The talk “Electrical reading-out and writing of antiferromagnetic insulators” by Lorenzo Baldrati was selected for the “Roberta Ciprian” best oral presentation award at the conference MAGNET 2019. The work demonstrates by electrical measurements and direct x-ray imaging that electrical currents can switch antiferromagnetic materials and proposes a model for the switching (https://arxiv.org/abs/1810.11326 ). L. Baldrati is currently a postdoctoral Marie Skłodowska-Curie fellow in charge of the project AntifeRromagnetic spin Transport and Switching (Twitter: #ARTES_H2020).
Benjamin Borie carried out a PhD between the group at Johannes Gutenberg-University Mainz and Sensitec as part of the EU funded Training Network WALL. He developed sensors that allow for the detection of multiple rotations.
For his work that resulted not only in commercially relevant findings but also three first author publications in leading journals he was awarded the first prize by the Chamber of Commerce.
More information can be found (in German) here [https://www.allgemeine-zeitung.de/lokales/rheinhessen/ihk-verleiht-preise-fur-spitzen-abschlusse_19903565 ].
Chamber of Commerce Representatitves award the best PhD Prizes 2018.
Our recent publication in Physical Review B entitled “Direct observation of spin diffusion enhanced nonadiabatic spin torque effects in rare-earth-doped permalloy” has been featured in the Kaleidoscope section of the journal homepage: https://journals.aps.org/prb/kaleidoscope
The work is a collaborative project with the Technical University of Kaiserslautern as part of the Spin+X collaborative research centre ( https://www.uni-kl.de/trr173/ ), and also includes data taken at the Helmholtz-Zentrum Dresden-Rossendorf.
In the paper we investigate the relationship between two important parameters for magnetization dynamics, namely the non-adiabaticity and the damping, via direct imaging of current-induced excitations of magnetic vortices in doped Permalloy discs using scanning electron microscopy with polarization analysis. We demonstrate different contributions to the enhanced non-adiabaticity in the system and show that both parameters exhibit a similar scaling with low-level rare-earth doping, providing an avenue for tailoring the dynamic properties.
The publication is available here:
Our new perspective article,” Magnetic skyrmions—Overview of recent progress in an active research field”, has been selected as the Cover Page for the latest issue of Journal of Applied Physics. In the article we highlight some of the recent developments in the field of skyrmionics, which has developed from a niche prediction to a huge and active research field within the last decade. In particular, magnetic skyrmions have become promising candidates as information carriers for next generation spintronic devices. In the piece, we describe some of the recent progress in efficiently creating and manipulating these magnetic quasiparticles and review some of the proposed device applications where skyrmions may be employed, as well as offering up our perspectives on some of the future challenges and opportunities presented by this field.
More detailed information can be found in the publication in Journal of Applied Physics at:
Congratulations to Joel Cramer who obtained a distinction in his PhD on the "Propagation, manipulation and detection of magnonic spin currents in magnetic oxides and metals". In his studies, he investigated different aspects of magnon spintronics principles, among which the magnetization-dependent detection of spin currents in a metallic ferromagnet has been published in the scientific journal Nature Communications.
In this article we determine the energetics of different topological phases in magnetic systems. We examine current‐induced generation of skyrmions in heavy‐metal/ferromagnet multilayers and show that Joule heat pulses can drive topological transitions in magnetic textures and enable skyrmion creation on nanosecond timescales. The 3D renderings for the skyrmion and domain structure of this work is featured on the front cover of the Advanced Materials journal ( https://onlinelibrary.wiley.com/toc/15214095/2018/30/49 )
We show that the antisymmetric Dzyaloshinskii-Moriya interaction is modified by driving currents. We measure and analyze the chirality of Dzyaloshinskii-Moriya-interaction (DMI) stabilized spin textures in multilayers of Ta/Co20F60B20/MgO. The effective DMI is measured experimentally using domain wall motion measurements, both in the presence (using spin-orbit torques) and absence of driving currents (using magnetic fields). We observe that the current-induced domain wall motion yields a change in effective DMI magnitude and opposite domain wall chirality when compared to field-induced domain wall motion (without current). We explore this effect, which we refer to as current-induced DMI, by providing possible explanations for its emergence, and explore the possibility of its manifestation in the framework of recent theoretical predictions of DMI modifications due to spin currents.
This is a collaborative work with the recently started group of Prof. Y. Mokrousov who is working on the theory of topological nanoelectronics and co-funded by a joint grant.
Congratulations to Kai Litzius who obtained a distinction in his PhD on the "Spin-Orbit-Induced Dynamics of Chiral Magnetic Structures". The jury was impressed with the high quality of the scientific results. Dr. Litzius is a co-author of a publication in Nature Materials dedicated to the observation of room temperature magnetic Skyrmions. Further, he revealed the Skyrmion Hall effect as reported in his first-author publication in Nature Physics.
