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2015 Fall

Characterization of materials by experiments and computing


Nanoscale phase separations in spintronic materials, superconductors, and other systems

The symposium aims at bringing together researchers from both academia and large scale facilities (synchrotrons, centers for neutron scattering and for nuclear research,…) in order to present the latest advances in the synthesis and characterization of materials undergoing nanoscale phase separation, the mechanisms of phase separation, and the perspective functionality of these systems. Magnetically doped semiconductors, topological insulators, superconductors, magnetic oxides, but not only are in the focus.




The symposium aims at bringing together researchers from both academia and large scale facilities (synchrotrons, centers for neutron scattering and for nuclear research,…) in order to present the latest advances in: (i) the synthesis and characterization of materials undergoing nanoscale phase separation; (ii) the mechanisms of phase separation, and (iii) the perspective functionalities of these systems. Magnetically doped semiconductors, topological insulators,oxide and pnictidesuperconductors, magnetic oxides, but not only are in the focus. Particular attention will be paid to the fabrication and the structural, chemical, magnetic, optical, and transport characteristics of systems undergoing crystallographic, chemical, or electronic phase separations, which may give rise to the self-organized formation of nanostructures – e.g. dots and nanocolumns with predefined properties, controlled by the growth and co-doping protocols. In addition to fascinating physics, these materials show functionalities attractive for, e.g., flash memories, catalysis as well as various photonic, thermoelectric, and photovoltaic devices. Several tools with nanoscale resolution will be considered, including scanning probe, electron microscopy, synchrotron radiation, ion beam, neutron, and nuclear techniques as well as new families of nanoscale magnetometers. The recent progress in ab initio and multi-length scale simulation procedures assisting the fabrication procedures and the characterization methods as well suggesting new applications will be discussed.


Hot topics to be covered by the symposium


  • Similarities and differences between phase separation phenomena in various families of materials
  • New element-specific and spin-sensitive characterization methods
  • Application of phase-separated magnetic systems for spintronics, electronics, catalysis as well as for various photonic, thermoelectric, and photovoltaic devices


List of invited speakers:


  • Stephen Blundell, University of Oxford, UK, "High transition temperatures in molecular intercalates of FeSe"
  • Alberta Bonanni, Kepler University, Linz, Austria “Epitaxy and characterization of self‐organized modulated structures in (Al,Ga)N grown with Mn surfactant”
  • Lino Miguel da Costa Pereira, Leuven, Belgium, "Electron emission channeling with radioactive ions: lattice location of impurities in semiconductors and oxides"
  • Shuai Dong, Southeast University, Nanjing, China, “Surface and bulk phase separations in manganites”
  • Yaniv Gelbstein, Ben-Gurion University, Beer Sheva, Israel, “Enhancing thermoelectric efficiency by phase separation in alloys”
  • Zurab Guguchia, Paul Scherrer Institute, Villigen, Switzerland, "Coexistence of magnetism and superconductivity as seen by muon spin spectroscopy"
  • Matthieu Jamet, CEA, Grenoble, France, “Large scale facilities to study spinodal nanodecomposition in magnetically doped semiconductors”
  • Hiroshi Katayama‐Yoshida, Osaka University, Japan, “Spinodally decomposed system for catalysis and photovoltaics”
  • Shinji Kuroda, Tsukuba University, Japan, “Visualization of interplay between the formation of dots and nanocolumns in (Zn,Cr)Te and (Zn,Fe)Te”
  • Fumihiro Matsukura, Tohoku University, Sendai, Japan, “Effects of magnetic phase separation in (Ga,Mn)As”
  • Christopher Palmstrom, University of California in Santa Barbara, USA, “Self-assembly of rare-earth pnictide nanocrystals in III-V epilayers”
  • Dorota Anna Pawlak, Centre of New Technologies University of Warsaw and Institute of Electronic Materials Technology, Warsaw, Poland, "Bottom-up manufacturing methods for metamaterials and plasmonic materials"
  • Tomasz Story, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland, “Electric and thermoelectric properties of CdTe/PbTe epitaxial nanocomposite”
  • Maria Varela del Arco, Universidad Complutense de Madrid, Spain, “Atomic scale studies of chemical ordering in complex oxides”
  • Shengqiang Zhou, HZD, Rossendorf, Germany, “Application of ion beams to fabricate and characterize ferromagnetic semiconductors”


List of scientific committee members:


  • Antonio Bianconi, RICMASS, Roma, Italy
  • Francesco d'Acapito, ESRF, Grenoble, France
  • Bryan Gallagher, The University of Nottingham, UK
  • Haraldur Pall Gunnlaugsson, CERN, Geneva and Aarhus University, Denmark
  • Hideo Ohno, Tohoku University, Sendai, Japan
  • Roman Puźniak, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland


The symposium will be co-organized by the EU 7-th Framework Programme under the project REGPOT-CT-2013-316014(EAgLE).

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V and W Symposia Joint Session 1 : Ewa Jedryka; room: PhysAudyt
Authors : Alberta Bonanni
Affiliations : JKU Institute of Semiconductor and Solid State Physics

Resume : We summarize our recent work on the fabrication of III-nitrides doped with transition metals, with particular focus on the self-aggregation driven by fabrication parameters and co-doping [1] of functional magnetic nanocrystals [2-5], layered heterostructures [6,7] and magnetooptically active complexes [8,9]. An overview will be given on how we have unraveled and we can now control the correlation between the growth parameters and structural architecture, self-assembling of embedded crystalline nanostructures and phase separation that determine the magnetic, electric and optical response of the modulated systems. The work was supported by the European Research Council (ERC, Project #227690), by the Austrian Science Fundation (FWF, Projects #20065, #22477, #24471), by WRC ETI+ (Project NanoMat, P2IG.01.01.02-02-002/08 and the European Operational Programme Innovative Economy) and by the CAPACITIES project REGPOT-CT-2013-316014 (EAgLE). [1] A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010). [2] A. Bonanni et al., Phys. Rev. Lett. 101, 135502 (2008). [3] A. Navarro-Quezada et al., Phys. Rev. B 81, 205206 (2010). [4] A. Navarro-Quezada et al., Phys. Rev. B 84, 155321 (2011). [5] A. Grois et al., Nanotechnology 25, 395704 (2014). [6] T. Devillers et al., Cryst. Growth Des. 15, 587 (2015). [7] M. Rovezzi et al., arXiv1412.3932 [8] T. Devillers et al., Scientific Reports 2, 722 (2012). [9] T. Devillers et al., Appl. Phys. Lett. 103, 211909 (2013).

Authors : Matthieu JAMET
Affiliations : Univ. Grenoble Alpes, INAC-SP2M, F-38000 Grenoble, France. CEA, INAC-SP2M, F-38054 Grenoble, France.

