Reduction of magnetostatic interactions in self-organized arrays of nickel nanowires using atomic layer deposition

Ordered arrays of magnetic nanowires are commonly synthesized by electrodeposition in nanoporous alumina templates. Due to their dense packing, strong magnetostatic interactions prevent the manipulation of wires individually. Using atomic layer deposition we reduce the diameter of the pores prior to electrodeposition. This reduces magnetostatic interactions, yielding fully remanent hysteresis loops. This is a first step towards the use of such arrays for magnetic racetrack memories

The skyrmion-bubble transition in a ferromagnetic thin film

Magnetic skyrmions and bubbles, observed in ferromagnetic thin films with perpendicular magnetic anisotropy, are topological solitons which differ by their characteristic size and the balance in the energies at the origin of their stabilisation. However, these two spin textures have the same topology and a continuous transformation between them is allowed. In the present work, we derive an analytical model to explore the skyrmion-bubble transition. We evidence a region in the parameter space where both topological soliton solutions coexist and close to which transformations between skyrmion and bubbles are observed as a function of the magnetic field. Above a critical point, at which the energy barrier separating both solutions vanishes, only one topological soliton solution remains, which size can be continuously tuned from micrometer to nanometer with applied magnetic field

La Grèce et l'Europe : une intégration paradoxale

L'intégration de la Grèce à l'Europe communautaire en 1981 a eu des effets remarquables sur le développement du pays. Le redressement socio-économique spectaculaire opéré en quelques années a bouleversé les paysages et transformé les mentalités. L'analyse comparée des principaux indicateurs statistiques par rapport aux autres Etats européens est un moyen efficace de mesurer les progrès réalisés. Face aux impératifs de normalisation bruxellois, la Grèce a fait preuve de capacités d'adaptation étonnantes sans renier son héritage culturel propre. Le positionnement géopolitique d'Athènes face à une péninsule balkanique meurtrie par des années de conflits et de crises économiques à répétition sera éclairé à la lumière de ces changements

Coupling efficiency for phase locking of a spin transfer oscillator to a microwave current

The phase locking behavior of spin transfer nano-oscillators (STNOs) to an external microwave signal is experimentally studied as a function of the STNO intrinsic parameters. We extract the coupling strength from our data using the derived phase dynamics of a forced STNO. The predicted trends on the coupling strength for phase locking as a function of intrinsic features of the oscillators i.e. power, linewidth, agility in current, are central to optimize the emitted power in arrays of mutually coupled STNOs

Observation of Bloch-point domain walls in cylindrical magnetic nanowires

Topological protection is an elegant way of warranting the integrity of quantum and nanosized systems. In magnetism one example is the Bloch-point, a peculiar object implying the local vanishing of magnetization within a ferromagnet. Its existence had been postulated and described theoretically since several decades, however it has never been observed. We con rm experimentally the existence of Bloch points, imaged within domain walls in cylindrical magnetic nanowires, combining surface and transmission XMCD-PEEM magnetic microscopy. This opens the way to the experimental search for peculiar phenomena predicted during the motion of Bloch-point-based domain walls

Formation of Atomic-Sized Contacts by Electrochemical Methods

Electrochemical methods have recently become an interesting tool for fabricating and characterizing nanostructures at room temperature. Simplicity, low cost and reversibility are some of the advantages of this technique that allows to work at the nanoscale without requiring sophisticated instrumentation. In our experimental setup, we measure the conductance across a nanocontact fabricated either by dissolving a macroscopic gold wire or by depositing gold in between two separated gold electrodes. We have achieved a high level of control on the electrochemical fabrication of atomic-sized contacts in gold. The use of electrochemistry as a reproducible technique to prepare nanocontacts will open several possibilities that are not feasible with other methodologies. It involves, also, the possibility of reproducing experiments that today are made by more expensive, complicated or irreversible methods. As example, we show here a comparison of the results when looking for shell effects in gold nanocontacts with those obtained by other techniques.Comment: 7 pages, 5 figures, submitted to PS

What static and dynamic properties should slalom skis possess? Judgments by advanced and expert skiers

Flexural and torsional rigidity are important properties of skis. However, the flexural and torsional rigidity that lead to optimal performance remain to be established. In the present study, four pairs of slalom skis that differed in flexural and torsional rigidity were tested by advanced and expert skiers. Using a 10-item questionnaire, different aspects of the skis’ performance were rated on a 9-point scale. For each pair of skis, physical measurements were compared with the ratings of the two groups of skiers. Correlations (Spearman) were then determined between (i) different mechanical properties of the skis (static and dynamic), (ii) subjective assessments of the participants, and (iii) properties of the skis and the participants’ assessments. The latter showed that expert skiers rate the aspects of the skis more accurately than advanced skiers. Importantly, expert skiers are particularly sensitive to torsion of the skis. These results suggest that such highly rated elements should be addressed in future ski designs

Effect of Crystallographic Texture on Magnetic Characteristics of Cobalt Nanowires

Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition in etched ion-track polycarbonate membranes. Structural characterization of these nanowires with diameter 70, 90, 120 nm and length 30 μm was performed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. The as-prepared wires show uniform diameter along the whole length and X-ray diffraction analysis reveals that [002] texture of these wires become more pronounced as diameter is reduced. Magnetic characterization of the nanowires shows a clear difference of squareness and coercivity between parallel and perpendicular orientations of the wires with respect to the applied field direction. In case of parallel applied field, the coercivity has been found to be decreasing with increasing diameter of the wires while in perpendicular case; the coercivity observes lower values for larger diameter. The results are explained by taking into account the magnetocrystalline and shape anisotropies with respect to the applied field and domain transformation mechanism when single domain limit is surpassed

Are There Critical Fatigue Thresholds? Aggregated vs. Individual Data

The mechanisms underlying task failure from fatiguing physical efforts have been the focus of many studies without reaching consensus. An attractive but debated model explains effort termination with a critical peripheral fatigue threshold. Upon reaching this threshold, feedback from sensory afferents would trigger task disengagement from open-ended tasks or a reduction of exercise intensity of closed-ended tasks. Alternatively, the extant literature also appears compatible with a more global critical threshold of loss of maximal voluntary contraction force. Indeed, maximal voluntary contraction force loss from fatiguing exercise realized at a given intensity appears rather consistent between different studies. However, when looking at individual data, the similar maximal force losses observed between different tasks performed at similar intensities might just be an "artifact" of data aggregation. It would then seem possible that such a difference observed between individual and aggregated data also applies to other models previously proposed to explain task failure from fatiguing physical efforts. We therefore suggest that one should be cautious when trying to infer models that try to explain individual behavior from aggregated data