63 research outputs found
Current-driven vortex oscillations in metallic nanocontacts
We present experimental evidence of sub-GHz spin-transfer oscillations in
metallic nano-contacts that are due to the translational motion of a magnetic
vortex. The vortex is shown to execute large-amplitude orbital motion outside
the contact region. Good agreement with analytical theory and micromagnetics
simulations is found.Comment: 4 pages, 3 figure
Current-driven microwave oscillations in current perpendicular-to-plane spin-valve nanopillars
We study the current and temperature dependences of the microwave voltage
emission of spin-valve nanopillars subjected to an in-plane magnetic field and
a perpendicular-to-plane current. Despite the complex multilayer geometry,
clear microwave emission is shown to be possible and spectral lines as narrow
as 3.8 MHz (at 150 K) are observed.Comment: To appear in Applied Physics Letter
Large microwave generation from d.c. driven magnetic vortex oscillators in magnetic tunnel junctions
Spin polarized current can excite the magnetization of a ferromagnet through
the transfer of spin angular momentum to the local spin system. This pure
spin-related transport phenomena leads to alluring possibilities for the
achievement of a nanometer scale, CMOS compatible and tunable microwave
generator operating at low bias for future wireless communications. Microwave
emission generated by the persitent motion of magnetic vortices induced by spin
transfer effect seems to be a unique manner to reach appropriate spectral
linewidth. However, in metallic systems, where such vortex oscillations have
been observed, the resulting microwave power is much too small. Here we present
experimental evidences of spin-transfer induced core vortex precessions in
MgO-based magnetic tunnel junctions with similar good spectral quality but an
emitted power at least one order of magnitude stronger. More importantly,
unlike to others spin transfer excitations, the thorough comparison between
experimental results and models provide a clear textbook illustration of the
mechanisms of vortex precessions induced by spin transfer
Psychometric properties of the Community Mental Health Team effectiveness questionnaire (CMHTEQ)
Communicating Auditory Impairments Using Electroacoustic Composition
Changes in human sensory perception can occur for a variety of reasons. In the case of distortions or transformations in the human auditory system, the aetiology may include factors such as medical conditions affecting cognition or physiology, interaction of the ears with mechanical waves, or stem from chemically induced sources, such the consumption of alcohol. These changes may be permanent, intermittent, or temporary. In order to communicate such effects to an audience in an accessible, and easily understood manner, a series of electroacoustic compositions were produced. This concept follows on from previous work on the theme of representing auditory hallucinations. Specifically, these compositions relate to auditory impairments that humans can experience due to tinnitus or through the consumption of alcohol. In the case of tinnitus, whilst much is known about the causes and symptoms, the experience of what it is like to live with tinnitus is less explored and those who have acquired the condition may often feel frustration when trying to convey the experience of ‘what it is like’ for them. In terms of impairment from alcohol consumption, whilst there is much hearsay, little research exists on the immediate and short-term effects of alcohol consumption on the human auditory system, despite over half of the UK population reported as consuming alcohol in 2017. The methodology employed to design these compositions draws upon scientific research findings, including experimental and explorative studies involving human participants, coupled with electroacoustic composition techniques. The pieces are typically constructed by mixing field recordings with synthesised materials and incorporating a range of temporal and frequency domain manipulations to the elements therein. In this way, the listener is able to experience the phenomenon in a recognisable context, where distortions of reality can be emulated to varying degrees. It is intended that these compositions can serve as easily accessible and understood examples of auditory impairments and that they might find utility in the communication of symptoms to those who have never experienced the underlying causes or conditions. This presents opportunities for pieces like these to be used in scenarios such as education and public health awareness campaigns
Nanoscale switch for vortex polarization mediated by Bloch core formation in magnetic hybrid systems
Vortices are fundamental magnetic topological structures characterized by a curling magnetization around a highly stable nanometric core. The control of the polarization of this core and its gyration is key to the utilization of vortices in technological applications. So far polarization control has been achieved in single-material structures using magnetic fields, spin-polarized currents or spin waves. Here we demonstrate local control of the vortex core orientation in hybrid structures where the vortex in an in-plane Permalloy film coexists with out-of-plane maze domains in a Co/Pd multilayer. The vortex core reverses its polarization on crossing a maze domain boundary. This reversal is mediated by a pair of magnetic singularities, known as Bloch points, and leads to the transient formation of a three-dimensional magnetization structure: a Bloch core. The interaction between vortex and domain wall thus acts as a nanoscale switch for the vortex core polarization
Present international patterns of foreign direct investment: underlying causes and some policy implications for Brazil
Impact of the nature of the compliant electrodes on the dielectric constant of acrylic and silicone electroactive polymers
International audienceDielectric elastomers are emerging electroactive materials used in high performance applications such as robots, artificial muscles and energy harvesting. The development of such applications requires the use of accurate, predictive, reliable models which take into account the dielectric constant (permittivity) of these materials. This dielectric constant is not clearly defined for such applications and depends on many parameters. This leads to values dispersed in the literature for the same electroactive polymer. This paper shows that the nature of the compliant electrodes can influence this dielectric constant significantly. However, the reduction generally observed in this permittivity according to the stretching of elastomer cannot be imputed to the nature of these electrodes, and rather confirms an effect of the volume of the elastomer. This tends to prove that the influence of the compliant electrode is located at the electrode-elastomer interfaces. In addition, the nature of the metallic particles embedded in the electrode grease seems not to influence the value of the dielectric constant. Lastly, we propose analytic laws to describe changes of the dielectric constant as a function of the temperature and the deformation of the material. This makes it possible to define new limits of operation for these polymers for actuators and energy harvesting applications
Advances for dielectric elastomer generators: Replacement of high voltage supply by electret
International audienceDielectric generators require an external circuit with a high bias voltage source to polarize them. To drastically reduce this circuit and to avoid external polarization, we propose here original transducers combining electrets and dielectric elastomer. Two operating modes have been studied and electromechanical analytical models have been developed from the combination of electrets theory and dielectric model. These concepts are applied on e-textile application: scavenging energy during human motion. An energy density around 6 mJ g 1 is expected on an optimal load of 10 MX. More generally, the flexibility, the lightness, the absence of high-voltage supply open many fields of applications beyond e-textiles
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