Resume : The field of ferromagnetic semiconductors evolves very fast nowadays for their potential use in spintronic devices. Up to now, efforts have mainly focused on Diluted Magnetic Semiconductors but Curie temperatures in these materials still remain modest. One possible route to increase at least locally transition temperatures is to use spinodal nanodecomposition leading to the formation of transition metal-rich high-TC nanostructures [1]. We focus here on (Ge,Mn) considered as a model system for spinodal decomposition and compatible with Si-based microelectronics. (Ge,Mn) films grown on Ge substrates by molecular beam epitaxy at low temperature (<180°C) are free from secondary phase and contain self-assembled Mn-rich nanocolumns exhibiting high-TC [2]. In this talk, I will present a complete phase diagram of nanocolumns as a function of the substrate (Ge, GaAs) and growth temperature, Mn concentration and Sn co-doping focusing on their size, density, composition, morphology, crystalline structure and magnetic properties. For this purpose, we have used highly sensitive techniques at large scale facilities like synchrotron radiation based x-ray diffusion, diffraction and absorption, atom probe tomography, low energy muons spectroscopy and small angle neutron scattering. Only these techniques allowed us to probe in detail the physical properties at the nanoscale in the spinodally decomposed (Ge,Mn) system. [1] T. Dietl, K. Sato, T. Kukushima, A. Bonanni, M. Jamet, A. Barski, S. Kuroda, M. Tanaka, P. N. Hai, H. Katayama-Yoshida, arXiv: 1412.8062, accepted in Rev. Mod. Phys. (2015) [2] M. Jamet, A. Barski, T. Devillers, V. Poydenot, R. Dujardin, P. Bayle-Guillemaud, J. Rothman, E. Bellet-Amalric, A. Marty, J. Cibert, R. Mattana, S. Tatarenko, Nat. Mater. 5, 653 (2006).

V and W Symposia Joint Session 2 : Alberta Bonanni; room: PhysAudyt
Authors : L. Michez 1, F. D?Acapito 2, E. Prestat 3, M. Jamet 3, F. Boscherini 4, M. Petit 1, V. Le Thanh 1
Affiliations : 1 Aix-Marseille Universit? - CNRS CINaM-UMR, 13288 Marseille, France 2 ESRF, 38043 Grenoble, France 3 INAC/SP2M, CEA-Grenoble, Grenoble, France 4 University of Bologna, 40127 Bologna, Italy

Resume : Much attention has been recently devoted to Mn5Ge3 as this compound meets all the requirements for spin-polarized transport and injection into Ge. This material may therefore represent a new route to develop the beyond complementary metal-oxide-semiconductor technology. Its limited Curie temperature (TC~296K) greatly hinders its use for potential applications but can be enhanced up to 450K by incorporating a small amount of carbon. Theoretical calculations attribute this behavior to an enhancement of the Mn-Mn interactions mediated by C atoms placed in interstitial sites. In this work, we have extensively studied the structural and magnetic properties of Mn5Ge3Cx films grown on Ge(111) by molecular beam epitaxy as a function of C concentration. Besides the compressive strain induced by the incorporation of C, the latter modifies significantly the Mn5Ge3 magnetic properties. Whereas Tc increases from 296K to 450K, the magnetocrystalline anisotropy in C-doped samples is reduced by nearly a factor 10 as x is increased from 0 to 0.7. This effect is assigned to hybridization between Mn and C atoms whose position has been investigated via EXAFS and STEM experiments. The magnetic properties of carbon-doped Mn5Ge3Cx thin films can therefore be tuned by adjusting the amount of C. This is very promising for the realization of spintronics devices and in addition, the presence of C is essential for the thermal stability and the high performances of Mn5Ge3 thin films.

Authors : Irene Villa†, Anna Vedda†, Markus Niederberger‡, Alessandro Lauria‡*
Affiliations : †: Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy. ‡: Laboratory for Multifunctional Materials, Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland.

Resume : In this work we report the tunable optical features observed in undoped monoclinic HfO2 nanocrystals and their dependence on the structural properties of the material at the nanoscale. Transmission electron microscopy together with X-ray diffraction and surface area measurements were used to determine the fine structural modifications, in terms of crystal growth and coalescence of crystalline domains, occurring during a calcination process in the temperature range from 400 to 1000 °C. The fit of the broad optical emission into spectral components, together with time resolved photoluminescence, allowed us to identify the dual nature of the emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence (with decay time of few ns) overlaps with a slower emission (decay of several s) due to extrinsic Ti - impurity centres. Moreover, the evolution of intrinsic visible bands during the material transformation was monitored. The relationship between structural parameters uniquely occurring in nanosized materials and the optical properties was investigated and tentatively modelled. The blue emissions at 2.5 and 2.9 eV are clearly related to defects lying at grain boundaries, while an unprecedented emission at 2.1 eV enables, at relatively low calcination temperatures, the white luminescence of HfO2 under near-UV excitation.

Authors : D. A. Pawlak, M. Gajc, K. Sadecka, P. Osewski, K. Korzeb, S. Turczynski, K. Wysmułek, J. Sar
Affiliations : Institute of Electronic Materials Technology, Warsaw, Poland Centre of New Technologies, Warsaw University, Poland

Resume : Recent recognition that some materials (e.g. certain metals) have negative dielectric permittivities at frequencies below their plasma frequency, and therefore provide possibilities of fabricating hybrid materials of high impact for photonic applications, has caused rapid development of two new research areas: plasmonics and metamaterials. However, the fabrication of nanosized metallodielectric structures remains a challenge. Most current fabrication techniques arrange metal nanoelements on dielectric surfaces. The methods used are either time-consuming and costly (e.g. lithography), or restricted to the creation of two-dimensional structures at a limited production scale. One of the future ways of obtaining metamaterials or materials with unusual electromagnetic properties are the bottom-up manufacturing methods, which may enable manufacturing of two-dimensional and three-dimensional structures. Theoretical proposals for and experimental demonstrations of bottom-up approaches are scarce and exhibit drawbacks. Recently, we proposed the idea of utilizing directional solidification as a method for manufacturing metamaterials and plasmonic materials. We develop two methods: (i) method based on directionally-grown self-organized eutectic structures; and (ii) NanoParticles Direct Doping method (NPDD) based on directional solidification of dielectric matrices doped with various nanoparticles. In both of these methods we can easily use all available resonant phenomena to develop materials with unusual electromagnetic properties. Eutectics are simultaneously monolithic and multiphase materials forming self-organized micro/nanostructures, which enable: (i) the use of various component materials including oxides, semiconductors, metals, (ii) the generation of a gallery of geometrical motifs and (iii) control of the size of the structuring, often from the micro- to nanoregimes. On the other hand, the novel method of NanoParticles Direct Doping enables doping of dielectric matrices with various nanoparticles (varying chemical composition, size and shape) and with the possibility of co-doping with other chemical agents as eg. optically active rare earth ions or quantum dots. In both cases we apply one of the crystal growth methods - the micro-pulling down method - to create the material. This method has been originally developed for manufacturing of single crystalline fibres and than used for directional solidification of eutectics and finally for directional solidification of glasses. Utilizing described above methods we demonstrated (i) volumetric eutectic-based material with localized surface plasmon resonance at visible wavelengths; (ii) enhanced luminescence and up-conversion processes in the eutectic material exhibiting LSPR and co-doped with erbium ions; (iii) volumetric matrix-nanoparticles-based materials with plasmonic resonances at visible and IR wavelengths based on silver (Ag), antimony-tin-oxide (ATO) and titanium nitride nanoparticles (TiN); (iv) matrix-nanoparticles-based composite with enhanced photoluminescence at the telecommunication frequency of 1.5 µm; (v) material with subwavelength transmission at IR frequencies; (vi) material with anomalous refraction, evaluated by the beam deviation measurements; (vii) materials with enhanced Faraday effect; and (viii) materials for phonoanodes in photoelectrochemiacal cells for generation of hydrogen. All these results will be described. Our new approach based on utilizing the standard crystal growth methods combined with the bottom-up approach for manufacturing metamaterials and plasmonic materials leads to novel manufacturing solutions for applications in areas such as photonics, optoelectronics, photovoltaics and photoelectrochemistry.

