Highlights 2016


Doctoral graduation in the ATFT group

© Gabi Haindl

It is a big pleasure to congratulate our dear colleague Aldin Radetinac to his doctorate defense. His work entitled: Thin film growth and investigation of the application potential of SrMoO3 was awarded the highest honors (summa cum laude) by the doctoral commission (December 2nd, 2016). The defense was followed by a perfectly prepared party with delicious home-made food. We thank Dr. Radetinac not only for this memorable day, but for his outstanding contributions to the group. We are happy that Aldin continues to work in our group driving his scientific work more into the realm of application within a 1.5-million Euro project funded by the German Federal Ministry of Education and Research (BMBF) through the program VIP+. Aldin’s publication list includes more than 16 entries and one patent pending. Congratulations and all the best!

Award for excellent teaching: TU Darmstadt grants Athene-award

Die Athene-Preisträger des Sonderpreises Interdisziplinäre Lehre. – © Foto: Claus Völker
The awardees of the special award for Interdisciplinary Science 2016. Foto: Claus Völker

The Athene-awards for excellent teaching granted by the Carlo and Karin Giersch-Fellowship at TU Darmstadt in the amount of 40000 Euro have been presented on November 24th to the winners that have collected special merits for excellent teaching: The award ceremony is the traditional end of TU Darmstadt’s “Teaching Day” (Tag der Lehre).

The special award for Interdisciplinary Teaching in the amount of 3000 Euro was awarded to Prof. Dr.-Ing. Volker Hinrichsen, Prof. Dr. Lambert Alff, Prof. Dr. Petra Gehring, Prof. Dr. Norbert Pietralla, Prof. Dr. Gerhard Thiel and Prof. Dr. Stefan Ulbrich for the extremely successful interdisciplinary lecture series „What’s behind all this?“ („Was steckt dahinter?“), where TU scientists report on their background, motivation, and research in a way understandable to listeners from all faculties and to interested members of the public.

Featured article in APL Materials (open access):

Engineering perpendicular magnetic anisotropy in Fe via interstitial nitrogenation: N choose K

Hongbin Zhang, Imants Dirba, Tim Helbig, Lambert Alff, and Oliver Gutfleisch

APL Mater. 4, 116104 (2016)

This study is product of the collaboration of three groups within the LOEWE project RESPONSE. In the paper, combining experimental results and first principles calculations, we show that interstitial nitrogen not only serves for inducing tetragonality in α′-Fe8Nx but is also essential for achieving a high degree of perpendicular magneto-crystalline anisotropy, K. Our results demonstrate that the orbital magnetic moments of the iron atoms above and below N in the direction of magnetization are much more susceptible to the applied magnetic field than their in-plane counterparts, leading to a giant value of K as compared to a hypothetical distorted material without N.

doi: 10.1063/1.4967285

Impact of oxygen stoichiometry on electroforming and multiple switching modes in TiN/TaOx/Pt based ReRAM

S. U. Sharath, M. J. Joseph, S. Vogel, E. Hildebrandt, P. Komissinskiy, J. Kurian, T. Schroeder and L. Alff

Appl. Phys. Lett. 109, 173503 (2016)

In collaboration with the IHP (Leibniz-Institute for Innovations for High Performance Microelectronics) we have published a study on resistive random access memory (RRAM). The study is based on oxygen engineered TaOx where the concentration of oxygen vacancies can be controlled leading to adjustable forming voltages. A stable bipolar resistive switching (BRS) occurs in all devices irrespective of oxygen content, unipolar switching was found to coexist with BRS only at higher oxygen contents, which transforms to a threshold switching behavior in devices grown under highest oxidation. The study clarifies the correlation between materials parameters such as oxygen stoichiometry and electrical performance such as the switching behavior. The work was funded by DFG and EU (PANACHE) .

doi: 10.1063/1.4965872

Review article about 112 pnictide superconductors

doi: 10.1002/pssb.201600163
doi: 10.1002/pssb.201600163

A review article summarizing the state of knowledge about so called 112 pnictides, a new class of high-temperature superconductors, has appeared in Phys. Status Solidi B. Soumya Ray is the first author of this article who meanwhile accepted a position at the Indian Institute of Technology (IIT) in Patna. Substitution of Arsenic by Antimony might be a way to boost the critical temperature in the pnictide superconductors beyond the value of 77 K which is the boiling temperature of liquid nitrogen. Besides superconductivity, the material class offers also compounds which are similar in some properties to graphene. The work has been performed within a DFG funded priority programme SPP 1458.

