146 research outputs found
Agility of vortex-based nanocontact spin torque oscillators
We study the agility of current-tunable oscillators based on a magnetic
vortex orbiting around a point contact in spin-valves. Theory predicts
frequency-tuning by currents occurs at constant orbital radius, so an
exceptional agility is anticipated. To test this, we have inserted an
oscillator in a microwave interferometer to apply abrupt current variations
while time resolving its emission. Using frequency shift keying, we show that
the oscillator can switch between two stabilized frequencies differing by 25%
in less than ten periods. With a wide frequency tunability and a good agility,
such oscillators possess desirable figures of merit for modulation-based rf
applications.Comment: 3 pages, 3 figure
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
Auto-oscillation threshold and line narrowing in MgO-based spin-torque oscillators
We present an experimental study of the power spectrum of current-driven
magnetization oscillations in MgO tunnel junctions under low bias. We find the
existence of narrow spectral lines, down to 8 MHz in width at a frequency of
10.7 GHz, for small applied fields with clear evidence of an auto-oscillation
threshold. Micromagnetics simulations indicate that the excited mode
corresponds to an edge mode of the synthetic antiferromagnet
Atomistic study on the pressure dependence of the melting point of NdFe12
We investigated, using molecular dynamics, how pressure affects the melting point of the recently theorised and epitaxially grown structure NdFe12. We modified Morse potentials using experimental constants and a genetic algorithm code, before running two-phase solid-liquid coexistence simulations of NdFe12 at various temperatures and pressures. The refitting of the Morse potentials allowed us to significantly improve the accuracy in predicting the melting temperature of the constituent elements
Current-driven vortex oscillations in metallic nanocontacts: Zero-field oscillations and training effects
We present an experimental and theoretical study of the low-field dynamics of
current-driven vortex oscillations in nanocontacts based on spin-valve
multilayers. These oscillations appear as low-frequency (250-500 MHz)
excitations in the electrical power spectrum which arise from to variations in
the giant-magnetoresistance. We show that the vortex oscillations, once
nucleated at large fields applied perpendicular to the film plane, persist at
zero applied magnetic fields. Some training effects on the oscillation
frequency and linewidth also observed for small in-plane magnetic fields.Comment: 6 pages, 7 figure
Striving towards Near Real-Time Data Integration for Data Warehouses
Abstract. The amount of information available to large-scale enterprises is growing rapidly. While operational systems are designed to meet well-specified (short) response time requirements, the focus of data warehouses is generally the strategic analysis of business data integrated from heterogeneous source systems. The decision making process in traditional data warehouse environments is often delayed because data cannot be propagated from the source system to the data warehouse in time. A real-time data warehouse aims at decreasing the time it takes to make business decisions and tries to attain zero latency between the cause and effect of a business decision. In this paper we present an architecture of an ETL environment for real-time data warehouses, which supports a continual near real-time data propagation. The architecture takes full advantage of existing J2EE (Java 2 Platform, Enterprise Edition) technology and enables the implementation of a distributed, scalable, near real-time ETL environment. Instead of using vendor proprietary ETL (extraction, transformation, loading) solutions, which are often hard to scale and often do not support an optimization of allocated time frames for data extracts, we propose in our approach ETLets (spoken “et-lets”) and Enterprise Java Beans (EJB) for the ETL processing tasks. 1
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