V and W Symposia Joint Session 4 : Chris Palmstrom; room: PhysAudyt
Authors : Paolo M. Ossi
Affiliations : Dipartimento di Energia, Politecnico di Milano, via Ponzio 34-3, 20133 Milano

Resume : By nanosecond pulsed laser ablation in ambient gas nanoparticles (NPs) form and grow in the propagating laser-generated plasma plume. Such NPs mutually self-assemble on a substrate producing elaborated architectures with controllable morphology and increasing thickness. Besides laser wavelength, target to substrate distance, gas nature and pressure, at fixed laser energy density the energy per pulse and the spot size strongly affect the amount of ablated matter and thus plume energetics. At landing on the substrate NP size, energy and mobility affect film growth, morphology and physico-chemical properties. Ag and Au targets were ablated in Ar (10-100 Pa), changing the pulse number (500-30000), keeping constant target to substrate distance, incidence angle, laser wavelength and energy density. Films consisting of NP arrays were deposited on various substrates. The morphology ranged from isolated NPs to island structures, as observed by SEM and TEM. From fast imaging of the plume the plasma propagation regime and its initial velocity were determined. This data and the measured average ablated mass per pulse allow to model in-plume NP growth. Controlling growth parameters NP aggregation is finely tuned to obtain high-performance Surface Enhanced Raman Scattering (SERS) substrates. Good sensitivity and reproducibility of the SERS signal was proved for the anti-Parkinsonian drug apomorphine, in aqueous and in biological solutions and for the anti-epileptic drug carbamazepine.

Authors : P. Camarda, L. Vaccaro, F. Messina, M. Cannas
Affiliations : Department of Physics and Chemistry, University of Palermo, Italy

Resume : Pulsed laser ablation in liquid phase (PLAL) is a versatile method to synthesize high-purity nanomaterials such as ZnO nanoparticles (NPs), currently the subject of a large scientific interest stimulated by their promising technological applications. They are characterized by two emission bands both excited above the energy gap (3.4 eV): 1) exciton related at 3.3 eV; 2) defect related at 2.3 eV, commonly attributed to oxygen vacancies. Existing studies have used only ex-situ methods to characterize the endproducts of PLAL; these approaches only provide indirect information on the sequence of reactions ultimately yielding stable metal oxide NPs. In this work, we report online absorption (OA) and photoluminescence (PL) measurements carried out during and after PLAL of a Zn plate in H2O. Our experimental setup is original in that it uses the kinetics of OA and PL signals to follow in real time the dynamics leading to the formation of ZnO. We demonstrate that initially-produced Zn NPs are not "instantaneously" oxidized within the plasma plume, but rather as consequence of their reactions with H2O. In fact, ZnO NPs are formed by a sequence of two steps: an early, defect-free superficial oxidation of Zn NPs, followed by a second slower oxidation of the Zn core, finally producing sub-stoichiometric ZnO NPs rich of oxygen vacancies. This information can be used to control the defect concentration allowing the tuning of PL band of the ZnO NPs.

Authors : B. Kalska-Szostko*, U. Wykowska*, D. Satuła#
Affiliations : * Institute of Chemistry, University of Bialystok, Hurtowa 1, 15-399 Białystok, Poland #Department of Physics, University of Bialystok, Ciolkowskiego 1L, 15-245 Białystok, Poland

Resume : Nowadays, nanotechnology is a broad field of action of both science and everyday life. Continuously new materials are discovered with amazing physical and chemical properties. In case of nanoparticles, especially magnetic one are of special interest last time. It was find out that the properties strongly depend on the composition of core but also on the type of surface layer. For example, doping of iron oxide nanoparticles with different 3d metals, changes their magnetic properties significantly. When iron oxide nanoparticles are doped with Mn, Ni, or Co it enhances ferromagnetic properties usually observed. On the other hand when non-magnetic metals are used (Zn, Al) nanoparticles exhibit rather superparamagnetic behaviour at RT [1]. In this presentation we would like to show, how magnetite nanoparticles properties changes, while inorganic core is modified with different metals. Presented analysis of these structures include TEM, EDX, X-ray diffraction, and Mössbauer spectroscopy studies. [1] B. Kalska-Szostko, U. Wykowska, D. Satuła, Applied Surface Science 360 (2014) 7-15

Poster session 1 : Z. Guguchia, S. Zhou
Authors : R. Mantovan, H. P. Gunnlaugsson, K. Johnston, H. Masenda, T. E. Mølholt, D. Naidoo, M. Ncube, S. Shayestehaminzadeh, K. Bharuth-Ram, M. Fanciulli, H. P. Gislason, G. Langouche, S. Ólafsson, L. M. C. Pereira, U. Wahl, P. Torelli and G. Weyer
Affiliations : R. Mantovan, M. Fanciulli, Laboratorio MDM, IMM-CNR, I-20864 Agrate Brianza, MB, Italy; H. P. Gunnlaugsson, G. Langouche, L. M. C. Pereira KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium; H. P. Gunnlaugsson, G. Weyer, Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark; K. Johnston, Physics Department, ISOLDE/CERN, 1211 Geneva 23 , Switzerland; H. Masenda, D. Naidoo, M. Ncube, School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa; T. E. Mølholt, S. Shayestehaminzadeh, H. P. Gislason, S. Ólafsson, Science Institute, University of Iceland, IS-107 Reykjavík, Iceland; K. Bharuth-Ram, School of Physics, Durban University of Technology, Durban 4000, South Africa, iThemba LABS, Somerset West 7129, South Africa; M. Fanciulli, Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano, Italy; U. Wahl, Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2686–953 Sacavém, Portugal; P. Torelli, Laboratorio TASC, IOM-CNR, I-34149 Trieste, Italy.

Resume : In the search for dilute magnetic semiconductors and oxides, typical (and critical) issues concern the potential presence of extrinsic contamination and/or unwanted precipitates of 3d-atoms being the source of ferromagnetism, when investigated by volume-integrating techniques. In the recent years, contradictory results have been reported in very similar systems, under apparently comparable preparation conditions. In this contribution, the magnetic properties at the atomic level of Fe atoms incorporated in ZnO, in a concentration range of more than five orders of magnitude from 1E-5 to 2.2 at.% are probed using emission 57Fe Mössbauer spectroscopy on implanted 57Mn and 57Co produced at ISOLDE/CERN. In the ultra-dilute regime (1E-5 at. %), the system shows isolated paramagnetic Fe3+ ions with a spin-lattice type of relaxation. At higher concentrations (between 0.02 and 0.2 at. %) a transition to spin-spin type of relaxation between neighboring Fe3+ is observed, without any signature of magnetic ordering up to 2.2 at.% [1]. Our results suggest that the absence of room temperature magnetic ordering in wide band gap and truly diluted semiconductors could be a general conclusion, attributable to the absence of efficient mechanisms to mediate long-range interactions. [1] Mantovan et al., Advanced Electronic Materials 1, 1400039 (2015).

