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.
Excellent ranking of Mainz in Nature Index Ranking 2016
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.
July 2016: Publication highlights in Physical Review X and Nano Letters
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.
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