Search results for "Metals"
showing 10 items of 2013 documents
Dzyaloshinskii-Moriya Interaction and Hall Effects in the Skyrmion Phase ofMn1−xFexGe
2015
We carry out density functional theory calculations which demonstrate that the electron dynamics in the Skyrmion phase of Fe-rich Mn_{1-x}Fe_{x}Ge alloys is governed by Berry phase physics. We observe that the magnitude of the Dzyaloshinskii-Moriya interaction directly related to the mixed space-momentum Berry phases, changes sign and magnitude with concentration x in direct correlation with the data of Shibata et al. [Nat. Nanotechnol. 8, 723 (2013)]. The computed anomalous and topological Hall effects in FeGe are also in good agreement with available experiments. We further develop a simple tight-binding model able to explain these findings. Finally, we show that the adiabatic Berry phase…
Beyond the Vegard's law: solid mixing excess volume and thermodynamic potentials prediction, from end-members
2020
Abstract A method has been developed, herein presented, to model binary solid solutions' volume, enthalpy and Gibbs energy using the energy state functions, E ( V , S ) , of the end-members only. The E ( V , S ) s are expanded around an unknown mixing volume, V Mix , and the fundamental equilibrium equation − ( ∂ E / ∂ V ) S = P is used to determine V Mix . V Mix allows us to model enthalpy, straightforwardly. The same argument holds using Helmholtz energy, F ( V , T ) , in place of E ( V , S ) , and the equilibrium equation becomes − ( ∂ F / ∂ V ) T = P . One can readily determine the Gibbs free energy, too. The method presented remarkably simplifies computing of solid mixings' thermodynam…
Theory of vibrational anomalies in glasses
2015
Abstract The theory of elasticity with spatially fluctuating elastic constants (heterogeneous-elasticity theory) is reviewed. It is shown that the vibrational anomalies associated with the boson peak can be qualitatively and quantitatively explained in terms of this theory. Two versions of a mean-field theory for solving the stochastic equation of motion are presented: the coherent-potential approximation (CPA) and the self-consistent Born approximation (SCBA). It is shown that the latter is included in the former in the Gaussian and weak-disorder limit. We are able to discuss and explain cases in which the change of the vibrational spectrum by varying an external parameter can be accounted…
CONDENSATION OF REFRACTORY METALS IN ASYMPTOTIC GIANT BRANCH AND OTHER STELLAR ENVIRONMENTS
2014
The condensation of material from a gas of solar composition has been extensively studied, but less so condensation in the environment of evolved stars, which has been mainly restricted to major compounds and some specific element groups such as the Rare Earth elements. Also of interest, however, are refractory metals like Mo, Ru, Os, W, Ir, and Pt, which may condense to form refractory metal nuggets (RMNs) like the ones that have been found in association with presolar graphite. We have performed calculations describing the condensation of these elements in the outflows of s-process enriched AGB stars as well as from gas enriched in r-process products. While in carbon-rich environments (C …
Cluster growth with long-range interactions
1996
Abstract Growth models in which the morphology depends on interactions of the type V(r) = C r n are presented. The growth algorithms are generalizations of DLA. The particles diffuse on a triangular lattice and eventually either stick to the cluster or are lost. Several processes are simulated in this way: in one case only pure sticking is taken into account, in another case evaporation and rearrangement are also allowed to occur. In the former case (with attractive interactions) the clusters exhibit a highly symmetric shape (a sixfold star) whose detailed structure depends on n , C kT , and time. In the latter case (studied with repulsive dipolar interactions) the tendency to ramification …
Brief encounter at the molecular level: what muons tell us about molecule-based magnets
2005
Abstract Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin–1/2, a lifetime of 2.2 μ S , about one-ninth of the proton mass and a magnetic moment of approximately 1/200 μ B . Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a…
Operation of transition-edge sensors with excess thermal noise
2006
The superconducting transition-edge sensor (TES) is currently one of the most attractive choices for ultra-high resolution calorimetry in the keV x-ray band, and is being considered for future ESA and NASA missions. We have performed a study on the noise characteristics of Au/Ti bilayer TESs, at operating temperatures around ~100 mK, with the SQUID readout at 1.5 K. Experimental results indicate that without modifications the back-action noise from the SQUID chip degrades the noise characteristics significantly. We present a simple and effective solution to the problem: by installing an extra shunt resistor which absorbs the excess radiation from the SQUID input, we have reduced the excess …
First measurement of radioisotopes by collinear laser spectroscopy at an ion-guide separator
1997
The first successful application of an ion-guide separator (IGISOL) for collinear laser spectroscopy of radioisotopes has achieved an efficiency comparable with the best obtained with catcher-ionizer facilities. The ion beam energy spread was determined to be less than 6 eV, allowing laser fluorescence resonance signals for the Ba-140,Ba-142,Ba-144 radioisotopes to be detected with high resolution and sensitivity. Applications of this technique to measuring nuclear properties of refractory elements and short lived isomers promises to be particularly advantageous.
New ion-guide for the production of beams of neutron-rich nuclei between Z=20–28
2005
It has been shown for the first time that quasi- and deep-inelastic reactions can be successfully incorporated into the conventional Ion-Guide Isotope Separator On-Line (IGISOL) technique. This is of particular interest for characterizing the decay properties of refractory elements and is applied to neutron rich nuclei between Z = 20-28. As a first step of this project, the kinematics of quasi- and deep-inelastic reactions, such as {sup 197}Au({sup 65}Cu,X)Y, were studied. Based on these studies, a specialized IGISOL target chamber was designed and built. This chamber was tested in on- and off-line conditions at the Jyvaskyla IGISOL facility. Yields of radioactive, projectile-like species s…
Nonadiabatic quantum search algorithms
2007
7 pages, 4 figures.-- PACS nrs.: 03.67.Lx, 05.45.Mt, 72.15.Rn.-- ISI Article Identifier: 000251326400049.-- ArXiv pre-print available at: http://arxiv.org/abs/0706.1139