W.W I.1
Authors : T.A.L. Lima1, U. Wahl2, J.G. Correia2, V. Augustyns1, F. Kremer5, K. W. Edmonds3, B. L. Gallagher3, and R. P. Campion3, J.P. Araújo4, M.C. Ridgway5, K. Temst1, A. Vantomme1, L.M.C. Pereira1
Affiliations : 1) KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium; 2) Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2686-953, Sacavém, Portugal; 3) School of Physics and Astronomy, University of Notthingham, Notthingham, NG7 2RD, United Kingdom; 4) IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Universidade do Porto, 4169-007 Porto, Portugal; 5) Department of Electronic Materials Engineering, RSPE, Australian National University, Canberra ACT 2601, Australia.

Resume : Mn-doped GaAs, a model dilute magnetic semiconductor (DMS), is also the ideal example of how the electric and magnetic behavior of DMS is strongly influenced by the lattice sites occupied by the magnetic dopants. We present emission channeling experiments on the lattice location of radioactive 56Mn in ferromagnetic (Ga,Mn)As thin films (1-6% Mn). We show that interstitial Mn occupies the tetrahedral site with As nearest neighbors both before and after thermal annealing at 200°C, whereas the occupancy of the tetrahedral site with Ga nearest neighbors (T-Ga) is negligible [1]. Furthermore, we show that the thermal stability of both interstitial and substitutional Mn, with respect to diffusion and segregation, significantly decreases with increasing Mn concentration. These findings shed new light on the mechanism of Mn self-compensation in (Ga,Mn)As by: (i) demonstrating that the strong dependence of the Curie temperature on annealing temperature in the vicinity of 200°C results from the competition between interstitial Mn diffusion and substitutional Mn segregation; (ii) supporting the notion that the formation of interstitial Mn during growth is a non-equilibrium process. [1] T.A.L. Lima et al., Appl. Phys. Lett. 106, 012406 (2015).

W.W I.2
Authors : Michał Musiał 1#, Mariusz Drygaś 1, Jerzy F. Janik 1, Jacek Gosk 2, Andrzej Twardowski 3
Affiliations : 1 AGH University of Science and Technology, Faculty of Energy and Fuels; Al. Mickiewicza 30, 30-059 Kraków, Poland; #graduate student 2 Warsaw University of Technology, Faculty of Physics; ul. Koszykowa 75, 00-662 Warszawa, Poland 3 University of Warsaw, Faculty of Physics; ul. Hoża 69, 00-681 Warszawa, Poland

Resume : The starting nanopowders of gallium nitride GaN were made via nitriding pyrolysis of gallium imide. The range of pyrolysis temperatures, 600-975 C, resulted in nanopowders with diverse properties including polytype/particle size features and BET specific surface areas. They were treated with a hexane solution of manganese bis(trimethylsilyl)amide followed by removal of volatiles. Finally, the resulting solids were pyrolyzed under ammonia at 200 C to promote nitridation reactions of the adsorbed Mn-precursor. The substrate powders and resulting products were investigated by XRD, SEM, XPS, UV-vis, FT-IR, and BET specific surface area and He density determinations. Also, magnetic properties of the Mn-treated products were studied with SQUID. The investigation confirmed binding of Mn-centers on the surfaces of GaN nanoparticles/agglomerates. The amount of directly surface-attached species was a function of the BET surface area/helium density. The magnetic study was consistent with the coexistence of a paramagnetic phase typical for GaMnN substitutional structures and an antiferromagnetic phase due to residual/excess Mn by-products. Acknowledgement. Study was funded by the Polish National Science Centre NCN, Grant No. 2011/01/B/ST5/06592.

W.W I.4
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Authors : Dymtro Dedovets1,2, Satyabrata Si1, Emilie Pouget2, Jiaji Cheng2 Sabrina Habtoun3, Said Houmadi3, Christian Bergaud3, Reiko Oda2, Marie-H?l?ne Delville1
Affiliations : 1 Institut de Chimie de la Matiere Condensee de Bordeaux, CNRS UPR 9048, Universite of Bordeaux 87 Avenue du Dr Schweitzer F-33608 Pessac Cedex FRANCE (*email: 2 CBMN, All?e Geoffroy Saint Hilaire, B?t B14, 33600 Pessac

Resume : In the field of emerging nanoscale materials with switchable properties chiral structures like helices or twisted ribbons are of great interest because of their intrinsic optical and mechanical properties. In this contribution, we present a study about the mechanical properties of SiO2 and SiO2@MxOy nanotubes and helical nanosprings synthesized by an original and simple technique from organic nanotubes through inorganic transcription. These nano-objects have potential applications in NEMS, ranging from physical sensing and signal processing to ultra-low power radio frequency signal generation, thanks to their striking features. NEMS have been generally based on 1D nano-objects, such as carbon nanotubes or silicon nanowires. However, the use of 3D nanostructures such as nanohelices would allow a significant improvement the electromechanical performances of functional nanodevices, due to their specific properties. The originality of our synthesis method consists in the possibility to obtain 3D nanostructures with specific morphology and properties. Hybrid nano-helices are synthesized using amphiphilic organic chiral self-assemblies forming very well defined helix or ribbons structures and exploits them as templates for inorganic nanomaterial formation[1]. Their bio-inspired mineralization creates silica nano-helices with very well controlled morphologies usable in functional nanodevices such as sensors, actuators and resonators. To the best of our knowledge, nothing has been

Authors : L.M.C. Pereira1, U. Wahl2, J.G. Correia2, V. Augustyns1, T.A.L. Lima1, K. W. Edmonds3, B. L. Gallagher3, R. P. Campion3, A. Bonanni4, F. Kremer5, M.C. Ridgway5, J.P. Araújo6, K. Temst1, A. Vantomme1
Affiliations : 1) KU Leuven, Instituut voor Kern- en Stralingsfysica, 3001 Leuven, Belgium; 2) Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2686-953, Sacavém, Portugal; 3) School of Physics and Astronomy, University of Notthingham, Notthingham, NG7 2RD, United Kingdom; 4) Institut fur Halbleiter-und-Festkörperphysik, Johannes Kepler University, 4040 Linz, Austria; 5) Department of Electronic Materials Engineering, RSPE, Australian National University, Canberra ACT 2601, Australia; 6) IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Universidade do Porto, 4169-007 Porto, Portugal.