doi: 10.1002/pssb.201600163

8th Joint European Magnetic Symposion (JEMS)

The city of Glasgow in Scotland hosted the 8th JEMS (Joint European Magnetic Symposia) conference from 21st to 26th of August 2016 organized by the Institute of Physics (IOP) with more than 600 participants. Since 15 years, the Joint European Magnetic Symposia as the most important and comprehensive conference on magnetism in Europe presenting the latest developments in magnetism and magnetic materials research. The presented topics included a wide range of current research areas such as materials for energy applications, spintronics, ultrafast optical switching, chiral spin materials and magnonics. This year from ATFT group, a Ph.D. student (Sareh Sabet) had the opportunity to participate in this exciting scientific event and presented the results of her ongoing research on structural and magnetic properties of c-axis oriented MnBi thin films with high anisotropy grown from a single Mn55Bi45 sputtering target.

Merck-Run and “Klassenerhalt” of the fleur-de-lis – Good bye to Marco “Toni” Sailer

© Lambert Alff

This May had two memorable sports events. ATFT participated with several teams in the “Darmstädter Merck-Firmenlauf” in the categories 5 km and 10 km. As you can see, the After-Run-Party was a lot of fun – but unfortunately the beer was not the only humidity that day… After “Energiewende”, the international world had to learn a new German word: “Klassenerhalt”. The soccer team of Darmstadt in the German Bundesliga was able to stay in the league against all odds: the “Lilien” (fleur-de-lis, SV Darmstadt 98) will play another season in the Bundesliga. However, the club says goodbye to one of his legends: Marco “Toni” Sailer (the man with the long beard next to Lambert Alff) leaves after this season.

E-MRS Spring Meeting in Lille

© Sharath Ulhas

More than one month before the German national soccer team comes to Lille, ATFT was there. Two PhD students – Sharath Ulhas and Stefan Vogel – represented the ATFT group at the EMRS (European Materials Research Society) spring meeting in Lille, France, which took place from May 2nd to 6th. Two talks and one poster on the topic Resistive Random Access Memories (RRAM) based on hafnium- and tantalum oxide were presented in Symposia D “Solid State Ionics: defect interactions and their influence on ionic and electronic transport”.

80th DPG spring meeting in Regensburg

March 2016 (Photo: Lambert Alff) – © Lambert Alff
March 2016 (Photo: Lambert Alff)

Following a long tradition, the Alff group participated with 10 contributions to the 80th annual DPG (Deutsche Physikalische Gesellschaft) spring meeting in the historic city of Regensburg. The group members gave talks in three sections: Thin Films, Dielectric Solids, and Magnetism. The topics ranged from resistive switching and novel permanent magnet materials to ordered 3d-5d double perovskites and highly conducting perovskite materials. The participating group members were from four different currents (Germany, India, Russia, and Iran). See you March 2017 in Dresden…

The transporter

February 2016 (Photo: Erwin Hildebrandt) – © Erwin Hildebrandt
February 2016 (Photo: Erwin Hildebrandt)

ATFT thin films get mobile by a novel vacuum suitcase which allows the transfer of films without breaking the vacuum. The custom designed system from Mantis Deposition GmbH allows the transfer of up to 6 flag-style sample holders at pressures of 10-9 mbar. It accommodates transfer heights from 1100 mm up to 1250 mm, and its pincer grip reaches 300 mm inside a connecting vacuum system from a DN KF40 port. A battery pack, a mobile turbo pumping station, 12 V charging capability, and the compact design facilitates the use of the system in narrow labs or a car trunk ensuring maximum mobility. A first sample exchange is planned with the group of Rainer Waser (FZ Jülich, RWTH Aachen).

A new aspect of the Verwey transition

In a recent paper by our group, M. Baghaie Yazdi et al. (Phys. Rev. B 93, 014439 (2016)), a so far neglected aspect of the famous Verwey transition in magnetite (Fe3O4, see image) has been unraveled by using X-ray absorption near edge spectroscopy (XANES, cooperation with the European Synchrotron Radiation Facility, ESRF) and polarized neutron reflectometry (collaboration with the Institute Laue-Langevin, ILL). The experiments indicate that a spin-state crossover from a high-spin state to a low- or intermediate-spin state likely is an essential ingredient of the Verwey transition puzzling the scientific community since 1939.

doi: 10.1103/PhysRevB.93.014439 (Image from: doi: 10.1088/1367-2630/15/10/103032)