spintronics – Lightsources.org

Ultrafast all-optical spin injection in silicon revealed at FERMI

2022/11/282022/11/29

A revolutionary and energy-efficient information technology encoding digital data in electron spin (spintronics) by combining semiconductors and ferromagnets is being developed worldwide. Merging of memory and logic computing of magnetic based storage devices and silicon-based logic transistors is expected to ultimately lead to new computing paradigms and novel spin-based multifunctional devices. The advantages of this new technology would be non-volatility, increased data processing speed, reduced electric power consumption. All of them are essential steps towards next generation quantum computers.

To create spin-based electronics with potential to revolutionize information technology, silicon, the predominant semiconductor, needs to be integrated with spin functionality. Although silicon is non-magnetic at equilibrium, spin polarized currents can be established in Si by a variety of approaches such as the use of polarized light, hot electrons spin injection, tunnel spin injection, Seebeck spin tunneling and dynamical spin pumping methods, as had been demonstrated recently. In general, spin polarized currents refer to the preferential alignment of the spin angular momentum of the electrons in a particular direction.

Spintronics: A new tool at BESSY II for chirality investigations

2022/10/242022/11/09

Information on complex magnetic structures is crucial to understand and develop spintronic materials. Now, a new instrument named ALICE II is available at BESSY II. It allows magnetic X-ray scattering in reciprocal space using a new large area detector. A team at HZB and Technical University Munich has demonstrated the performance of ALICE II by analysing helical and conical magnetic states of an archetypal single crystal skyrmion host. ALICE II is now available for guest users at BESSY II.

The new instrument was conceived and constructed by HZB physicist Dr. Florin Radu and the technical design department at HZB in close cooperation with Prof. Christian Back from the Technical University Munich and his technical support. It is now available for guest users at BESSY II as well.

“ALICE II has an unique capability, namely to allow for magnetic X-ray scattering in reciprocal space using a new large area detector, and this at up to the highest allowed reflected angles”, Radu explains. To demonstrate the performance of the new instrument, the scientists examined a polished sample of Cu₂OSeO₃.

Read more on the HZB website

Image: The picture reflects the main effect measured with a newly developed instrument ALICE II at BESSY II: A circular polarised soft-X-ray beam scatters off a crystal that exhibits a helical or conical magnetic order. This leads to two scattered beams of different intensity. The difference in intensity of these scattered beams is a measure of the chirality of the equidistant magnetic helices.

Credit: © F. Radu/HZB

A light-induced spin switching device with promising applications in spintronics

2022/10/192022/11/16

A research work led by the University of Valencia (Spain) has reported the fabrication of a novel device that allows the robust electrical detection of a fast and effective light-induced and thermally induced spin transition with an outstanding performance. It represents a tool with promising potential for generating new systems with applications in spintronics and straintronics. Experiments carried out at the BOREAS beamline have been crucial in this study.

The search for more efficient data transport and storage methodologies has helped the development of new research areas, such as molecular spintronics. This novel discipline uses molecular compounds as functional materials in a new generation of devices in which the information tool used is not only the charge (electrons) transport but also the spin. The spin is an intrinsic property of electrons (as mass or electric charge). By adding this new variable of information transport, it is possible to create more efficient electronic devices with a larger capacity for data processing.

There is an increasing demand for discovering new compounds that are functional for spintronics and allow for industrial scalability in its processing. Sublimable spin-crossover (SCO) molecules are compounds of great interest in this matter. These materials can switch between two states called low-spin and high-spin, depending on a variety of external stimuli such as light or temperature. More specifically, compounds based on iron (II) present opposite magnetic properties between both states; paramagnetic in high-spin and diamagnetic in low-spin.

In a novel study published in the journal Advanced Materials, researchers from the Molecular Science Institut (ICMol) from the University of Valencia (UV) in Spain, in collaboration with members from the BOREAS beamline at the ALBA Synchrotron, have developed spin-crossover/graphene hybrid devices by incorporating films of an iron (II) based material, with the properties aforementioned, in its metastable crystallographic phase. Previously thought to be inert regarding spin-crossover, the work developed at the BOREAS beamline has allowed the discovery of interesting thermal and light-induced spin transition capabilities that this crystallographic phase does show when appropriately isolated.

