Image: bundled soft X-ray beam with a diameter of less than 50 nanometers writes numerous magnetic vortices, which together form the term “MPI-IS”. Credit: Alejandro Posada, Felix Groß/MPI-IS

Discovery of a novel magnetic skyrmion surface state

Skyrmions get perpendicular – and push the door open for high density data storage

Scientists from ShanghaiTech University, Diamond Light Source, the SOLEIL synchrotron and University of Oxford report in a recent issue of Nano Letters on their discovery of a novel skyrmion surface state that exists in applied in-plane fields – much different from the usual out-of-plane geometry. In this geometry, magnetic signals from the skyrmion lattice phase settle down in inconvenient reciprocal space locations, making resonant elastic X-ray scattering (REXS) on the chiral magnet Cu2OSeO3 a challenging job to carry out. By combining the complementary capabilities of the soft X-ray diffractometers at two synchrotrons (Diamond and SOLEIL) on the very same sample, the new state was unambiguously identified.

>Read more on the Diamond Light Source website

Image: Illustration of the conventional in-plane skyrmion state (a) and the novel perpendicular skyrmion state (b) in the non-centrosymmetric skyrmion system Cu2OSeO3. Whereas a conventional planar skyrmion takes up an area of A=d2 (d is the skyrmion diameter), a perpendicular skyrmion has a much reduced lateral footprint of A = w d (with w the width of the ridge) which is advantages for skyrmion memory applications. The REXS experiments were carried out in the RASOR diffractometer at beamline I10 in Diamond, and in RESOXS at the beamline SEXTANTS in Soleil (St. Aubin, France).

Dynamic pattern of skyrmions observed

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.

>Read more on the BESSY II at HZB website

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

Electric dipoles form chiral skyrmions

Control of such phenomena could one day lead to low-power, nonvolatile data storage as well as to high-performance computers.

A group of researchers, led by scientists from Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Materials Science and Engineering Department, set out to find ways to control how heat moves through materials. They fabricated a material with alternating layers of strontium titanate, which is an electrical insulator, and lead titanate, a ferroelectric material with a natural electrical polarization that can be reversed by the application of an external electric field.

When the group took the material to Berkeley Lab’s Molecular Foundry for atomic-resolution scanning transmission electron microscope (STEM) measurements, however, they found something completely unexpected: bubble-like formations had appeared throughout the material, even at room temperature.

>Read more on the ALS website

Image: (a) Hard x-ray studies showed the presence of two sets of ordering: regular peaks along the out-of-plane direction (Qz), related to superlattice periodicity (about 12 nm), and satellite peaks in the in-plane direction (Qy), corresponding to the in-plane skyrmion periodicity (about 8 nm). (b) RSXD studies were performed at the in-plane satellite peaks, which correspond to the periodic polarization texture of the skyrmions’ Bloch components. (c) Spectra from a satellite peak for right- (red) and left- (blue) circularly polarized light. (d) The same spectra with background fluorescence subtracted. (e) The difference spectrum shows a clear circular dichroism peak at the titanium L3 t2g edge.

Coherent scattering imaging of skyrmions

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.
 

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.

 

Electric skyrmions charge ahead for next-generation data storage

Berkeley Lab-led research team makes a chiral skyrmion crystal with electric properties; puts new spin on future information storage applications.

When you toss a ball, what hand do you use? Left-handed people naturally throw with their left hand, and right-handed people with their right. This natural preference for one side versus the other is called handedness, and can be seen almost everywhere – from a glucose molecule whose atomic structure leans left, to a dog who shakes “hands” only with her right.

Handedness can be exhibited in chirality – where two objects, like a pair of gloves, can be mirror images of each other but cannot be superimposed on one another. Now a team of researchers led by Berkeley Lab has observed chirality for the first time in polar skyrmions – quasiparticles akin to tiny magnetic swirls – in a material with reversible electrical properties. The combination of polar skyrmions and these electrical properties could one day lead to applications such as more powerful data storage devices that continue to hold information – even after a device has been powered off. Their findings were reported this week in the journal Nature.

