Hysteresis and Spikes in the Quantum Hall Effect

We observe sharp peaks and strong hysteresis in the electronic transport of a two-dimensional electron gas (2DEG) in the region of the integral quantum Hall effect. The peaks decay on time scales ranging from several minutes to more than an hour. Momentary grounding of some of the contacts can vastly modify the strength of the peaks. All these features disappear under application of a negative bias voltage to the backside of the specimen. We conclude, that a conduction channel parallel to the high mobility 2DEG is the origin for the peaks and their hysteretic behavior.Comment: 7 pages, 3 eps figures. Submitted to Phys. Rev. Lett, minor typos correcte

Theory of Thermal Remagnetization of Permanent Magnets

A self-consistent mean-field theory explaining the thermal remagnetization (TR) of polycrystalline permanent magnets is given. The influence of the environment of a grain is treated by an inclusion approximation, relating the field inside the grain to the local field outside by means of an internal demagnetization factor $n$. For the switching fields and the fluctuations of the local fields around the mean field Gaussian distributions of widths \sigmas and \sigmaf resp. are assumed. The isothermal hysteresis curve, the recoil curves, and the TR in dependence on the model parameters $n$, \sigmas, and \sigmaf are calculated. Furthermore, the influence of the initial temperature and the strong dependence of the TR on the demagnetization factor of the sample are studied, and it is shown that for reasonable parameter sets TR effects up to 100 % are possible. The theoretical results correspond well with the experimental situation.Comment: 28 pages, 9 figures, Latex2e, accepted for publication in JMM

Charge screening and magnetic anisotropy in metallic rare-earth systems

The calculation of magnetic anisotropy constants is performed beyond the point charge model for a continuous charge density distribution of screening conduction electrons. An important role of the non-uniform electron density, in particular, of the Friedel oscillations, in the formation of crystal field is demonstrated. Such effects can modify strongly the effective ion (impurity) charge and even change its sign. This enables one to justify the anion model, which is often used at discussing experimental data on hydrogen-containing systems. Possible applications to the pure rare-earth metals and RCo5 compounds are discussed. The deformation of magnetic structure near the interstitial positive muon owing to the strong local anisotropy, and the corresponding contribution to the dipole field at the muon are considered.Comment: 10 pages, RevTeX, 3 figure

Fast stray field computation on tensor grids

A direct integration algorithm is described to compute the magnetostatic field and energy for given magnetization distributions on not necessarily uniform tensor grids. We use an analytically-based tensor approximation approach for function-related tensors, which reduces calculations to multilinear algebra operations. The algorithm scales with N^(4/3) for N computational cells used and with N^(2/3) (sublinear) when magnetization is given in canonical tensor format. In the final section we confirm our theoretical results concerning computing times and accuracy by means of numerical examples.Comment: 16 pages, 1 figure, submitted to the Journal of Computational Physic

Fe and N self-diffusion in amorphous FeN: A SIMS and neutron reflectivity study

Simultaneous measurement of self-diffusion of iron and nitrogen in amorphous iron nitride (Fe86N14) using secondary ion mass spectroscopy (SIMS) technique has been done. In addition neutron reflectivity (NR) technique was employed to study the Fe diffusion in the same compound. The broadening of a tracer layer of 57Fe8615N14 sandwiched between Fe86N14 layers was observed after isothermal vacuum annealing of the films at different temperatures in SIMS measurements. And a decay of the Bragg peak intensity after isothermal annealing was observed in [Fe86N14/57Fe86N14]10 multilayers in NR. Strong structural relaxation of diffusion coefficient was observed below the crystallization temperature of the amorphous phase in both measurements. It was observed from the SIMS measurements that Fe diffusion was about 2 orders of magnitude smaller compared to nitrogen at a given temperature. The NR measurements reveal that the mechanism of Fe self-diffusion is very similar to that in metal-metal type metallic glasses. The structural relaxation time for Fe and N diffusion was found comparable indicating that the obtained relaxation time essentially pertain to the structural relaxation of the amorphous phase.Comment: 10 pages 12 figure