Read more on the ALBA website

Giant Rashba semiconductors show unconventional dynamics with potential applications

2022/07/062022/07/15

Germanium telluride is a strong candidate for use in functional spintronic devices due to its giant Rashba-effect. Now, scientists at HZB have discovered another intriguing phenomenon in GeTe by studying the electronic response to thermal excitation of the samples. To their surprise, the subsequent relaxation proceeded fundamentally different to that of conventional semimetals. By delicately controlling the fine details of the underlying electronic structure, new functionalities of this class of materials could be conceived.

In recent decades, the complexity and functionality of silicon-based technologies has increased exponentially, commensurate with the ever-growing demand for smaller, more capable devices. However, the silicon age is coming to an end. With increasing miniaturisation, undesirable quantum effects and thermal losses are becoming an ever-greater obstacle. Further progress requires new materials that harness quantum effects rather than avoid them. Spintronic devices, which use spins of electrons rather than their charge, promise more energy efficient devices with significantly enhanced switching times and with entirely new functionalities.

Spintronic devices are coming

Candidates for spintronic devices are semiconductor materials wherein the spins are coupled with the orbital motion of the electrons. This so-called Rashba effect occurs in a number of non-magnetic semiconductors and semi-metallic compounds and allows, among other things, to manipulate the spins in the material by an electric field.

First study in a non equilibrium state

Germanium telluride hosts one of the largest Rashba effects of all semiconducting systems. Until now, however, germanium telluride has only been studied in thermal equilibrium. Now, for the first time, a team led by HZB physicist Jaime-Sanchez-Barriga has specifically accessed a non-equilibrium state in GeTe samples at BESSY II and investigated in detail how equilibrium is restored in the material on ultrafast (<10^-12 seconds) timescales. In the process, the physicists encountered a new and unexpected phenomenon.

First, the sample was excited with an infrared pulse and then measured with high time resolution using angle-resolved photoemission spectroscopy (tr-ARPES). “For the first time, we were able to observe and characterise all phases of excitation, thermalisation and relaxation on ultrashort time scales,” says Sánchez-Barriga. The most important result: “The data show that the thermal equilibrium between the system of electrons and the crystal lattice is restored in a highly unconventional and counterintuitive way”, explains one of the lead authors, Oliver Clark.

Read more on the HZB website

Image: Left: Electronic structure of GeTe taken with 11 eV photons at BESSY-II, showing the band dispersions of bulk (BS) and surface Rashba states (SS1, SS2) in equilibrium. Middle: Zoom-in on the region of the Rashba states measured with fs-laser 6 eV photons. Right: Corresponding out-of-equilibrium dispersions following excitation by the pump pulse.

A magnetic nano-elevator for spintronic devices

2022/05/272022/06/01

Researchers propose and demonstrate for the first time a new concept for the transfer of magnetic data in three dimensions based on geometrical effects for the interconnection of functional spintronic planes. The device is based on a magnetic nanostructure and promotes the spontaneous motion of bits without the need to apply any external stimuli. This work has promising applications in spintronics. Experiments at the CIRCE beamline in ALBA were key to characterize the magnetic structures and confirm their functioning.

Information technologies will be responsible for about 20% of electricity consumption worldwide by 2025, which urgently requires the development of new types of greener nanoelectronic devices. Spintronics, making use of not only the charge of electrons but also of its intrinsic angular momentum (its spin) is an emerging technology that can overcome some of these challenges, thanks to its non-volatility character, full compatibility with CMOS (complementary metal-oxide-semiconductor), low and fast write/reading processes, and high endurance.

However, as nanoelectronic devices move towards denser forms exploiting three dimensions, new mechanisms to efficiently interconnect functional planes become necessary. The shift to 3D devices should enable ultra-highly dense storage and memory devices, but their realization brings huge challenges, from their fabrication to their interconnection or effective heat dissipation.

Read more on the ALBA website

Image: PEEM magnetic nano-elevator

Disorder brings out quantum physical talents

2021/09/012021/09/07

Quantum effects are most noticeable at extremely low temperatures, which limits their usefulness for technical applications. Thin films of MnSb₂Te₄, however, show new talents due to a small excess of manganese. Apparently, the resulting disorder provides spectacular properties: The material proves to be a topological insulator and is ferromagnetic up to comparatively high temperatures of 50 Kelvin, measurements at BESSY II show. This makes this class of material suitable for quantum bits, but also for spintronics in general or applications in high-precision metrology.

