284 research outputs found
Frequency modulation of spin torque oscillator pairs
The current controlled modulation of nano-contact based spin torque
oscillator (STO) pairs is studied in both the synchronized and non-synchronized
states. The synchronized state shows a well behaved modulation and demonstrates
robust mutual locking even under strong modulation. The power distribution of
the modulation sidebands can be quantitatively described by assuming a single
oscillator model. However, in the non-synchronized state, the modulation
sidebands are not well described by the model, indicating interactions between
the two individual nano-contact STOs. These findings are promising for
potential applications requiring the modulation of large synchronized STO
arrays
Non-linear frequency and amplitude modulation of a nano-contact spin torque oscillator
We study the current controlled modulation of a nano-contact spin torque
oscillator. Three principally different cases of frequency non-linearity
( being zero, positive, and negative) are investigated.
Standard non-linear frequency modulation theory is able to accurately describe
the frequency shifts during modulation. However, the power of the modulated
sidebands only agrees with calculations based on a recent theory of combined
non-linear frequency and amplitude modulation.Comment: 4 pages, 4 figure
Bias dependence of perpendicular spin torque and of free and fixed layer eigenmodes in MgO-based nanopillars
We have measured the bias voltage and field dependence of eigenmode
frequencies in a magnetic tunnel junction with MgO barrier. We show that both
free layer (FL) and reference layer (RL) modes are excited, and that a
cross-over between these modes is observed by varying external field and bias
voltage. The bias voltage dependence of the FL and RL modes are shown to be
dramatically different. The bias dependence of the FL modes is linear in bias
voltage, whereas that of the RL mode is strongly quadratic. Using modeling and
micromagnetic simulations, we show that the linear bias dependence of FL
frequencies is primarily due to a linear dependence of the perpendicular spin
torque on bias voltage, whereas the quadratic dependence of the RL on bias
voltage is dominated by the reduction of exchange bias due to Joule heating,
and is not attributable to a quadratic dependence of the perpendicular spin
torque on bias voltage
Temperature dependence of linewidth in nano-contact based spin torque oscillators: effect of multiple oscillatory modes
We discuss the effect of mode transitions on the current (I) and temperature
(T) dependent linewidth (\Delta f) in nanocontact based spin torque oscillators
(STOs). At constant I, \Delta f exhibits an anomalous temperature dependence
near the mode transitions; \Delta f may either increase or decrease with T
depending on the position w.r.t. the mode transition. We show that the behavior
of \Delta f as a function of I can be fitted by the single mode analytical
theory of STOs, even though there are two modes present near the mode
transition, if the nonlinear amplification is determined directly from the
experiment. Using a recently developed theory of two coupled modes, we show
that the linewidth near mode transition can be described by an "effective"
single-oscillator theory with an enhanced nonlinear amplification that carries
additional temperature dependence, which thus qualitatively explain the
experimental results.Comment: 8 page
Dynamic Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions
Precisely engineered tunnel junctions exhibit a long sought effect that
occurs when the energy of the electron is comparable to the potential energy of
the tunneling barrier. The resistance of metal-insulator-metal tunnel junctions
oscillates with an applied voltage when electrons that tunnel directly into the
barrier's conduction band interfere upon reflection at the classical turning
points: the insulator-metal interface, and the dynamic point where the incident
electron energy equals the potential barrier inside the insulator. A model of
tunneling between free electron bands using the exact solution of the
Schroedinger equation for a trapezoidal tunnel barrier qualitatively agrees
with experiment.Comment: 4pgs, 3 fig
Lighting Recommendations in Operating Theatres
“The eyes lead the body.” A good visual environment is important for performance and wellbeing. Unsatisfactory visual conditions often induce a strained posture, more or less unconsciously, in an effort to improve vision. The requirements for the visual environment in an operating theatre are high. Surgeons or assistants who are having visual problems can induce treatment hazards. The purpose of this study was to evaluate the visual environment in operating theatres, and also examine if the surgeon’s visual acuity at near work can be improved with better glasses. Thirty percent of the surgeons had eyestrain, and those with eyestrain had three times as much musculoskeletal strain. The measurements of the illuminance and luminance show a low uniformity level on the operating table; the operating lamps give an average of 100.000 lux, while the surrounding area values are much lower. The most important recommendation for lighting intervention in the operating theatre is a more uniform illuminance on the operating table
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