Conventional devices using current CMOS based technologies have the unwelcome side effects of getting too hot and being limited in their speed, operating at GHz frequencies. Eventually, this is slowing down the progress of information technology. In the last years, the emerging field of “magnon spintronics” aimed at using insulating magnets capable of carrying magnetic waves, known as magnons, to solve these problems. Magnons are able to carry information at increased speeds without the production of excess heat. However, experimental observations had so far been limited to ferromagnetic materials. In collaboration with the Quantum Spintronics at NTNU and Utrecht University, our group has demonstrated that magnons can also efficiently carry spin information in antiferromagnets, the largest group of magnetic materials. This class of material has several crucial advantages over ferromagnetic components as they are stable and unaffected by external magnetic fields, a key requirement for future data storage. Additionally, antiferromagnet based devices can be potentially operated thousands of times faster than current technologies, as their intrinsic dynamics are in the THz range. As a result, antiferromagnetic magnons could thus be used in future ultra-fast and low power technological devices.
An electrical current in a platinum wire (left) creates a magnetic wave in the antiferromagnetic iron oxide (red and blue waves). This is measured as a voltage in a second platinum wire (right). The red and blue arrows represent the antiferromagnetic order of the iron oxide (© Joel Cramer)
More information can be found at: https://www.nature.com/articles/s41586-018-0490-7
Magnetic imaging allows the direct investigation of magnetic states. Especially the switching behavior of nanoscale devices is of interest because of potential future application as storage media. To image the magnetization dynamics, time-resolved imaging techniques with high spatial resolution are needed. We have accordingly developed a laboratory-based technique in cooperation with the spin-off company Surface Concept GmbH based on a commercial scanning electron microscope with polarization analysis (SEMPA). The inherent spatial resolution is <20 nm while the time resolution of the new system is better than 2 ns. To overcome the challenge of the low signal-to-noise ratio of this technique in addition a phase-sensitive detection mode was implemented for measurements with periodic excitations, where the magnetization is changing proportionally to the excitation. The research is part of the collaborative research center SPIN+X, spin in its collective environment, project B02. More information can be found at: Review of Scientific Instruments 89, 083703 (2018)
Spintronics concepts developed in modern magnetism research prevalently rely on the efficient transfer of angular momentum between interfacing subsystems. In particular, the spin information exchange between magnetically ordered insulators and conductive systems, both magnetic and non-magnetic, has been studied extensively in recent years to obtain a comprehensive understanding of the processes involved. Among others, the time scale, on which the transfer of angular momentum occurs, is decisive for the achievable data processing rates in prospective application schemes. An international team of physicists, including researchers at the Fritz Haber Institute in Berlin and the Johannes Gutenberg University Mainz, now succeeded in determining a lower time limit of the spin exchange across a magnetic insulator/metal interface. In a bilayer comprising the yttrium iron garnet Y3Fe5O12 and the heavy metal platinum, ultrafast spin current flow is generated by means of a pulsed laser heating technique. Evaluating the rise time of the spin current from detected THz responses reveal a spin correlation time of ~4 fs, implying an almost instantaneous transfer of spin informationema across the interface.
More information can be found at: Nature Communications 9, 2899 (2018)
Electric devices based on antiferromagnetic materials entail the potential to overcome the performance of conventional electronic devices in terms of speed, bit density and robustness against external magnetic fields, thanks to the particular properties of this class of materials. Such devices might be used in the future as building blocks for credit cards and devices than cannot be wiped by magnetic fields, high-speed memory and logic devices and high-capacity memory storage drives. However, at present, reading and writing bits of information electrically in antiferromagnets are challenging operations, especially in antiferromagnetic insulators, where a charge current cannot flow. In the publication “Full angular dependence of the spin Hall and ordinary magnetoresistance in epitaxial antiferromagnetic NiO(001)/Pt thin films” our group, in collaboration with the groups of J. Sinova at the JGU Mainz, E. Saitoh at the Tohoku University (Japan) and A. Kleibert at the Paul Scherrer Institute (Switzerland), has shown that it is possible to electrically read information in bilayers of antiferromagnetic NiO(001) thin films, the most stable NiO orientation, and the heavy metal Pt, by a mechanism called spin Hall magnetoresistance. We also show that strong magnetic fields (several Teslas) induce redistribution of the antiferromagnetic domains in NiO, which can be read electrically. Our results are a step toward the reliable and efficient electrical read-out of information in devices based on antiferromagnetic insulators.Additional details can be found in the publication in Physical review B, accessible at: https://link.aps.org/doi/10.1103/PhysRevB.98.024422
The poster “Current-Induced Skyrmion Generation Through Morphological Phase Transitions in Chiral Ferromagnetic Heterostructures” by Nico Kerber was selected for a best poster award at the “IEEE Magnetics Society Summer School 2018”.The work demonstrates by using high resolution x-ray microscopy that in thin films transient Joule heating can drive morphological phase transitions.
Using graphene as a light-sensitive material for light detectors can offer significant improvements with respect to materials being used nowadays. For example, graphene can detect light of almost any colour, and it gives an extremely fast electronic response within one millionth of a millionth of a second.
Published recently in Science Advances, the work gives a thorough explanation of why, in some cases, the graphene conductivity increases after light absorption and in other cases, it decreases. The researchers show that this behaviour correlates with the way in which energy from absorbed light flows to the graphene electrons: After light is absorbed by the graphene, the processes through which graphene electrons heat up happen extremely fast and with a very high efficiency.
For highly doped graphene, ultrafast electron heating leads to carriers with elevated energy – hot carriers – which, in turn, leads to a decrease in conductivity. Interestingly enough, for weakly doped graphene, electron heating leads to the creation of additional free electrons, and therefore an increase in conductivity.