Resume : The magnetic and electric properties of dopants in semiconductors strongly depend on the lattice sites which they occupy. While the majority site can often be predicted based on chemical similarities with the host elements and is usually simple to confirm experimentally, minority sites are far more difficult to predict, detect and identify. Dilute magnetic semiconductors (DMS) are perfect examples of such complex dopant lattice location underlying complex magnetic and electric phenomena. We overview recent emission channeling studies (at ISOLDE-CERN) on the lattice location of transition metals in DMS (Mn in GaAs [1]; Mn/Fe/Co/Ni in GaN and ZnO [2]) from the highly dilute (< 0.05%) to the typical DMS (several %) regime. We discuss in particular (1) the competition between substitutional and interstitial occupancy in Mn-doped GaAs, and (2) the puzzling anion substitution observed for some transition metals in ZnO and GaN. We also present ongoing work beyond DMS, in the wider context of magnetic doping of insulators (e.g. topological insulators and artificial multiferroics), involving channeling techniques and others (e.g. synchrotron-based). [1] Appl. Phys. Lett. 106, 012406 (2015); Physical Review B 86, 125206 (2012); Appl. Phys. Lett. 98, 201905 (2011). [2] Nucl. Instr. Meth. Phys. Res. 332, 143 (2014); J. Phys.: Cond. Matter 25, 416001 (2013); Appl. Phys. Lett. 103, 091905 (2013); Phys. Rev. B 86, 195202 (2012); Phys. Rev. B 84, 125204 (2011).

Authors : J. Sadowski (1,2), S. Kret (1), A. Siusys (1), T. Wojciechowski (1), R. Mathieu (3), M. Sawicki (1)
Affiliations : (1) Institute of Physics, Polish Academy of Sciences, Warszawa, Poland; (2) MAX-IV laboratory, Lund University, Sweden; (3) Department of Engineering Sciences, Uppsala University, Sweden

Resume : Decomposition of (Ga,Mn)As - a canonical dilute ferromagnetic semiconductor, has been studied since the very beginning of the research activity devoted to this material [1]. (Ga,Mn)As is a metastable compound, which can only be obtained by highly nonequilibrium growth methods like molecular beam epitaxy, hence it is fairly easy to convert it to a phase segregated material with MnAs nanocrystals embedded in GaAs matrix, applying high temperature post-growth annealing. This hybrid system is interesting because of room-temperature ferromagnetic properties of MnAs; thus it is suitable for fabrication of prototypical spintronic devices taking advantage of integration of metallic, ferromagnetic MnAs nano-magnets with the semiconducting GaAs host. In contrast to previous reports devoted to MnAs nano-inclusions embedded in GaAs layers, here we investigate quasi-one-dimensional case of MnAs nanocrystals incorporated into thin shells of GaAs nanowires. We provide evidences that the preferred location for MnAs segregation is correlated with the stacking fault (SF) defects of GaAs NW cores. This enables an adjustment of the distribution of MnAs nanocrystals along the NW axes; since the distribution of SF defects can be controlled by the NW growth conditions [2]. This work has been supported by the project 2014/13/B/ST3/04489 financed through the Polish National Science Centre. [1] J. De Boeck, et. al., Appl. Phys. Lett. 68, 2744 (1996). [2] T. Burgess, et. al. ACS Nano 7, 8105 (2013).

Session 7 : Maciej Sawicki; room: Math101
Authors : Shinji Kuroda
Affiliations : Institute of Materials Science, University of Tsukuba

Resume : In the search of novel magnetic semiconductors, an attempt to incorporate magnetic element in a high content often results in a phase separation into regions with high and low contents of magnetic elements. There are two types of phase separation; the aggregation of magnetic elements with keeping crystal structure coherent to the host semiconductor (chemical phase separation) and the precipitation of nanocrystals of an extrinsic phase (structural phase separation)[1]. In this presentation, we will show our recent experiments on the phase separation and its correlation with magnetic properties in II-VI magnetic semiconductors (Zn,Cr)Te and (Zn,Fe)Te, which were grown by molecular beam epitaxy. In (Zn,Cr)Te, it is found that the co-doping of iodine as a donor impurity enhances the phase separation[2]. With the increase of Cr content or the growth temperature, the type of phase separation changes from chemical to structural phase separation[3]. In (Zn,Fe)Te, the growth with a surplus supply of Zn flux over Te flux induces the formation of Fe-rich columnar regions, which appear to be structurally coherent to the host crystal[4]. Details will be presented at the conference. [1] T. Dietl et al., Rev. Mod. Phys., in press. [2] S. Kuroda et al., Nat. Mater. 6, 440 (2007). [3] H. Kobayashi et al., Physica B 407, 2947 (2012). [4] S. Ishitsuka, Phys. Stat. Sol. (c) 11, 1312 (2014).

Authors : V.D. Popovych*, P.Sagan, M.Bester, B. Cieniek, I. Stefaniuk, M. Kuzma
Affiliations : Faculty of Mathematics and Natural Sciences, Department of Experimental Physics University of Rzeszow, Pigonia 1, 35-959 Rzeszow, Poland. *Department of Fundamental Technologies, Ivan Franko Drogobych State Pedagogical University, 24 Ivan Franko str., 82100, Drogobych, Ukraine

Resume : Cr-doped CdTe crystals were theoretically predicted to be DMS with high Curie temperature due to superexchange spin interaction between nearest-neighbor Cr2 ions substituted cadmium atoms in the host lattice [1]. However, it was also reported that room-temperature ferromagnetism in Cr-based AIIBVI compounds could possibly be associated with precipitation of dopant-related secondary phases [2] caused by poore chromium solubility in the host matrix. In the present work we investigated CdTe:Cr single crystals grown by physical vapour transport method from pre-synthesized (Cd,Cr)Te alloys with 2.5 and 5 at.% of chromium nominal content. Arranged sets of extrinsic phase precipitates were revealed by means of SEM patterning of the (110)- and (111)-oriented surfaces of the crystals, both in the form of nm-sized near-isometric particles and platelets with sub-μm thickness. Using EDX profiling, HAADF elemental mapping and HRTEM measurements coupled with FFT images analysis, it was determined that the observed defects are composed of Cr-Te intermetallic compounds coherent with {111} and {100} planes of the zinc-blende structure of CdTe environment. Magnetic properties of the grown crystals were studied by means of EPR data obtained using X-band Bruker spectrometer (9.43 GHz). The angular dependence of spectrum showes two sets of fine components originated from substitution Cr2 ions in the CdTe host matrix and from precipitated CrTe-related phases. [1] J. Blinowski, P. Kacman, J.A. Majewski, J. Cryst. Growth. 159 (1996) 972. [2] Sreenivasan, M.G., Teo, K.L.; Cheng, X.Z.; Jalil, M.B.A.; Liew, T.; Chong, T.C.; Du, A.Y.; Chan, T.K.; Osipowicz, T.,Structural, magnetic, and transport investigations of CrTe clustering effect in (Zn,Cr)Te system, Journal of Applied Physics, v 102, n 5, 2007, p 053702

Authors : Ye Yuan, Hua Cai, Manfred Helm, Shengqiang Zhou
Affiliations : Helmholtz-Zentrum Dresden-Rossendorf

