Absence of ferromagnetism in V-implanted ZnO single crystals

The structural and magnetic properties of V doped ZnO are presented. V ions were introduced into hydrothermal ZnO single crystals by ion implantation with fluences of 1.2*10^16 to 6*10^16 cm^-2. Post-implantation annealing was performed in high vacuum from 823 K to 1023 K. The ZnO host material still partly remains in a crystalline state after irradiation, and is partly recovered by annealing. The V ions show a thermal mobility as revealed by depth profile Auger electron spectroscopy. Synchrotron radiation x-ray diffraction revealed no secondary phase formation which indicates the substitution of V onto Zn site. However in all samples no pronounced ferromagnetism was observed down to 5 K by a superconducting quantum interference device magnetometer.Comment: 13 pages, 4 figs, MMM conference 2007, accepted by J. Appl. Phy

MnSi1.7_{1.7} nanoparticles embedded in Si: Superparamagnetism with a collective behavior

The doping of Mn in Si is attracting research attentions due to the possibility to fabricate Si-based diluted magnetic semiconductors. However, the low solubility of Mn in Si favors the precipitation of Mn ions even at non-equilibrium growth conditions. MnSi$_{1.7}$ nanoparticles are the common precipitates, which show exotic magnetic properties in comparison with the MnSi$_{1.7}$ bulk phase. In this paper we present the static and dynamic magnetic properties of MnSi$_{1.7}$ nanoparticles. Using the Preisach model, we derive the magnetic parameters, such as the magnetization of individual particles, the distribution of coercive fields and the inter-particle interaction field. Time-dependent magnetization measurements reveal a spin-glass behavior of the system.Comment: 11 pages, 6 figures, submitted to PR

Doctors, Lawyers and advance care planning: Time for innovation to work together to meet client needs

Health organizations in Canada have invested considerable resources in strategies to improve knowledge and uptake of advance care planning (ACP). Yet barriers persist and many Canadians do not engage in the full range of ACP behaviours, including writing an advance directive and appointing a legally authorized decision-maker. Not engaging effectively in ACP disadvantages patients, their loved ones and their healthcare providers. This article advocates for greater collaboration between health and legal professionals to better support clients in ACP and presents a framework for action to build connections between these typically siloed professions

Improved Robustness for Numerical Simulation of Turbulent Flows around Civil Transport Aircraft at Flight Reynolds Numbers

This work aims at providing numerical methods that enable the robust and efficient simulation of turbulent flows around civil transport aircraft configurations at flight Reynolds numbers. The combined utilization of a computational and a theoretical approach for the systematic investigation of the numerical treatment of turbulence equations characterizes the work at hand. Robustness problems in case of multigrid treatment of advanced transport equation turbulence models have been identified to prevent convergence of simulations at high or flight Reynolds numbers. Therefore the application of multigrid to the turbulence equations is omitted while the multigrid treatment of the RANS equations stays unchanged. Moreover, a fully implicit time integration scheme - a DDADI approach - is applied to the turbulence equations. This approach was inspired by a systematic investigation of the numerical treatment of turbulence equations utilizing two dimensional computations and Fourier analyses. This study clearly demonstrated a destabilizing effect of productive (turbulence) source terms which is amplified in the framework of multigrid. Finally, both the original and the improved FLOWer code has been applied to two and three dimensional test cases of industrial relevance and the respective results are compared. The new approach raised robustness to a sufficient niveau to converge viscous computations at flight Reynolds numbers. Furthermore, the convergence speed of aerodynamic coefficients for three dimensional applications has also been improved significantly.Zielsetzung dieser Arbeit ist die Bereitstellung numerischer Verfahren, die eine robuste und effiziente Simulation turbulenter Strömungen für zivile Transportflugzeugskonfigurationen bei Flug-Reynolds-Zahlen ermöglichen. Diese Arbeit zeichnet sich dadurch aus, dass sie für die systematische Untersuchung der numerischen Behandlung von Turbulenz- gleichungen den Einsatz von Simulationsrechnungen und theoretischen Ansätzen kombiniert. Robustheitsprobleme, welche die Konvergenz von Simulationen bei hohen und bei Flug-Reynolds-Zahlen verhindern, konnten auf die Anwendung eines Mehrgitter-Verfahrens auf Transportgleichungsturbulenzmodelle zurückgeführt werden. Daher ist das Mehrgitter-Verfahren für die Turbulenzgleichungen abgeschaltet worden, während sein Einsatz für die RANS-Gleichungen nicht verändert wurde. Desweiteren ist ein voll implizites Zeitintegrationsverfahren – ein DDADI Ansatz – auf die Turbulenzgleichungen angewendet worden. Die Herleitung dieses Ansatzes basiert auf einer systematischen Untersuchung der numerischen Behandlung von Turbulenzgleichungen. Hierfür wurden zweidimensionale Simulationsrechnungen und Fourier- Analysen durchgeführt. Die Studie hat deutlich einen destabilisierenden Effekt produktiver (Turbulenz-)Quellterme gezeigt, der im Rahmen von Mehrgitter-Verfahren verstärkt wird. Abschließend wurden sowohl der originale FLOWer-Code als auch die verbesserte Variante auf zwei- und dreidimensionale industriell relevante Testfälle angewendet und die Ergebnisse verglichen. Der neue Ansatz liefert eine deutliche Steigerung der Robustheit, aufgrund derer viskose Simulationsrechnungen bei Flug-Reynolds-Zahlen konvergieren. Darüber hinaus ist die Konvergenz der aerodynamischen Koeffizienten für dreidimensionale Anwendungen deutlich beschleunigt worden

Origin of magnetic moments in defective TiO2 single crystals

In this paper we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman-scattering, and electron spin resonance spectroscopy, a defect complex, \emph{i.e.} Ti$^{3+}$ ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a local (TiO$_{6-x}$) stretching Raman mode. We elucidate that Ti$^{3+}$ ions with one unpaired 3d electron provide the local magnetic moments.Comment: 4 pages, 4 figures, to be published at Phys. Rev.

Crystallographically oriented Co and Ni nanocrystals inside ZnO formed by ion implantation and postannealing

In the last decade, transition-metal-doped ZnO has been intensively investigated as a route to room-temperature diluted magnetic semiconductors (DMSs). However, the origin for the reported ferromagnetism in ZnO-based DMS remains questionable. Possible options are diluted magnetic semiconductors, spinodal decomposition, or secondary phases. In order to clarify this question, we have performed a thorough characterization of the structural and magnetic properties of Co- and Ni-implanted ZnO single crystals. Our measurements reveal that Co or Ni nanocrystals (NCs) are the major contribution of the measured ferromagnetism. Already in the as-implanted samples, Co or Ni NCs have formed and they exhibit superparamagnetic properties. The Co or Ni NCs are crystallographically oriented with respect to the ZnO matrix. Their magnetic properties, e.g., the anisotropy and the superparamagnetic blocking temperature, can be tuned by annealing. We discuss the magnetic anisotropy of Ni NCs embedded in ZnO concerning the strain anisotropy.Comment: 13 pages, 14 figure