462 research outputs found
Switching the magnetic configuration of a spin valve by current induced domain wall motion
We present experimental results on the displacement of a domain wall by
injection of a dc current through the wall. The samples are 1 micron wide long
stripes of a CoO/Co/Cu/NiFe classical spin valve structure.
The stripes have been patterned by electron beam lithography. A neck has been
defined at 1/3 of the total length of the stripe and is a pinning center for
the domain walls, as shown by the steps of the giant magnetoresistance curves
at intermediate levels (1/3 or 2/3) between the resistances corresponding to
the parallel and antiparallel configurations. We show by electric transport
measurements that, once a wall is trapped, it can be moved by injecting a dc
current higher than a threshold current of the order of magnitude of 10^7
A/cm^2. We discuss the different possible origins of this effect, i.e. local
magnetic field created by the current and/or spin transfer from spin polarized
current.Comment: 3 pages, 3 figure
Switching a spin-valve back and forth by current-induced domain wall motion
We have studied the current-induced displacement of a domain wall (DW) in the
permalloy (Py) layer of a Co/Cu/Py spin valve structure at zero and very small
applied field. The displacement is in opposite direction for opposite dc
currents, and the current density required to move DW is only of the order of
10^6 A/cm^2. For H = 3 Oe, a back and forth DW motion between two stable
positions is observed. We also discuss the effect of an applied field on the DW
motion.Comment: 4 pages, 3 figure
Direct probing of band-structure Berry phase in diluted magnetic semiconductors
We report on experimental evidence of the Berry phase accumulated by the
charge carrier wave function in single-domain nanowires made from a
(Ga,Mn)(As,P) diluted ferromagnetic semiconductor layer. Its signature on the
mesoscopic transport measurements is revealed as unusual patterns in the
magnetoconductance, that are clearly distinguished from the universal
conductance fluctuations. We show that these patterns appear in a magnetic
field region where the magnetization rotates coherently and are related to a
change in the band-structure Berry phase as the magnetization direction
changes. They should be thus considered as a band structure Berry phase
fingerprint of the effective magnetic monopoles in the momentum space. We argue
that this is an efficient method to vary the band structure in a controlled way
and to probe it directly. Hence, (Ga,Mn)As appears to be a very interesting
test bench for new concepts based on this geometrical phase.Comment: 7 pages, 6 figure
Noise dephasing in the edge states of the Integer Quantum Hall regime
An electronic Mach Zehnder interferometer is used in the integer quantum hall
regime at filling factor 2, to study the dephasing of the interferences. This
is found to be induced by the electrical noise existing in the edge states
capacitively coupled to each others. Electrical shot noise created in one
channel leads to phase randomization in the other, which destroys the
interference pattern. These findings are extended to the dephasing induced by
thermal noise instead of shot noise: it explains the underlying mechanism
responsible for the finite temperature coherence time of the
edge states at filling factor 2, measured in a recent experiment. Finally, we
present here a theory of the dephasing based on Gaussian noise, which is found
in excellent agreement with our experimental results.Comment: ~4 pages, 4 figure
Tuning decoherence with a voltage probe
We present an experiment where we tune the decoherence in a quantum
interferometer using one of the simplest object available in the physic of
quantum conductors : an ohmic contact. For that purpose, we designed an
electronic Mach-Zehnder interferometer which has one of its two arms connected
to an ohmic contact through a quantum point contact. At low temperature, we
observe quantum interference patterns with a visibility up to 57%. Increasing
the connection between one arm of the interferometer to the floating ohmic
contact, the voltage probe, reduces quantum interferences as it probes the
electron trajectory. This unique experimental realization of a voltage probe
works as a trivial which-path detector whose efficiency can be simply tuned by
a gate voltage
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
Alterations of cardiovascular complexity during acute exposure to high altitude: A multiscale entropy approach
Stays at high altitude induce alterations in cardiovascular control and are a model of specific pathological cardiovascular derangements at sea level. However, high-altitude alterations of the complex cardiovascular dynamics remain an almost unexplored issue. Therefore, our aim is to describe the altered cardiovascular complexity at high altitude with a multiscale entropy (MSE) approach. We recorded the beat-by-beat series of systolic and diastolic blood pressure and heart rate in 20 participants for 15 min twice, at sea level and after arrival at 4554 m a.s.l. We estimated Sample Entropy and MSE at scales of up to 64 beats, deriving average MSE values over the scales corresponding to the high-frequency (MSEHF) and low-frequency (MSELF) bands of heart-rate variability. We found a significant loss of complexity at heart-rate and blood-pressure scales complementary to each other, with the decrease with high altitude being concentrated at Sample Entropy and at MSEHF for heart rate and at MSELF for blood pressure. These changes can be ascribed to the acutely increased chemoreflex sensitivity in hypoxia that causes sympathetic activation and hyperventilation. Considering high altitude as a model of pathological states like heart failure, our results suggest new ways for monitoring treatments and rehabilitation protocols
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