More detailed information can be found in the publication in Science Advances accessible at: doi:10.1126/sciadv.aar5313
The group has received a 10.000 Euro donation by Mercedes - Benz to support work on the conversion of waste heat into useful electric energy. Compared to conventional thermoelectric cells, spin-caloritronic approaches enable possibly a simpler approach that allows for the generation of a sizeable voltage from a temperature gradient in a monolithic cell. Due to the fact that the vast majority of the energy in a conventional combustion engine is converted not into mechanical power but is lost as waste heat, such approaches are heavily investigated for industrial applications. However also the fundamental mechanisms that generate spin currents from heat currents are under heavy investigation with the important effects of the interaction of magnons and phonons being studied in detail in order to maximize the conversion efficiency.
The Marie Skłodowska-Curie individual fellowship is a competitive research grant awarded to excellent internationally-mobile young scientists by the European Union. Each fellow receives funding for 24 months, to work on his/her own research proposal. This year Dr. Lorenzo Baldrati was awarded with such a Marie Skłodowska-Curie fellowship in the Kläui lab. His fellowship adds to the ones of Dr. Romain Lebrun and Dr. Kyujoon Lee, who are already members of the same group.
The research projects of the three fellows focus on different aspects of spintronics, aiming to advance information technology by taking advantage of a property of matter related to magnetism known as “spin”. In 2016, Dr. Kyujoon Lee started his project on spin-orbit torques and Dzyaloshinskii-Moriya interactions. The following year Dr. Romain Lebrun joined the group, initiating a project on magnetization dynamics and transport in antiferromagnetic insulators. Starting this year, Dr. Lorenzo Baldrati will be working on the transport of spin currents and voltage control of antiferromagnetic materials. We are grateful to the EU for funding our Marie Skłodowska-Curie fellows in the research area of spintronics for three consecutive years.
From left to right: Dr. Romain Lebrun, Dr. Kyujoon Lee, Dr. Lorenzo Baldrati
The implementation of logic operations and thus information processing by means of spin wave (magnon) spin currents is a fundamental goal of the emerging research field of magnon spintronics. In contrast to electrical currents, on which todays information technology is based, magnon spin currents do not conduct electrical charges but magnetic momenta. So far, experimental demonstrations of magnon logic, e.g. a magnon transistor or majority gate, were based on either the manipulation or superposition of spin waves during the propagation phase. In a collaboration with the group of Prof. Ulrich Nowak from the University of Konstanz and Prof. Eiji Saitoh from the Tohoku University in Sendai, Japan, our group was now able to add a further element to the construction set of magnon logic directly at the detection site of magnon spin currents. In a ferroic spin valve structure including insulating as well as metallic ferromagnets and antiferromagnets, it was possible to demonstrate a magnon detection efficiency which depends on the magnetic configuration of the spin valve. In that manner, the suppression or transmission of the incoming magnon signal can be controlled.
More detailed information can be found in the publication in Nature Communications accessible at: doi:10.1038/s41467-018-03485-5
magnon transistors could give spintronics a boost
Focus: A Trio of Magnon Transistors
The efficient generation and detection of spin currents are in the focus of current research in the field of spintronics as they are a crucial ingredient for next-generation, energy-efficient information devices. Instead of exploiting the electron charge, information is transferred and processed by spin angular momentum. Among other techniques, the spin Hall effect and its inverse enable an effective spin-charge interconversion and furthermore the feasible integration into existing charge-based concepts. In a collaboration with the research group of Tobias Kampfrath (Freie Universität Berlin/Fritz Haber Institute of the Max Planck Society, Berlin) our group was now able to investigate the inverse spin Hall effect in copper-iridium (CuIr) alloys for various alloy compositions. We furthermore compared the spin-to-charge conversion of continuous (DC) and ultrafast (THz) spin currents. While CuIr in general reveals a complex dependence of the inverse spin Hall effect on the Ir content in the alloy, coinciding results were obtained for the DC and THz signals. The latter signifies a feasible transfer of established spintronic concepts in the ultrafast regime.
More detailed information can be found in the publication in Nano Letters at:
Felix Büttner received at the 2018 Advances in Magnetics Conference organized by the Italian Section of the IEEE the Best Young Researcher Award. He was picked from 5 finalists that were selected to present invited talks at a special Young Researchers Session of the conference based on his major achievements in the field of chiral spin structures and spin dynamics.Felix Büttner was a member of the Graduate School of Excellence Materials Science in Mainz and received his PhD at the end of 2013 on Nanomagnetism and Spin Dynamics. He is currently a postdoctoral researcher at the Massachusetts Institute of Technology.
Antiferromagnets for spin based information technology
Demonstration of technologically feasible read-out and writing of digital information in antiferromagnets –basic principle for ultrafast and stable magnetic memory
Within the emerging field of spin based electronics (spintronics), information is typically defined by the orientation of the magnetization of ferromagnets. However, recently the utilization of antiferromagnets, materials without macroscopic magnetization but with a staggered orientation of their microscopic magnetic moments (see figure), has been considered. In this framework the information is encoded in the direction of the modulation of the magnetic moments (Néel vector). In principle, antiferromagnets enable much faster information-writing and are very stable with respect to disturbing external fields. However, these advantages also imply a challenging manipulation and read-out processes of the Néel vector orientation. Up to now, this was possible using the semimetal CuMnAs only (P. Wadley et al. Science 351, 587 (2016)), a compound which features several disadvantages concerning applications such as toxic components, a relatively low magnetic ordering temperature, low conductivity and a relatively small magnetoresistance, on which the read-out of the Néel vector is based.