Resume : Dilute magnetic semiconductors (DMSs) attracted great interests in the last several decades because of their potential for spintronic device [1]. III-V compounds especially GaAs based DMS has recently emerged as the most popular material for this new technology. However, that the low mobility of holes in p-type DMS limits the potential application in semiconductor spintronic devices. Therefore, the searching for n-type DMS is of interest. The doping of Fe in InAs is attracting research attentions due to the possibility to fabricate n-type diluted magnetic semiconductors [2, 3]. However, the low solubility of Fe in InAs is the most difficulty to achieve InFeAs DMS. In this work, we obtain Fe doped InAs layers by ion implantation and pulsed laser annealing. This approach has shown success for preparing other III-V based DMSs [4, 5]. The formed InFeAs layers are proved to be epitaxial-like on InAs substrates. The prepared InFeAs layers reveal similar magnetic properties independent of their conductivity types. While the samples are lacking of charactersistics of DMS, they appear to be superparamagnetic behavior, revealing such as time-dependent magnetiszation measurements reveal aging and memory effects. 1. T. Dietl et al., Science 287, 1019-1022 (2000) 2. M. Kobayashi et al., Appl. Phys. Lett., 105, 032403(2014) 3. P. Nam Hai et al., Appl. Phys. Lett., 101, 182403 (2012) 4. D. B?rger et al., Phys. Rev. B, 81, 115202 (2010) 5. M. Khalid et al., Phys. Rev. B, 89, 121301(R

Authors : Bao-Hsien Wu, Wei-Ting Liu, Lih-Juann Chen
Affiliations : National Tsing Hua University

Resume : Nowadays, the energy and environmental issues have become increasingly important. To convert sustainable energy into chemical fuels, the photocatalytic hydrogen production by semiconductor materials have received a great deal of attention. On the other hand, in order to develop efficient photocatalysts, two important factors must be taken into consideration: shifting the light absorption range to visible light and increasing the photogenerated charge carriers. Recent studies have shown that by introducing plasmonic metal, the photocatalytic efficiency of semiconductor can be improved via plasmon-enhanced light absorption. In the present work, we have successfully synthesized hexagonal close-packed core-shell Au/TiO2 hybrid nanocrystal arrays by a facile process, which includes arrangement of hexagonal close-packed metal nanocrystal arrays and deposition of TiO2 by atomic layer deposition (ALD). The localized surface plasmon resonance (LSPR) properties of the hybrid nanocrystal arrays have been investigated, which is consistent with the simulation based on Mie theory. Through tuning the thickness of TiO2 shell or changing the size of Au core, the LSPR wavelength can be systematically controlled. The hybrid Au/TiO2 nanocrystal arrays were then employed as photocatalysts in aqueous methanol solution. In comparison with bare TiO2 thin film, the hybrid Au/TiO2 nanocrystal arrays indeed exhibited notable increases in the amount of hydrogen from methanol solution splitting under both ultra-violet and visible light, which is attributed to the plasmon-enhanced light absorption. Based on finite difference time domain (FDTD) simulation, the electric field in TiO2 has been enhanced by LSPR, hence increased the generation of electron and hole pairs.

Authors : E.D. Glowacki,1 M. Sytnyk,2 Z. Bozkurt,2 N. S. Sariciftci,1 W. Heiss2
Affiliations : 1. Physical Chemistry, Johannes Kepler University, Linz, Austria 2. Institute of Materials for Electronics and Energy Technology (i-MEET) Friedrich- Alexander-University Erlangen-Nuremberg, Erlangen, Germany; and Energie Campus Nurnberg (EnCN), Nurnberg, Germany

Resume : Here we describe processes to transform archetypical commercial organic pigments into colloidal micro and nanocrystals suitable for solution processing of high-quality transistors, biosensors, and photosensors. Our methodology relies on ligand-mediated syntheses, transforming industrial colored pigment powders into stable colloidal solutions of semiconductor nanocrystals, highly suitable for electronic device developments. Tuning of process conditions can yield nanocrystals with zero, one-, two- and three-dimensional shapes, exhibiting a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near infrared. The utility of such colloidal nanocrystals is demonstrated in photodetectors with responsivities up to 1 A/W, and humidity sensors operating over a dynamic range of 7 orders of magnitude and ~0.1s response. Both devices are fabricated by paint brushing or drop casting of these nanocrystals on paper substrates and outperform devices prepared from the same starting materials by vacuum deposition by several orders of magnitude. Properties can be further contolled through the use of biofunctional ligands such as riboflavin, flavin mononucleotide, and phosphonic acids. We demonstrate dedicated functionality leading to selective bioresponse. Importantly, these crystals are found to exhibit excellent operational stability in both air and various aqueous ionic environments. The semiconducting nanocrystals described here offer a cheap and nontoxic alternative to inorganic nanocrystals, as well as a new paradigm for obtaining organic semiconductor materials from low-cost and nontoxic commercial colorants.

Authors : Seung-Myung Yoo, Ki-Bum Lee, and Chunghee Nam
Affiliations : Department of Photonics and sensors, Hannam Unversity

Resume : Hydrothermal synthesis is one of liquid-phase synthesis methods with water or an aqueous solution under high pressure and high temperature. This paper reports the growth of magnetic Fe3O4 particles from iron powder (spherical, <10 micron) through an alkaline hydrothermal process with different KOH Molar concentration at the same hydrothermal time. In addition, the phase and shape variations with the addition of Potassium hydroxide (KOH), Ethylene diamine (EDA), or KOH and EDA were investigated and compared. Morphologies of the synthesized magnetic particles were characterized by X-ray diffraction(XRD, 2θ= 20°~80°) with Cu-kα radiation and field emission scanning electron microscopy(FE-SEM). Structure characterization showed that the phase structure of the particles evolved from Iron powder to Fe3O4 with increasing concentration of KOH and EDA. We observed an interesting role of KOH on the formation of magnetite octahedron. Finally, the magnetite properties of Iron oxide were studied by using a vibrating sample magnetometer (VSM), showing that Fe3O4 can be simply fabricated by hydrothermal methods.

W.W II.2
Authors : G.Gorokh(1), N.Kalanda(2)
Affiliations : (1)Belarusian State University of Informatics and Radioelectronics, 6 P.Brovka Str., 220013 Minsk, Belarus (2)Scientific-Practical Materials Research Centre of NAS of Belarus, 19 P. Brovka Str., 220072 Minsk, Belarus

Resume : Low-dimensional composition structures, having the spin-polarized electric charge transfer through the dielectric boundaries were obtained on the base of Sr2FeMoO6-d (SFMO) compounds films in Al2O3 porous templates. The advantage of SFMO is caused by its high Curie temperature (~ 400 К) and almost 100% degree of the spin polarization. After the deposition SFMO films had a single-phase composition, but low values of their magnetization have shown the absence of the superstructural ordering of Fe3+ and Mo5+ cations, due to the presence of the antistructural defects of FeMo and MoFe type. This is caused by the appearance of the antiferromagnetic domains, because of the destruction of - Fe3+ - Mo5+- Fe3+- chains. An optimization of the structurally-perfect SFMO films synthesis in the Al2O3 template has been achieved by the ion assistance method, with a bombardment of the film surfaces by Аr+ ions. Investigation of these films microstructure has confirmed their uniformity and homogeneity, due to the formation of active centers in the form of radiation defects on the surface of the samples surface as a result of the ion assistance. This leads to the fine-grained structure of the films. Results of the measurements of the field dependence of magnetization show a decrease of the SFMO films coercitive force after the ion assistance and an increase of the electrons spin polarization.