Verfahren zur Optimierung der Ziehgeschwindigkeit einer Rohrziebank

Available from TIB Hannover: RR 4652(17) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Show me the pragmatic contribution: a developmental investigation of contrastive inference

International audienceAn utterance such as 'Show me the large rabbit' potentially generates a CONTRASTIVE INFERENCE, i. e., the article the and the adjective large allow listeners to pragmatically infer the existence of other entities having the same noun (e. g. a small rabbit). The primary way to measure children's ability to carry out this pragmatic inference has been through tasks that measure infelicity detection. We argue that such studies are not as revealing as one might assume because they force children to adopt a metalinguistic stance and they consider infelicity detection as tantamount to contrastive inference-making. To address these concerns, we develop a game-like situation in which all utterances remain felicitous. Moreover, we make a distinction between responses that are revealing of a pragmatic interpretation and responses that are revealing of a reliance on the utterance's LINGUISTICALLY ENCODED meaning (i. e., a lack of contrastive inference). Three experiments with seven-year-olds, ten-year-olds, and adults show that pragmatic interpretations do not emerge among seven-year-olds, that ten-year-olds do not show adult-like performance, and that adults are not at ceiling. We conclude that contrastive inference-making is an effortful process and that the ability to detect such gains-in-information through language increases with age

Sichtbarmachung der Flussverteilung in Hochtemperatursupraleitern nach verschiedenen Mikrostrukturaenderungen Abschlussbericht

Theoretical calculation models for current, magnetic and electric field distributions in thin superconductors of arbitrary shape in perpendicular magnetic field were developed. Calculations were done for inhomogeneous and anisotropic critical currents and compared with magnetooptical observations of flux penetration. Nice agreement of theory and experiment was found. Flux-line depinning and motion in superconductors with linear defects was investigated by magneto-optics. Depinning mechanisms were deduced from observations of high-temperature superconductors which are irradiated with swift heavy ions parallel and crosswisely at various angles to the surface normal. Magneto-optical investigations of flux penetration into (Bi,Pb)_2Sr_2Ca_2Cu_3O_1_0_+_#delta# multifilament tapes showed a strong dependence of the current capability on the microstructure of single filaments. The different filament textures which are caused by the inhomogeneous deformation of the tape during thermomechanical treatment results in critical current densities varying by about one order of magnitude. (orig.)Theoretische Modelle zur Berechnung von Strom-, Magnet- und elektrischen Feldverteilungen wurden fuer duenne Supraleiter beliebiger Geometrie mit inhomogener und anisotroper kritischer Stromdichte im senkrechten Magnetfeld entwickelt und mit magnetooptischen Beobachtungen des Flusseindringens verglichen, wobei eine hervorragende Uebereinstimmung zwischen Theorie und Experiment erzielt wurde. Mit Hilfe von magnetooptischen Untersuchungen des Flusseindringens in schwerionenbestrahlte Hochtemperatursupraleiter, die unter verschiedenen Winkeln zur Oberflaechennormalen parallel und kreuzweise bestrahlt wurden, konnten Bewegungs- und Entankerungsmechanismen von Flusslinien in Supraleitern mit linearen Defekten abgeleitet werden. Magnetooptische Untersuchungen des Flusseindringens in (Bi, Pb)_2Sr_2Ca_2Cu_3O_1_0_+_#delta#-Multifilamentbandleiter zeigten, dass die Stromtragfaehigkeit sehr stark von der Mikrostruktur der einzelnen Filamente abhaengt. Die unterschiedliche Textur der Filamente, die aufgrund der inhomogenenen Verformung waehrend der thermomechanischen Behandlung entsteht, erzeugt Unterschiede in der kritischen Stromdichte von etwa einer Groessenordnung. (orig.)SIGLEAvailable from TIB Hannover: F98B1133+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman