It is known that magnetization can be manipulated by short light pulses but so far the spatially - resolved magnetization change could not be determined due to the limited spatial resolution of conventional optical techniques. Since most of the ferromagnetic materials consist of multiple domains with different magnetization directions, the local change of the magnetization in these domains and at the interfaces between the domains (domain walls) is of particular interest. At the FLASH free electron laser at the DESY Research Center in Hamburg, results were obtained that are in agreement with a recently theoretically predicted mechanism: due to the laser pulses, highly excited electrons are generated that move quickly through the material. They thus move from one domain into a neighboring domain with a different magnetization direction. Since the electrons carry part of the magnetization, they manipulate the magnetization in the domains as they move across a domain wall. This means, domain walls can change their profile on the fs time scale.
The experiments were carried out in a collaboration with researchers from the TU Berlin, the University of Hamburg, Paris and six further research institutes at the free electron laser FLASH at DESY in Hamburg.
Yenny Hernandez was appointed assistant professor (tenure track) at Universidad de los Andes - Bogota from August 1st. She will leave our group but continue to work on carbon structures and collaborate with our group in particular on turbostratic graphitic microstructures.Congratulations and good luck to her.
Prof. Tetsuya Miyawaki from Nagoya University is visiting the group as a guest Professor as part of a collaboration on iron based Heusler compounds. High resolution magnetic imaging is being used to study the advanced thin film structures prepared in Nagoya and ascertain the magnetic properties. As part of a long term joint project, the growth expertise in Nagoya is combined with the magnetic imaging know-how at Mainz.
The physics department of the University of Mainz is one of the most successful in obtaining third party funding from the German Science Foundation.
Mainz has the 6th largest total DFG project funding and is number 3 for funding when excluding excellence initiative projects.
The German Science Foundation announced that the application for the Graduate School of Excellence "Materials Science in Mainz" was successful with an increased budget. With this prolongation under the new director Mathias Kläui, the successful research and training program in Materials Science will be continued and further developed including strengthening new research areas.
The graduate school is a collaborative project between the Johannes Gutenberg-University of Mainz, the Kaiserslautern University of Technology and the Max Planck Institute for Polymer Research.
More details about the Graduate School can be found at www.mainz.uni-mainz.de
Furthermore the Cluster of Excellence Precision Physics, Fundamental Interactions and Structure of Matter was also granted making the Physics department at Mainz one of the most successful in Germany.
Hubertus Braun has been awarded the Vodafone Support Prize 2012 of the Vodafone foundation for his master thesis on
,Glass ceramics with paraelectric phases for mobile applications in the GHz rangeâ, which was carried out under the supervision of Gerhard Jakob.
The prize ceremony took place in the Albertinum in Dresden.
More information can be found here.
The work of Felix Büttner on Magnetic Soliton Dynamics was presented as a poster "New soft high anisotropy materials for magnetization dynamics of solitonic spin structures" at the 2012 International Magnetics Conference (Intermag) in Vancouver, Canada. His contribution was selected from more than 100 posters for the high scientific quality as well as the presentation.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).
Prof. Tetsuya Miyawaki from Nagoya University is staying in the group as a guest Professor. Prof. Miyawaki is a specialist on iron based Heusler compounds. Combining the know-how on the preparation of high quality thin films with the magnetotransport expertise in the group will be used to study the prospect of using these compounds in spintronics devices.
Christian Mix has co-organized a symposium on Spintronics on the way to modern storage technology. The idea to solicit proposals for a symposium from PhD students for PhD students is a joint initiative of the magnetism division and the young DPG. The symposium is a special session of the DPG Spring meeting in Berlin, March 25-30, 2012.
Dr. Thomas Moore is a lecturer at the University of Leeds who is currently visiting the group funded by the Alexander von Humboldt Foundation. Dr. Moore works on spin torque and spin orbit effects in high anisotropy materials without inversion asymmetry leading to strong Rashba fields. Dr. Moore has a longstanding tradition of working with the group with two joint publications in Physical Review Letters in the last two years.
Simone Finizio joined us as a PhD student after being successful in the last round of the competition for the Graduate School of Excellence Materials Science in Mainz (MAINZ). Simone recently passed his Master at the Politecnico di Milano with the top grade and joins us to work on spin and charge dynamics in oxidic nanostructures.
The work is performed as part of a project in the DFG funded priority program "Graphene".
Change of microstructure and shape of solid materials by external magnetic fields
Congratulations to Felix Büttner who was selected as a member of the graduate school of excellence Materials Science in Mainz (MAINZ). The jury commended his work on ultrafast magnetization manipulation and the further development of the x-ray holography technique.
More information can be found here.
The racetrack memory device was envisaged by Stuart Parkin at the Almaden IBM research center (US Patent 6 834 005 and Science 320, 190 (2008)). In this device, the information is stored as magnetic domains delineated by a domain wall. This principle is similar to magnetic tape (such as a video cassette) but in contrast to tape where the information is physically moved with the tape, in the racetrack the information is moved inside the tape by injecting spin polarized currents and the racetrack stays fixed with no mechanical motion. A layman's description (in german) can be found in Physik in unserer Zeit.
In our work, we have investigated the underlying physics that allows for the displacement of domains and domain walls. This so-called spin transfer torque leads to a motion of the domains and domain walls in the electron flow if a spin-polarized current is injected. The speed is governed by the non-adiabaticity parameter, which characterizes the spin polarized charge carrier transport across a spin texture such as a domain wall. By measuring the displacement of a vortex core in a magnetic disc, we find that for these vortex cores the non-adiabaticity parameter is larger than expected and from this one could deduce possible velocities for domain walls including vortices that are higher than those currently measured. We have found using an independent method that vortices in vortex walls exhibit the same high non-adiabaticity (Physical Review Letters 105, 56601 (2010)) as found for the vortices in discs in this work.
Since it is the speed of the domain walls that governs the access (read/write) times of the device, this would make the racetrack a formidable competitor as a non-volatile memory device.