W.W II.3
Authors : Henryk Puszkarski and Piotr Tomczak
Affiliations : Faculty of Physics, Adam Mickiewicz University

Resume : Spin-wave resonance (SWR) is a newly emerged method for studying surface spinwave modes (SSWMs) in (Ga,Mn)As thin films. The existence of SSWMs in (Ga,Mn)As thin films was recently reported by Liu et al. [1], which observed SSWMs in the in-plane configuration (with variable azimuth angle ϕ between the in-plane magnetization of the film and the surface [100] crystal axis) – SSWMs are observed in the azimuth angle range between two in-plane critical angles ϕc1 and ϕc2. On the basis of our recent theoretical SWR studies [2, 3] we show here that the cubic surface anisotropy is an essential factor determining the existence conditions of SSWMs. The following conclusion is drawn from our considerations: in a (Ga,Mn)As thin film conditions favorable for the occurrence of surface spin-wave modes in the in-plane configuration are fulfilled first of all for those azimuth orientations of the magnetization of the sample that lie around the hard axes of cubic magnetic anisotropy. This implies that a hard cubic anisotropy axis plays the role of an easy axis for the spin pinning; we can refer to it as an easy surface pinning axis (an axis from which spins diverge easily). This study is a part of a project financed by Narodowe Centrum Nauki, Grant no. DEC-2013/08/M/ST3/00967. References [1] X. Liu, Y.-Y. Zhou, and J. K. Furdyna, Phys. Rev. B 75, 195220 (2007). [2] H. Puszkarski and P. Tomczak, Sci. Rep. 4, 6135 (2014). [3] H. Puszkarski and P. Tomczak, Phys. Rev. B 91, 195437 (2015).

W.W II.4
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Authors : Marco Truccato, Angelo Agostino, Lorenzo Mino, Elisa Borfecchia, Eleonora Cara, Alessandro Pagliero, Lise Pascale, Lorenza Operti, Emanuele Enrico, Natascia De Leo, Matteo Fretto, Gema Martinez-Criado, Carlo Lamberti
Affiliations : Marco Truccato, Eleonora Cara, Alessandro Pagliero, Department of Physics, Interdepartmental Centre NIS, University of Torino, via Giuria 1, I-10125 Torino, Italy; Angelo Agostino, Lorenzo Mino, Elisa Borfecchia, Lise Pascale, Lorenza Operti, Department of Chemistry, University of Torino, via Giuria 7, I-10125 Torino, Italy; Emanuele Enrico, Natascia De Leo, Matteo Fretto, INRIM, National Institute of Metrological Research, Strada delle Cacce 91, I-10135 Torino, Italy; Gema Martinez-Criado,Experiments Division, European Synchrotron Radiation Facility, 6, rue Jules Horowitz, B.P. 220, F-38043 Grenoble Cedex, France; Carlo Lamberti, Southern Federal University, Zorge Street 5, 344090 Rostov-on-Don, Russia

Resume : We report on the fabrication of a proof-of-concept device by means of a novel direct-writing, X-ray nanolithography approach, which represents a natural extension of our recent studies on the influence of synchrotron radiation on the oxygen content of the Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide [1]. Selected areas of Bi-2212 microcrystals have been exposed to a 17.7 keV beam with a spot size of about 57x45 nm2 and a flux of 1-5x1011 ph/s. The irradiated regions have resulted in trenches able to force the current along the c-axis, therefore patterning a stack of intrinsic Josephson junctions. Indeed, the I-V curves clearly show the typical Josephson pattern, confirming that the delivered radiation dose was enough to locally turn the material into a non-superconducting state. Morphological analysis shows that no material has been removed from the trenched regions, but some local volume expansion can be observed. X-ray nanodiffraction frames collected at the irradiated areas show the presence of Bi-2212 peaks along with a Bi2O3 polycrystalline phase that does not appear in the non-irradiated regions. Our results represent a novel patterning method that in principle could be extended to several oxide materials. Possible advantages of this method can be represented by improved mechanical stability, absence of chemical contamination and of vacuum/oxide interfaces, and in potential higher steepness of the patterned structures. [1] A.Pagliero et al. Nano Lett. 2014, 14, 1583

Authors : R. Puzniak1, V. Markovich2, I. Fita1, A. Wisniewski1
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, 02-668 Warsaw, Poland, 2Department of Physics, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel

Resume : Charge-ordered (CO) state and antiferromagnetism are very stable in bulk samples of half-doped and electron-doped perovskite manganites but they become significantly suppressed and accompanied by an enhanced ferromagnetism upon reduction of the grain size. Magnetic studies of nanoparticles (NPs) with reduced grain size are exciting since properties of the particle core differ significantly from those of the shell and core-shell interaction leads to unexpected effects. With decreasing particle size from 60 to 15 nm for Sm0.43Ca0.57MnO3 and from 80 to 20 nm for Sm0.27Ca0.73MnO3, the relative volume of the ferromagnetic (FM) phase increases monotonously, while the CO phase progressively weakens and disappears completely in Sm0.43Ca0.57MnO3 NPs of average 15 nm particle size. Field cooled magnetization hysteresis loops of Sm0.1Ca0.9MnO3 NPs exhibit horizontal and vertical shifts, relatively small in 60 nm and much larger in 25 nm particles, due to size-dependent exchange bias effect. The exchange bias field and the coercive field depend in a non-monotonic way on cooling magnetic field. We have ascribed the magnetic behavior of the nanoparticles to a core-shell scenario with phase separated core containing FM clusters embedded in an antiferromagnetic (AFM) matrix and partially disordered AFM or paramagnetic shell. The suppression of the FM phase in the core with decreasing particle size may account for the enhancement of the exchange bias effect seen in smaller particles.

Authors : I. Fina1, J. Clarkson2, C. Frontera3, K. Cordero1, S. Wizotsky4, F. Sanchez3, X. Marti5, G. Catalan1, J. Fontcuberta3, R. Ramesh2,6
Affiliations : 1 ICN2-Institut Català de Nanociència i Nanotecnologia, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain. 2 Department of Materials Science and Engineering and Department of Physics, University of California, 94720 Berkeley, California, USA 3 Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus UAB, Bellaterra E-08193, Spain 4 Max Planck Institute of Microstructure Physics, Weinberg 2, Halle D-06120, Germany 5 Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 162 53 Praha 6, Czech Republic 6 Materials Science Division, Lawrence Berkeley National Laboratory, 94720 Berkeley,

Resume : Data encryption is the cornerstone of today's trust in the telecommunications arena. At present, complex algorithms are implemented in adjacent integrated circuits, which translate between actual and garbled information. Beyond requiring dedicated circuitry, this paradigm allows replicating the translating machine / algorithms. In this present, we present a magnetic media which spontaneously encrypts its contents at a mixed-phase boundary between ferromagnetic and antiferromagnetic phases. We show how data retrieval and editing is performed at the ferromagnetic phase, following the inspiration by Heat-Assisted Magnetic Memories, which are already coping its own niche in the non-volatile memory shelf. A detailed study allows us to conclude that the presence of coexisting phases at room temperature is an essential requirement for the observed memory effects. The ample availability of materials with mixed-phase phenomena close to room temperature anticipates that the findings reported here are not, by any theoretical perspective, limited to the specific material employed here, namely FeRh.