>Read more on the Advanced Light Source website

Image: Simulations of skyrmion bubbles and elongated skyrmions for the lead titanate/strontium titanate superlattice.
Credit: Berkeley Lab.

Diamond celebrates publication of its 7000th paper

A paper in PNAS by an international scientific collaboration from the UK, Germany and Switzerland is the 7000th to be published as a result of innovative research conducted at Diamond Light Source, the UK’s Synchrotron.

This new paper reveals details of the 3D spin structure of magnetic skyrmions, and will be of key importance for storing digital information in the development of next-generation devices based on spintronics.

Laurent Chapon, Diamond’s Physical Sciences Director, explains the significance of these new findings:  “A skyrmion is similar to a nanoscale magnetic vortex, made from twisted magnetic spins, but with a non-trivial topology that is ‘protecting them’. They are therefore stable, able to move, deform and interact with their environment without breaking up, which makes them very promising candidates for digital information storage in next-generation devices. For years, scientists have been trying to understand the underlying physical mechanisms that stabilise magnetic skyrmions, usually treating them as 2D objects. However, with its unique facilities and ultra-bright light, Diamond has provided researchers the tools to study skyrmions in 3D revealing significant new data.”

As spintronic devices rely on effects that occur in the surface layers of materials, the team was investigating the influence of surfaces on the twisted spin structure. It is commonly assumed that surface effects only modify the properties of stable materials within the top few atomic layers, and investigating 3D magnetic structures is a challenging task. However, using the powerful circularly polarised light produced at Diamond, the researchers were able to use resonant elastic X-ray scattering (REXS) to reconstruct the full 3D spin structure of a skyrmion below the surface of Cu2OSeO3.

>Read more on the Diamond Light Source website

Image: (extract) Illustration of a ‘Skyrmion tornado’. The skyrmion order changes from Néel-type at the surface to Bloch-type deeper in the sample. On the right hand side, the corresponding stereographic projections of these two boundary skyrmion patterns are shown. Full image and detailed article here.

A surprising twist on skyrmions

Magnetic tomography has been used to reconstruct a tornado-like 3D magnetic skyrmion structure.

Vortex structures are common in nature, reaching from swirls in our morning coffee to spiral galaxies in the universe. Vortices are been best known from fluid dynamics. Take the example of a tornado. Air circulates around an axis, forming a swirl, and once formed, the twisted air parcels can move, deform, and interact with their environment without disintegrating. A skyrmion is the magnetic version of a tornado which is obtained by replacing the air parcels that make up the tornado by magnetic spins, and by scaling the system down to the nanometre scale. Once formed, the ensemble of twisted spins can also move, deform, and interact with their environment without breaking up ‒ the ideal property for information carriers for memory and logic devices.

What makes a tornado stable is not only coming from its twist, but also due to its three-dimensional properties, i.e., the wind current has extra twist along the column of turbulent flow. This leads to a tight bundling of the vortex sheets at different heights along the tornado column. Similarly, such a 3D structure can also occur in magnetic skyrmions, guaranteeing their topological stability. Up to now, skyrmions have been most commonly treated as two-dimensional objects, and their exciting tornado-like structure remained unexplored. In fact, the 3D characterization of magnetic structures is a rather challenging task. A team of researchers, led by the University of Oxford and Diamond Light Source, have used the energy-dependence of resonant elastic X-ray scattering (REXS) on beamline I10 at Diamond to measure the microscopic depth dependence of ‘skyrmion tornados’ in Cu2OSeO3. In their work, published in Proceedings of the National Academy of Sciences, they reveal a continuous change from Néel-type winding at the surface to Bloch-type winding in the bulk with increasing depth. This not only demonstrates the power of REXS for microscopic studies of surface-induced reconstructions of magnetic order, but also reveals the hidden energetics that makes magnetic skyrmions such a stable state – a crucial finding for skyrmion device engineering.

>Read more on the Diamond Light Source website

Figure: Illustration of a ‘Skyrmion tornado’. The skyrmion order changes from Néel-type at the surface to Bloch-type deeper in the sample. On the right hand side, the corresponding stereographic projections of these two boundary skyrmion patterns are shown.