Quantum effects such as the anomalous quantum Hall effect enable sensors of highest sensitivity, are the basis for spintronic components in future information technologies and also for qubits in quantum computers of the future. However, as a rule, the quantum effects relevant for this only show up clearly enough to make use of them at very low temperatures near absolute zero and in special material systems.

Read more on the HZB website

Image: The Dirac cone is typical for topological insulators and is practically unchanged on all 6 images (ARPES measurements at BESSY II). The blue arrow additionally shows the valence electrons in the volume. The synchrotron light probes both and can thus distinguish the Dirac cone at the surface (electrically conducting) from the three-dimensional volume (insulating).

Credit: © HZB

Scientists streamline process for controlling spin dynamics

2021/01/182021/01/19

Marking a major achievement in the field of spintronics, researchers at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Yale University have demonstrated the ability to control spin dynamics in magnetic materials by altering their thickness. The study, published on the 18th January in Nature Materials, could lead to smaller, more energy-efficient electronic devices.

“Instead of searching for different materials that share the right frequencies, we can now alter the thickness of a single material—iron, in this case—to find a magnetic medium that will enable the transfer of information across a device,” said Brookhaven physicist and principal investigator Valentina Bisogni.

Read more on the BNL website

Image: An artist’s interpretation of measuring the evolution of material properties as a function of thickness using resonant inelastic x-ray scattering.

Germanium telluride’s hidden properties revealed

2020/11/052020/11/10

Germanium Telluride is an interesting candidate material for spintronic devices. In a comprehensive study at BESSY II, a Helmholtz-RSF Joint Research Group has now revealed how the spin texture switches by ferroelectric polarization within individual nanodomains.

Germanium telluride (GeTe) is known as a ferrolectric Rashba semiconductor with a number of interesting properties. The crystals consist of nanodomains, whose ferrolectric polarization can be switched by external electric fields. Because of the so-called Rashba effect, this ferroelectricity can also be used to switch electron spins within each domain. Germanium telluride is therefore an interesting material for spintronic devices, which allow data processing with significantly less energy input.

Russian German Cooperation

Now a team from HZB and the Lomonosov Moscow State University, which has established a Helmholtz-RSF Joint Research Group, has provided comprehensive insights into this material at the nanoscale. The group is headed by physical chemist Dr. Lada Yashina (Lomonosov State University) and HZB physicist Dr. Jaime Sánchez-Barriga. “We have examined the material using a variety of state-of-the-art methods to not only determine its atomic structure, but also the internal correlation between its atomic and electronic structure at the nanoscale,” says Lada Yashina, who produced the high-quality crystalline samples in her laboratory.

Read more on the BESSY II website

Image: The Fermi surface of multidomain GeTe (111) bulk single crystal measured with high-resolution angle-resolved photoemission at BESSY II. © HZB

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

Towards oxide-integrated epitaxial graphene-based spin-orbitronics

2018/09/272018/09/28

An international team of researchers from IMDEA Nanociencia and Complutense and Autónoma universities in Madrid, the Institut Néel in Grenoble and the ALBA Synchrotron in Barcelona has elucidated a new property of Graphene/Ferromagnetic interfaces: the existence of a sizable magnetic unidirectional interaction, technically a Dzyaloshinskii–Moriya Interaction of Rashba origin, which is responsible for establishing a chiral character to magnetic domain wall structures.

A major challenge for future spintronics is to develop suitable spin transport channels with long spin lifetime and propagation length. Graphene can meet these requirements, even at room temperature. On the other side, taking advantage of the fast motion of chiral textures, that is, Néel-type domain walls and magnetic skyrmions, can satisfy the demands for high-density data storage, low power consumption, and high processing speed. The integration of graphene as an efficient spin transport channel in the chiral domain walls technology depends on the ability to fabricate graphene-based perpendicular magnetic anisotropy (PMA) systems with tailored interfacial SOC.