As published in the online science journal Nature Communications, we were now able to demonstrate current induced switching of the Néel vector also for metallic thin films of the compound Mn2Au, which order antiferromagnetically already a high temperatures. In particular, we measured a 10-fold larger magnetoresistance as observed for CuMnAs, which is explained by extrinsic scattering on excess gold atoms as deduced from calculations. By this we identified Mn2Au as a prime candidate to enable future antiferromagnetic spintronics.
More information can be found at:
Nature Communications 9, 348 (2018)
Coherent magnonic logic is an emerging field of research that allows potentially for carrying out complex computation with comparatively simple physical implementations. In contrast to incoherent logic gates, using coherent spin waves allow for using the phase degree of freedom of the spin waves. In contrast to previous approaches of exciting coherent spin waves by AC excitations, we show how the interference between superfluid spin currents that can be generated by DC excitations can endow spin circuits with coherent logic functionality. While the hydrodynamic aspects of the linear-response collective spin transport obviate interference features, we focus on the nonlinear regime, where the critical supercurrent is sensitive to the phase accumulated by the condensate in a loop geometry. We propose to control this phase by electrical gating that tunes the spin-condensate coherence length. The nonlinear aspects of the spin superfluidity thus naturally lend themselves to the construction of logic gates, uniquely exploiting the coherence of collective spin currents. Vice versa, this functionality can be used to reveal the fundamental properties of spin superfluids.
More information can be found at doi: 10.1103/PhysRevLett.119.187705
In the annual elections of the IEEE Magnetics Society, Mathias Kläui was elected as one of the 8 new members from all over the world for the Administrative Committee. The Administrative Committee is responsible for the operations of the IEEE Magnetics Society, which is the leading international professional organization for magnetism. The term is initially for three years starting 2018. Amongst other activities, the IEEE Magnetics Society organizes leading conferences, such as Intermag and publishes a range of journals on magnetism topics.
Controlling the magnetic properties of materials is fundamental for developing memory, computing and communication devices at the nanoscale. As data storage and processing are evolving quickly, researchers are testing different new methods to modify magnetic properties of materials. One approach relies on elastic deformation (strain) of the magnetic material to tune its magnetic properties, which can be achieved by electric fields. This scientific area has attracted much interest due to its potential to write small magnetic elements with a low power electric field rather than magnetic fields that require high power charge currents. However, studies so far have mainly been done at very slow time scales (seconds to milliseconds).
One way to produce rapid (i.e. subnanosecond scale) changes of strain and, thus, induce magnetization changes is by using surface acoustic waves (SAWs), which are deformation (strain) waves. In a collaboration with groups from Berlin, Switzerland and Spain where a former PhD student from our group leads this effort, we have used a new experimental technique to quantitatively image these SAW and demonstrate that they can be used to switch the magnetization in nanoscale magnetic elements on top of the crystal. Results show that the magnetic squares changed their properties under the effect of SAWs on ultra-fast timescales growing or shrinking the magnetic domains depending on the phase of the SAW.
In a more applied project, we have studied the key domain-wall properties in segmented nanowire loop-based structures used in domain-wall-based sensors. The potential of magnetic-domain-wall-based sensors is due to their many attractive attributes compared to other technologies. Magnetic domain walls can be stable well above room temperature, making them a potential candidate to store data and to be used for nonvolatile sensing, and they can be displaced rapidly in an application’s relevant geometries. The two reasons for device failure, namely, distribution of the domain-wall propagation field (depinning) and the nucleation field were determined with magneto-optical Kerr effect and giant-magnetoresistance (GMR) measurements for thousands of elements to obtain significant statistics. Single layers of Permalloy and a complete GMR stack are deposited and industrially patterned to determine the influence of the shape anisotropy, the magnetocrystalline anisotropy, and the fabrication processes. Using the GMR effect in a substantial number of devices (3000) allows us to accurately gauge the variation between devices. This measurement scheme reveals a corrected upper limit to the nucleation fields of the sensors that can be exploited for fast characterization of the working elements.
The work was carried out in collaboration with industrial partners as part of EU funded projects. In particular a long-standing collaboration with Sensitec GmbH in Mainz, where a number of previous group members work has led to major joint activities. For the collaboration including the TU Kaiserslautern the State Innovation Prize was awarded.
The publication in Physical Review Applied is available at: doi: 10.1103/PhysRevApplied.8.024017.
In the 2017 Shanghai-Ranking the Physics Department at Johannes Gutenberg University Mainz (JGU) has continued its strong performance. The ranking at positions 4-6 in Germany and in the top 75 universities in the world is mirroring the success in the German Excellence Initiative where Physics at JGU is the only department in Germany that houses both a Cluster of Excellence and a Graduate School of Excellence. In particular the resulting increasing number of high impact publications and strong international collaborations have resulted in this excellent ranking, which is also in line with the results of other rankings. More details can be found at:
We held our regular group retreat to identify new research directions and enhance collaborations at Kuralpe Kreuzhof. We have been fortunate to have Prof. E. Saitoh and Prof. G. Bauer from Tohoku University as our external experts advising us on our research program for this retreat. In addition to intense scientific work, we have also had a great time visiting the "Felsenmeer" and various sports activities.