Authors : Agnieszka Jamroz, Lukasz Gladczuk, Jacek A. Majewski
Affiliations : Faculty of Physics, University of Warsaw, ul. L. Pasteura 5, 02-093 Warszawa, Poland

Resume : Group IV elements (C, Si, Ge, Sn), their binary alloys, and the alloys doped with group III and V elements can be stabilized in the form of honeycomb two-dimensional lattices. We employ first principles calculations in the framework of the density functional theory augmented by Monte Carlo calculations (within NVT ensemble and with valence force field Tersoff like potentials) to study the cohesive and electronic properties of ordered and disordered binary alloys of the whole plethora of the honeycomb monoatomic systems consisting of group IV atoms. For the ordered alloys, we determine phase diagrams, morphology of the structures leading to local total energy minima and possibility of transitions between structures under the external stress. For disordered AxB1-x alloys with x up to 50%, we determine the equilibrium structure and quantify the degree of the short- and long-range order in the alloys with the Warren-Cowley and Brag-Williams parameters, respectively. The ordered Si-C, Ge-C, and Sn-C alloys acquire highly energetically preferable low buckled equilibrium phase and have fairly large energy gap (roughly 2 eV). The disordered alloys with carbon are not random but exhibit rather large degree of short-range order. Further, we perform comparative study of the n and p-type doped systems on the basis of graphene and silicene, i.e., BC, NC, BNC, AlSi, PSi, AlPSi, to find out that these structures exhibit typically large degree of the short order.

Authors : Zurab Guguchia
Affiliations : Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut

Resume : In this talk the results of the interplay between magnetism and superconductivity, obtained for the cuprate system La2-xBaxCuO4 (x = 1/8) and for the binary helimagnet CrAs, will be presented. Magnetism and superconductivity was studied in the static stripe phase of LBCO-1/8 by means of magnetization and muon-spin rotation (µSR) experiments as a function of pressure up to p = 2.2 GPa [1]. With increasing pressure the spin order temperature and the size of the ordered moment are not changing significantly. However, application of hydrostatic pressure leads to a remarkable decrease of the magnetic volume fraction Vm(0). Simultaneously, an increase of the SC volume fraction Vsc(0) occurs. Furthermore, it was found that Vm(0) and Vsc(0) at all p are linearly correlated: Vm(0) + Vsc(0) = 1. This is an important new result, indicating that the magnetic fraction in the sample is directly converted to the SC fraction with increasing pressure. The present results provide evidence that static stripe order and bulk superconductivity occur in mutually exclusive spatial regions. This conclusion is also supported by our recent oxygen isotope effect experiments in LBCO-1/8 [2]. Another interesting issue we studied with µSR is the suppression of magnetism and the occurrence of superconductivity in CrAs as a function of pressure [3]. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 ≤ p ≤ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. A scaling of the superfluid density with Tc3.2 as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. [1] Z. Guguchia et al., New Journal of Physics 15, 093005 (2013). [2] Z. Guguchia et al., Phys. Rev. Lett. 113, 057002 (2014). [3] R. Khasanov, Z. Guguchia et. al., arXiv:1502.07573v1 (2015).

Authors : Alexandros Lappas (1), Andrej Zorko (2), Denis Arcon (2)
Affiliations : (1) Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, Vassilika Vouton, 71110 Heraklion, Greece; (2) Jozef Stefan Institute, Jamova c. 39, 1000 Ljubljana, Slovenia

Resume : Competition in chemically homogeneous strongly correlated transition-metal oxides leads to electronic-phase inhomogeneities on the nanoscale and amongst others to fascinating magnetoresisitve and superconducting states. In this respect, the frustrated spatially-anisotropic triangular-lattice antiferromagnet NaMnO2 is challenging as it features unexpected coexistence of long- and short- range magnetic correlations below TN = 45 K. Our complementary high-resolution synchrotron XRD, local-probe 23Na NMR and muon-spin relaxation (μ+SR) studies, corroborate that the layered NaMnO2 adopts a remarkable magnetostructurally inhomogeneous ground state in the absence of active charge degrees of freedom [1]. We show that two major opposing effects (elastic vs. magnetic exchange) of similar magnitude, lead to nearly equivalent, competing structural phases, which enable infinitesimal quenched disorder to locally lift the inherent frustration of the parent monoclinic phase. To provide an insight to this puzzling phase separation we have extended our study to the isomorphous CuMnO2 (TN = 65 K) compound, where local probes suggest that the interlayer cation (Cu) mediates the transition to a less inhomogeneous ground state [2]. NaMnO2 provides a paradigm of a rarely observed nanoscale inhomogeneity in an insulating spin system, an intriguing complexity of competition due to geometrical frustration. [1] A. Zorko et al., Nat. Commun. 5, 3222 (2014) [2] A. Zorko et al., Sci. Rep. 5, 9272 (2015)

Authors : Tomasz Story
Affiliations : Institute of Physics PAS, Warsaw, Poland

Resume : Electron crystal - phonon glass concept of modern thermoelectrics was technologically and experimentally verified in semiconductor bulk two-phase crystalline nanocomposites (Pb,Cd)Te-CdTe and in multilayer quantum-dot PbTe-CdTe nanostructures. Very low mutual solubility of lattice-matched rock-salt PbTe and zinc-blende CdTe crystals makes this system a model thermoelectric nanocomposite of zinc-blende CdTe nano-dots epitaxially embedded in a rock-salt PbTe thermoelectric crystalline matrix. We observed these nano structures forming spontaneously in properly annealed bulk crystals as well as developed the technological procedure of growing the PbTe-CdTe multilayer quantum-dot nanostructures by molecular beam epitaxy method controlling the size (from 5 to 30 nm) and distribution of CdTe dots. The n-type PbTe-CdTe multilayer with the smallest CdTe dots revealed at room temperature an increase of thermoelectric power as compared to reference bulk n-PbTe crystals. In PbTe-CdTe bulk nanostructures doped with Bi or Na we found an increased thermoelectric power and a reduced thermal conductivity resulting in very good ZT thermoelectric figure of merit parameter up to 0.9 at T=700 K for both n- and p-type materials. M. Szot et al., Functional Materials Lett. 7, 1440007 (2014). Work supported by the European Regional Development Fund through the Innovative Economy grant (POIG.01.01.02-00-108/09).


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Symposium organizers
Tomasz DIETLInternational Research Centre MagTop

al. Lotnikow 32/46; PL-02668 Warszawa; Poland

+48 22 1163264
Manfred HELMHelmholtz-Zentrum Dresden-Rossendorf - Institute of Ion Beam Physics and Materials Research

Bautzner Landstraße 400 D-01328 Dresden Germany

+49 351 260 - 2260
Krzysztof ROGACKIInstitute of Low Temperature and Structural Research

ul. Okólna 2 PL- 50-422 Wrocław Poland

+48 71 3954 317