Studies on graphene-based magnetic systems are not abundant and, typically, make use of metallic single crystals as substrates which jeopardize the exploration of their transport properties (since the current is drained by the substrate). To solve this challenge, the IMDEA Nanociencia leading team succeeded to fabricate high-quality epitaxial asymmetric gr/Co/Pt(111) structures grown on (111)-oriented oxide substrates. The quality of the interfaces was checked by low-energy electron diffraction and also by advanced high-resolution transmission microscopy at the Universidad Complutense de Madrid (UCM) microscopy centre and resonant X-ray specular reflectivity at BOREAS beamline at ALBA (see fig.1). The magnetic anisotropy and properties were investigated by magneto-optical Kerr magnetometry in IMDEA and Universidad Autónoma de Madrid (UAM) and complemented with element resolved XMCD magnetometry also at BOREAS beamline. Finally, the chirality of the magnetic domain walls was analysed using a customized magneto-optical Kerr effect microscope and pulse field electronics in collaboration with the team at Institut Néel in Grenoble.

>Read more on the ALBA website

Diamond celebrates publication of its 7000th paper

2018/07/032018/07/04

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.

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.

Ferromagnetic and antiferromagnetic coupling of spin molecular interfaces

2018/05/282018/05/31

Researchers from the physics department of the Università “La Sapienza” in Rome, Centro S3 of Modena and ALBA, have demonstrated that magnetic coupling of metal-organic molecules to a magnetic substrate mediated by a graphene layer can be tuned in strength and direction by choosing the symmetry of the molecular orbitals that is largely preserved thanks to the graphene layer. The results have been published in the journal Nano Letters.

Paramagnetic molecules become potential building blocks in spintronics when their magnetic moments are stabilized against thermal fluctuations, for example, by a controlled interaction with a magnetic substrate. Spin molecular interfaces with preserved magnetic activity and exhibiting magnetic remanence at room temperature (RT) can open the route to engineer highly spin-polarized, nanoscale current sources. The need to fully control the organic spin interface and the tuning of ferromagnetic (FM) or antiferromagnetic (AFM) coupling to achieve a stable conductance has motivated a vast experimental interest.

>Read more on the ALBA website

Image: Figure 1: a,b) Antiferromagnetic/Ferromagnetic coupling as deduced by element-specific hysteresis loops of a FePc and CuPc (respectively) to a Cobalt layer with perpendicular magnetic anisotropy intercalated below graphene. c,d) orbital-porjection of the spin-density for the FePc and CoPc interface reflecting the different symmetry of the molecular orbitals involved in the ferromagnetic and antiferromagnetic interaction.

Researchers obtain nanometric magnetite with full properties

2018/03/142018/03/15

When reducing materials at the nanoscale, they typically lose some of their properties. The experiments have been carried out at the CIRCE beamline of the ALBA Synchrotron.

Magnetite is a candidate material for various applications in spintronics, meaning that can be employed in devices where the spin of the electron is used to store or manipulate information. However, when it is necessary to create structures of the material at the nanometric scale, their properties get worse. A study, recently published in the scientific journal Nanoscale, has proved that, with suitable growth, magnetite could be used to create nanostructured magnetic elements without losing their properties.

“Oxides have been proposed to be used for spin waves in triangular structures for computing. And our results suggest that magnetite could be used for this purpose, “says Juan de la Figuera, scientist from the Spanish National Research Council (CSIC).

>Read more on the ALBA website

Image: Beamline involved where nanometric magnetite has been obtained, keeping its full properties.
Credit: ALBA

Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking

2017/10/202018/01/16

Research collaboration led by Professor Philip King from University of St. Andrews, and comprising the researchers from Max Planck Institute for Chemical Physics of Solids in Dresden, Institute for Theoretical Physics of the University of Heidelberg and researchers from I05 beamline at Diamond Light Source and APE beamline at Elettra, described a new route to maximise the spin-splitting of surface states.
The electronic properties of surfaces are often different from those of the bulk. In particular, the intrinsically broken symmetries of the surface compared with the bulk of the material allow for appearance of the new electronic surface states. For the systems in which spin-orbit interaction is strong, a non-negligible separation of these states according to their spin takes place. The spin splitting of surface- or interface-localized two-dimensional electron gases is characterized by a locking of the electron spin perpendicular to its momentum.

Time – and spatially – resolved magnetization dynamics driven by spin-orbit torques

2017/10/172018/01/17

There is a strong correlation between the rise of a civilization and writing. The so-called Information Age developed in parallel with the ability to write, store, and process large amounts of digital data. To keep pace with the increasing demand for data of our days, not only the size but also the speed of digital memories must increase dramatically, while keeping the energy consumption at reasonable levels. In order to achieve that, we must learn to write anew.

>Read More on the PSI website

Image: Magnetisation switching of a 500 nm diameter Pt/Co/AlOx disc.