We are happy to welcome Prof. E. Saitoh from Tohoku University for a sabbatical hosted by our group. As part of the networking activities within the collaborative research center Spin+X and the DAAD Network MaHoJeRo we are looking forward to expanding our fruitful interactions in the field of spin current physics. Prof. Saitoh is also the 2017 IEEE Distinguished Lecturer and previously staff and student exchange supported by DAAD and japanese projects has forged strong links between the groups. For recent joint work on the magnon spin valve, see arxiv:1706.07592.
Johannes Gutenberg University Mainz holds now the official Guiness World Record for the longest magnetic sphere accelerator. Initiated by the Cluster of Excellence PRISMA, a new record of 546 m was officially set. During the event, Prof. K. Wolf, State Minister for Science visited the joint information booth of the Graduate School of Excellence Materials Science in Mainz and the Collaborative Research Centre Spin + X. He was shown some of the research in materials sciences and magnetism including a superconducting railway running on magnetic tracks by Prof. M. Kläui.
The poster “Tailoring of the electrical and thermal properties using TiNiSn/HfNiSn superlattices” by Sven Heinz was selected as best poster in the Symposium H “Inorganic thermoelectrics - linking material properties and systems engineering for XXI century applications” at the Spring Meeting of the European Materials Society.
The photo shows Sven Heinz with the symposium organizers: Jan D. König, Chair of the German Thermoelectric Society, Min Gao, Sven Heinz, Marisol Martin-Gonzalez (from left to right).
The poster “Skyrmion Hall Effect Revealed by Direct Time-Resolved X-Ray Microscopy” by K. Litzius was selected as best poster at the 633rd Wilhelm und Else Heraeus-Seminar “Spin Orbit Dynamics – Connecting timescales from nanoseconds to femtoseconds”. The work showing experimentally observed highly reproducible skyrmion dynamics proofed that skyrmions can indeed reach the desired reproducibility for a spintronic device. Furthermore, the dynamics of these spin structures were investigated – showing interesting and unexpected properties.
One step ahead towards new magnetic storage devices : Fundamental research in the field of magnetic skyrmions proves suitability of thin film systems for applications and presents a new aspect of skyrmion dynamics.
The concept of a magnetic Racetrack Memory, originally proposed by Stuart Parkin (IBM/Halle) in 2008, is one of the current design ideas for future data storage devices. The conceptual device consists of a magnetic stripe, the racetrack, on which the magnetic bits are moved by current due to spin torque effects. No moving parts are required allowing for high speed and low power operation. Using magnetic skyrmions as information carriers might turn out to be a significant improvement, which could increase the data stability and reliability of the devices. In collaboration with the Massachusetts Institute of Technology (MIT), our group has demonstrated billion fold reproducible and fast skyrmion displacement due to current pulses, which is a key requirement for any application. Furthermore, the investigated dynamics turned out to be more complex than originally expected, highlighting that current theoretical descriptions are not sufficient to explain the skyrmion motion.
Furthermore, in Physical Review Letters 117, 277203 (2016) a high confidence upper bound for the enhanced non-adiabaticity of spin torque induced vortex core motion was revealed using also advanced dynamic synchrotron based imaging. The results complement and explain previously reported non-adiabaticity measurementes (PRL 105, 187203 and PRL 105, 56601). In collaboration with theoreticians the origin of this enhanced non-adiabaticity could be identified as a novel Emergent Hall Effect.
Yesterday, after three months of planning and construction, Jairo Sinova and Mathias Kläui opened the new Communication Zone. The shared communication space will be open for all members of the INSPIRE-Group, SPICE, the Kläui-Lab and their guests. The ComZone allows both groups to meet, discuss and work together on projects in a nice and modern working environment.
At the inauguration both group leaders were looking forward to even more interchange between the groups: "Whether you're just having a discussion over a cup of coffee, or a large scientific meeting, the new ComZone will be the perfect place for you. We like to thank the institute of physics for making this possible, as well as everybody who was involved in this project.
Johannes Gutenberg University Mainz was ranked in the top group of German Research Universities in Physics. In Germany a ranking in the top 5 was achieved in line with results of other rankings showing that Mainz is a leading university for Physics in Germany. More information can be found here.
The spin Seebeck effect is a spin-thermoelectric effect, which allows for harvesting waste heat in order to create spin currents in magnetic materials. These currents, when entering an adjacent metal layer, create an electrically detectable signal and can thus be used for energy or information transport. Previously we could show that the created spin currents are carried by thermally excited spin waves within the magnetic solid. Based on this discovery, material-dependent measurements as for instance the variation of the thickness of the magnetic material have revealed a direct correlation between the spin current amplitude and the intrinsic properties of the spin waves. Additionally, a clear correlation between the atomic structure of the interface between magnetic material and metal layer and the transmissivity for spin currents was determined by high resolution TEM imaging.
Furthermore, a new method to robustly determine the antisymmetric Dzyaloshinskii Moriya Interaction was published in Nano Letters. Dr. Han is joining the group as a Postdoctoral Researcher to continue to work on the DMI and use this fast throughput method to systematically understand the correlation between the materials and symmetry breaking in the systems and the resulting DMI.
