Scientific Highlights from PSI's research departments
NUM (Condensed Matter Research with Neutrons and Muons)
New diluted ferromagnetic semiconductor with Curie temperature up to 180 K and isostructural to the ‘122’ iron-based superconductors
Diluted magnetic semiconductors have received much attention due to their potential applications for spintronics devices. A prototypical system (Ga,Mn)As has been widely studied since the 1990s. The simultaneous spin and charge doping via hetero-valent (Ga3+,Mn2+) substitution, however, resulted in severely limited solubility without availability of bulk specimens. Here we report the synthesis of a new diluted magnetic semi- conductor (Ba1-xKx)(Zn1-yMny)2As2, which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr2Si2 (122) structure. Holes are doped via (Ba2+,K1+) replacements, while spins via isovalent (Zn2+,Mn2+) substitutions. Bulk samples with x = 0.1-0.3 and y = 0.05-0.15 exhibit ferromagnetic order with TC up to 180 K, which is comparable to the highest TC for (Ga,Mn)As and significantly enhanced from TC up to 50 K of the ‘111’-based Li(Zn,Mn)As. Moreover, ferromagnetic (Ba,K)(Zn,Mn)2As2 shares the same 122 crystal structure with semiconducting BaZn2As2, antiferromagnetic BaMn2As2 and superconducting (Ba,K)Fe2As2, which makes them promising for the development of multilayer functional devices.
Facility: SμS
Reference: K. Zhao et al., Nature Communications 4, 1442 (2013)
Read full article: here
Reference: K. Zhao et al., Nature Communications 4, 1442 (2013)
Read full article: here
SYN (Synchrotron Radiation and Nanotechnology)
Atomic motions untangled
Schematic view of the femtosecond laser pump/x-ray probe
experiment performed at the FEMTO slicing source identifying the atomic motion coupled to the charge and orbital order in a manganite.
The pursuit of capturing motion in a movie bears an obvious fascination irrespective of the time scales involved. In the atomic and molecular world where the masses are so light and the distances small the relevant time scale shifts to the subpicosecond range and the motions become frantic especially for larger molecular systems. In the material class of strongly correlated electron materials the intricate balance of competing structural, magnetic and charge interactions complicates the picture when it comes down to disentangle the coupled processes. In order to advance the understanding of the underlying correlations in these materials current efforts focus on the interaction of the atomic, electronic, and magnetic subsystems on their relevant time scales. In particular, femtosecond x-ray or electron diffraction received considerable attention in the recent past because they enable direct access to the evolving atomic and electronic structure. Here, we study specific lattice modulations coupled to the melting of charge and orbital order in a manganite by means of femtosecond x-ray diffraction. By using a carefully chosen set of reflections combined with structure factor calculations we are able to identify the involved atomic motions.
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Original publication
Identification of coherent lattice modulations coupled to charge and orbital order in a manganite
A. Caviezel, S. O. Mariager, S. L. Johnson, E. Möhr-Vorobeva, S. W. Huang, G. Ingold, U. Staub, C. J. Milne, S.-W. Cheong and P. Beaud
PHYSICAL REVIEW B 87, 205104 (2013), DOI: 10.1103/PhysRevB.87.205104
Contact
Andrin Caviezel; Swiss Light SourcePaul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 5185, e-mail: andrin.caviezel@psi.ch
Dr. Paul Beaud; Swiss Light Source
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 4121, e-mail: paul.beaud@psi.ch
ENE (General Energy)
Radiation grafted membranes developed at PSI outlast state-of-the art commercial membranes in the fuel cell
Components for the polymer electrolyte fuel cell (PEFC) are required to show high performance and durability under application relevant conditions. Furthermore, for commercial viability the materials and processes for component fabrication need to be of los cost. The polymer electrolyte membrane developed at PSI on the basis of the radiation grafting technique has the potential of being produced in cost-effective manner. In recent years, we have collaborated with the Belenos Clean Power to further develop the membrane to commercial competitiveness. We managed, by careful analysis and optimization of the synthesis conditions, to close the performance gap to commercial membranes (Nafion). The durability of the PSI membranes was evaluated in a dynamic (accelerated) test to simulate an automotive cycle. Our membrane showed a durability much superior to that of the unreinforced commercial Nafion 212 membrane. It even outlasted the reinforced and chemically stabilized Nafion XL-100 membrane, a state-of-the-art material for challenging automotive applications. Beyond fuel cells, the radiation grafting technology can be adapted to design polymer electrolyte materials for other electrochemical applications of current and future interest, such as water electrolyzers, redox flow batteries and next-generation lithium batteries.
Presentation slides
BIO (Biology and Chemistry)
Effect of surface charge density on the affinity of oxide nanoparticles for the vapor–water interface
Research Department Biology and Chemistry (BIO), Surface Chemistry Group, Head Markus Ammann. Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.
Citation: M. A. Brown, N. Duyckaerts, A. B. Redondo, I. Jordan, F. Nolting, A. Kleibert, M. Ammann, H. J. Wörner, J. A. van Bokhoven and Z. Abbas, Langmuir 29, 5023 (2013)
Publication: http://dx.doi.org/10.1021/la4005054
Further publications: LCH Homepage
Publication: http://dx.doi.org/10.1021/la4005054
Further publications: LCH Homepage
GFA (Department Large Research Facilities)
ETH Zurich, IBM and Paul Scherrer Institut Researchers receive 2012 PRACE Award
PRACE Award
18.06.2012 HAMBURG: At the International Supercomputing Conference (ISC12) researchers from ETH Zurich, the renown science and technology university; IBM Research - Zurich and the Paul Scherrer Institute (PSI), Switzerland’s largest research centre for natural and engineering sciences, received the 2012 PRACE Award.
The PRACE Awards recognizes the best scientific paper in one of the following areas: a breakthrough in science achieved with high performance computing resources, algorithms or implementations that achieve significant improvements in scalability, or novel approaches to performance evaluation on massively parallel architectures.
Yves Ineichen, (ETH, IBM, PSI); Andreas Adelmann (PSI); Costas Bekas, Alessandro Curioni (IBM); and Peter Arbenz (ETH); received the award for their paper “A Fast and Scalable Low Dimensional Solver for Charged Particle Dynamics in Large Particle Accelerators.” ISC12
Citation for the award: “This paper demonstrates how HPC can be used in real time to tune the operation of particle accelerators, which are invaluable tools for research in the basic and applied sciences, in fields such as materials science, chemistry, the biosciences, particle physics, nuclear physics and medicine,” communicated by Prof. Richard Kenway, chairman of the PRACE Scientific Steering Committee.
About PRACE
The Partnership for Advanced Computing in Europe (PRACE) is an international nonprofit association with its seat in Brussels. The PRACE Research Infrastructure (RI) provides a persistent world-class High Performance Computing (HPC) service for scientists and researchers from academia and industry. The PRACE leadership systems form the apex of the performance pyramid and are well integrated into the European HPC ecosystem. PRACE receives funding from the EU's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° RI-261557.