Johannes Gutenberg University Mainz was ranked in the top group of European Research Universities in a number of subjects including Physics. In Germany a ranking in the top 10 was achieved in line with results of other rankings showing that Mainz is a leading university for Physics in Germany. More information can be found here.
A breakthrough in both fundamental science and technological advancement was recently achieved in collaboration with an international team of physicists from the Fritz Haber Institute, Berlin and the Johannes Gutenberg University, Mainz in realising a conceptual new source of terahertz radiation. Terahertz waves have numerous advantages from material identification; airport body scanners to bio-medical imaging as opposed to X-rays, terahertz rays are innocuous. However, there isn’t widespread use of terahertz rays primarily due to the lack of an efficient, table top broadband emitter source. Physicists at the Johannes Gutenberg University, Mainz and the Fritz Haber Institute, Berlin fabricated novel spintronics based terahertz emitters which make use of ultrafast photo-induced spin currents, the inverse spin-Hall effect and a broadband Fabry-Pérot resonance. Using the recently installed Rotating Substrate Module Ultra High Vacuum sputter deposition system from Singulus Technologies AG, a large number of multi-layered material systems were studied systematically and the terahertz emitter signal optimised. Only a few nanometers in total thickness of these new emitters are able to outperform laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and cost. Details can be found in the publication Nature Photonics DOI:10.1038/nphoton.2016.91.
A breakthrough in fundamental research in the field of potential future data storage technologies has been published in Nature Materials. The idea of the magnetic shift register, the so called Racetrack Memory, that stores information in magnetic domains was originally proposed by Stuart Parkin (IBM) in 2008. The electronic storage units (bits) should not be stored on rotating hard disks as is currently standard practice but on a nanowire. A new promising idea is to use magnetic skyrmions as information carriers on such a track, instead of conventional domains. The magnetic skyrmion bits would be rapidly accessible, while storage density would be high and there would be improved energy efficiency. In collaboration with the Massachusetts Institute of Technology (MIT), our group has managed, for the first time, to achieve targeted shifting of individual skyrmions at room temperature using electrical impulses. Details can be found in the publication Nature Materials DOI:10.1038/nmat4593 (2016).
An individual fellowship funded by the European Union through the Marie Sklodowski-Curie actions has been granted to Kyujoon Lee. He will be working on the origin of spin orbit torques and the Dzyaloshinskii-Moriya interaction, which produces particularly stable chiral spin structures. This research is also closely related to the new Collaborative Research Center (CRC) on "Spin+X: Spin in its collective environment" of Johannes Gutenberg University Mainz and the TU Kaiserslautern. These highly competitive Individual fellowships are granted to excellent researchers from abroad who want to gain experience in Europe. In addition to generous research funding, the EU program provides its fellows with the ideal environment for further research and supports the mobility of researchers within and beyond Europe.
In collaboration with an international team, our group has been able to obtain new insights into magnetic spin waves by using the Spin Seebeck effect. Recently we have been able to demonstrate that the origin of the spin Seebeck effect can be understood as thermally excited spin waves within the magnetic solid. Following now this discovery, further investigations in more complex magnetic materials, especially ferrimagnets, have been carried out. In contrast to simple ferromagnetic materials, ferrimagnets possess a non-trivial temperature dependence of the magnetization, resulting of a complex interplay of its different magnetic sublattices. By making use of temperature dependent spin Seebeck measurements of ferrimagnetic materials, it was possible to deduce characteristic and thus unique signal features. These features can be traced back to the magnonic origin of the effect and therefore allow to gain a new idea of thermal magnons and their distribution. This joint research projects involves researchers of Johannes Gutenberg University Mainz, the Walther Meißner Institute for Low Temperature Research in Garching, Tohoku University in Japan, and Delft University of Technology in the Netherlands. The resulting research paper was published in the scientific journal Nature Communications.
The Innovation Prize of Rhineland-Palatine in the category “Cooperation” was awarded to the large-scale project “Spintronic Technology Platform in Rhineland-Palatine” STeP. Within the joint project of the Technical University Kaiserslautern and the Johannes Gutenberg - University Mainz, together with Sensitec GmbH Mainz, a technology platform was created to accelerate the development of scientific results in the field of spintronics into industrial applications
The STeP Team at the Award Ceremony, from left to right: Prof. Dr. Gerhard Jakob (JGU-Mainz), Dr. Andrés Conca (TU Kaiserslautern), Dr. Frederick Casper (JGU-Mainz), minister Eveline Lemke, Prof. Dr. Matthias Kläui(JGU-Mainz), Dr. Britta Leven (TU Kaiserslautern), Dr. Marco Dorms (Sensitec), Prof. Dr. Burkard Hillebrands (TU Kaiserslautern), Dr. Johannes Paul (Sensitec), Dr. Anja Wienecke (Sensitec) and Dr. Rolf Slatter ( CEO of Sensitec GmbH ). Missing here: Dr. Ronald Lehndorff (Sensitec)
Photo: K. Müller (TU Kaiserslautern)
More information can be found here (German): http://www.uni-mainz.de/presse/74198.php
August 2015: Welcoming Japanese Guest Researchers
As part of the internationalization of our research, we are forging strong links with leading researchers in Japan and the US to study advanced spintronics concepts as part of the SpinNet project and other activities. Our spintronics groups are glad to to host a number of guest researchers from collaborating groups in Japan including Dr. Jun'ichi Ieda from JAEA Tokai who is spending a sabbatical with us. Assistant Professor Dr. T. Hajiri from Nagoya University is staying with us for alltogether 12 months as part of the Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers funded by JSPS. Mr. T. Asari received a scholarship from the Toyota Technological Institute to work with us on spin orbit torques. Dr. Y. Yamane and K. Yamamoto are working with the spintronics theory group of Prof. Sinova in Mainz. Finally one of the pioneers of the theory of spin transfer torque, Prof. G. Tatara from RIKEN is currently visiting us.
T. Asari, T. Hajiri, M. Kläui, G. Tatara, K. Yamamoto, Y. Yamane (from left to right)
J. Ieda and M. Kläui
July 2015: Publications Highlight in Nature Physics, Giant magnetoresistance systems examined by means of ultrafast terahertz spectroscopy
The forward-looking technology of spintronics now has a new, highly effective investigative instrument: German physicists from Mainz and Berlin have successfully employed ultrafast terahertz spectroscopy to determine the basic properties of spintronics components. In a joint project involving our research group and the group of Dmitry Turchinovich at the Max Planck Institute for Polymer Research in Mainz (MPI-P) and also the Mainz-based Sensitec GmbH and the Fritz Haber Institute of the Max Planck Society in Berlin, the collaborating teams were able to directly observe with ultrafast terahertz spectroscopy the magnetotransport in a ferromagnetic structure and then precisely and distinctly measure the relevant parameters, i.e., the spin-dependent charge-carrier densities and the spin-related scattering times of the conducting electrons.
February 2015: End of the successful large-scale project ”Spintronic Technology Platform in Rhineland-Palatine" STeP
”The STeP Project is a Europe-wide unique success of cooperation between Universities and industry." Vera Reiss said ”Within record time the project partners have built a bridge from basic research in the laboratories to industrial feasibility."
The project was funded by the European Regional Development Fund (ERDF), the Ministry of Science and the Ministry of Economy of Rhineland-Palatine.A press release (german) can be found here
Reference in the regional news (german, starting around 3:04)
February 2015: Publications Highlight in Nature Physics, physicists observe motion of tiny magnetic whirls
Small magnetic whirls may revolutionize future data storage and information processing if they can be moved rapidly and reliably in small structures. A team of scientists of Johannes Gutenberg University Mainz (JGU) and TU Berlin, together with colleagues from the Netherlands and Switzerland, has now been able to investigate the dynamics of these whirls experimentally. The skyrmions, as these tiny whirls are called after the British nuclear physicist Tony Skyrme, follow a complex trajectory and even continue to move after the external excitation is switched off. This effect will be especially important when one wants to move a skyrmion to a selected position as necessary in a future memory device. This research was published in the journal Nature Physics with a student of the Graduate School of Excellence Materials Science in Mainz (MAINZ) as the first author.
January 2015: ERC grants for Mathias Kläui and Martin Weides
The project combines the superconducting quantum circuits with spin waves in ferromagnets to study single magnon creation and detection. Exploring spin wave dynamics in thin films by coupling to a superconducting qubit complements conventional measurement techniques based on photon, electron or neutron scattering methods, which require highly populated excitations. The work combines magnetic materials physics is with quantum resolved spectroscopy and coherence measurements on intrinsic dynamic states.
The MultiRev ERC Proof-of-Concept grant of M. Kläui builds on the ERC Starting Grant awarded earlier and implements ideas on magnetic sensing in devices that are compatible with industrial manufacturing. Developing sensors based on magnetic domain walls opens a whole new range of sensing applications that combine non-volatility and thus low power with versatility and reliability and this development will be carried out in conjunction with leading industrial partners.
December 2014: Top ranking for Physics in Mainz
December 2014: Mathias Kläui elected Fellow of the Institute of Physics
Solid state physicist Prof. Dr. Mathias Kläui was elected to be Fellow of the Institute of Physics (IOP). IOP is the physical experts" organization of the UK and Ireland and one of the biggest international physical organizations with more than 50.000 members worldwide. The IOP elects persons to be fellows who present distinguished achievements in physics and deliver outstanding contributions. Kläui was nominated by his colleagues because of his work in the field of nanomagnetism and spin dynamic.
October 2014: Welt der Physik: Podcast | Spintronics (in German)
September 2014: Dr Chun from Korea Research Institute of Standards and Science visiting
July 2014: Mathias Kläui elected as director of the Gutenberg Nachwuchskolleg
As director of the Graduate School of Excellence Materials Science in Mainz, Mathias Kläui has broad experience in supporting PhD students.
This know-how in addition to his previous experience in support organizations for postdoctoral fellows and academies of sciences for young scientists will be used to develop support measures tailored to young scientists at Johannes Gutenberg University Mainz.
More information (in German) can be found here.
June 2014: Publications Highlight in Nature Communications
April 2014: Publications Highlight in Nature Communications
April 2014: Open Lecturer Position
In the department of physics a position of Lecturer (Vertretungsprofessur) is open. As part of the position, innovative teaching in physics as well as the organization of events of the Graduate School of Excellence Materials Science in Mainz is expected.Research in collaboration with groups in the department of Physics is possible.
Details can be found HERE.
March 2014: Publications Highlight in Nature Communications
Our recent work on holographic imaging has been published in Nature Communications (http://www.nature.com/ncomms/2014/140107/ncomms4008/full/ncomms4008.html). A new X-ray holography method was developed that will enable snap-shots of dynamic processes at highest spatial resolution. The efficiency of the new method is based on a X-ray focussing optics being firmly fixed to the object to be imaged. While this approach initially provides a blurry image, this can be focussed in the computer based on the hologram information. At the same time, the rigid connection between the object and the focussing optics elegantly solves the problem of vibration induced jitter that plays an enormous role at the nanometre scale.This work is a result of close collaboration with the group of Prof. S. Eisebitt at TU Berlin.
January 2014: Dr. Miao joins as a CSC scholar
December 2013: Christmas Party
At the end of the year the annual group christmas party took place. A guided tour of the Museum of Ancient Seafaring was followed by the traditional visit to the christmas market and then dinner at a brewery. For some the night went on in an Irish Pub...
December 2013: Visits of IEEE Distinguished Lecturers
Two awards at MORIS conference!
Benjamin Krüger wins best Poster Prize and Michael Schneider wins best Student Presentation Award at the Magnetics and Optics Research International Symposium in Omiya, Japan.The work of B. Krüger on "Inertia and chiral edge modes of a skyrmion magnetic bubble" was selected as a best poster at the Magnetics and Optics Research International Symposium (MORIS). His work explaining the dynamics of skyrmion magnetic bubble spin structures was very well received as part of the hot topic of topological spin structure dynamics. In particular the skyrmion trajectory reveals the topological winding number and the eigenfrequencies and effective mass can be deduced from the dynamics.
Furthermore Michael Schneider from the group of our collaborator S. Eisebitt at the TU Berlin won the best Student Presentation Award for his talk on our joint work on "Time resolved imaging of the gyrotropic motion of a skyrmion with 3 nanometer tracking accuracy" further highlighting the importance of this collaborative project.
November 2013: Felix Büttner obtaining a distinction in his PhD
October 2013 - Spintronics in Mainz boosted by Humboldt Professorship
September 2013: Publications Highlight in Nature Communications
August 2013: Atsushi Takeuchi appointed research scholar by the Toyota Technological Institute
June 2013: Benjamin Krüger awarded a grant from the Carl-Zeiss Foundation
May 2013 - Mathias Kläui co-chair of the Global Young Academy GA
March 2013: Amelie Axt wins a best Poster Prize at the 526th Heraeus Seminar
The work of A. Axt, A. Bisig, M. Mawass and B. Krüger on "Spin dynamics of Nanostructures on Membranes" was selected as a best poster at the 526th Heraeus Seminar on "Functional Magnetic Nanomembranes". Part of this work was also contained in A. Bisig's PhD thesis for which he received a distinction further highlighting the relevance of the topic. The work is carried out in collaboration with the group of G. Schütz and H. Stoll at the Max Planck Institute for Intelligent Systems.
February 2013: Andre Bisig obtains distinction for his PhD thesis
February 2013: Publications Highlight in Physical Review Letters
Our work on large domain wall magnetoresistance effects was recently published in http://prl.aps.org/abstract/PRL/v110/i6/e067203. We show that the Magnetoresistance in the ballistic transport regime can be governed by the presence of a domain wall at a nanoconstriction of only a few atoms cross section. Large magnetoresistance effects up to 50% induced by a domain wall are observed highlighting the importance of the atomic structure at the point contact.
February 2013: 1 Mio € DAAD Funding for Spintronics in Mainz
More information can be found in the university press release here.
January 2013: Felix Büttner wins Best Poster Award at the 12th joint Magnetism and Magnetic Materials - Intermag Conference
Recent results of the first direct dynamic imaging of single Magnetic Skyrmion Bubble domains were presented by Felix Büttner in his poster "Time-resolved Imaging of the Gyrotropic Motion of Magnetic Bubbles" at the annual 2013 Joint MMM - Intermag conference, the largest magnetism meeting in the world. At this conference in Chicago, USA he received unanimous votes as the best poster amongst more than 100 poster contributions for the exciting demonstration of the gyrating motion of skyrmionic domain structures in confined geometries. More Information on the research can be found here.Felix Büttner is a PhD student within the Graduate School of Excellence Materials Science in Mainz (MAINZ).
January 2013: Rene Röser wins Best Poster Prize at the 510th Heraeus Seminar
The work of Rene Röser and Andreas Kehlberger on "Genuine spin Seebeck effect probed by thickness dependence in YIG films" was awarded a Best Poster Prize at the 510th Heraeus Seminar on Non-Magnetic Control of Spin - Fundamental Physics and Materials Design. The work is a collaborative project between the groups of M. Kläui at Johannes Gutenberg-University Mainz and U. Nowak at the University of Konstanz within the DFG priority program "Spin Caloric Transport (SpinCaT)". Information on the research can be found here.
Andreas Kehlberger is a PhD student within the Graduate School of Excellence Materials Science in Mainz (MAINZ) and Rene Röser is carrying out his Diploma Thesis at Mainz.