941 research outputs found
Synchronization of spin-transfer oscillators driven by stimulated microwave currents
We have simulated the non-linear dynamics of networks of spin-transfer
oscillators. The oscillators are magnetically uncoupled but electrically
connected in series. We use a modified Landau-Lifschitz- Gilbert equation to
describe the motion of each oscillator in the presence of the oscillations of
all the others. We show that the oscillators of the network can be synchronized
not only in frequency but also in phase. The coupling is due to the microwave
components of the current induced in each oscillator by the oscillations in all
the other oscillators. Our results show how the emitted microwave power of
spin-transfer oscillators can be considerably enhanced by current-induced
synchronization in an electrically connected network. We also discuss the
possible application of our synchronization mechanism to the interpretation of
the surprisingly narrow microwave spectrum in some isolated spin-transfer
oscillators
Anomalous Hall Effect in Ferromagnetic Metals: Role of Phonons at Finite Temperature
The anomalous Hall effect in a multiband tight-binding model is numerically
studied taking into account both elastic scattering by disorder and inelastic
scattering by the electron-phonon interaction. The Hall conductivity is
obtained as a function of temperature , inelastic scattering rate ,
chemical potential , and impurity concentration . We find
that the new scaling law holds over a wide range of these parameters;
, with () being the
conductivity tensor (with only elastic scattering), which corresponds to the
recent experimental observation [Phys. Rev. Lett. {\bf 103} (2009) 087206]. The
condition of this scaling is examined. Also, it is found that the intrinsic
mechanism depends on temperature under a resonance condition.Comment: 5 figure
Enhancement of the Spin Accumulation at the Interface Between a Spin-Polarized Tunnel Junction and a Semiconductor
We report on spin injection experiments at a Co/AlO/GaAs interface
with electrical detection. The application of a transverse magnetic field
induces a large voltage drop at the interface as high as 1.2mV for a
current density of 0.34 nA.. This represents a dramatic increase of
the spin accumulation signal, well above the theoretical predictions for spin
injection through a ferromagnet/semiconductor interface. Such an enhancement is
consistent with a sequential tunneling process via localized states located in
the vicinity of the AlO/GaAs interface. For spin-polarized carriers
these states act as an accumulation layer where the spin lifetime is large. A
model taking into account the spin lifetime and the escape tunneling time for
carriers travelling back into the ferromagnetic contact reproduces accurately
the experimental results
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
Anisotropic magneto-Coulomb effect versus spin accumulation in a ferromagnetic single-electron device
We investigate the magneto-transport characteristics of nanospintronics
single-electron devices. The devices consist of single non-magnetic
nano-objects (nanometer size nanoparticles of Al or Cu) connected to Co
ferromagnetic leads. The comparison with simulations allows us attribute the
observed magnetoresistance to either spin accumulation or anisotropic
magneto-Coulomb effect (AMC), two effects with very different origins. The fact
that the two effects are observed in similar samples demonstrates that a
careful analysis of Coulomb blockade and magnetoresistance behaviors is
necessary in order to discriminate them in magnetic single-electron devices. As
a tool for further studies, we propose a simple way to determine if spin
transport or AMC effect dominates from the Coulomb blockade I-V curves of the
spintronics device
Ordering in a spin glass under applied magnetic field
Torque, torque relaxation, and magnetization measurements on a AuFe spin
glass sample are reported. The experiments carried out up to 7 T show a
transverse irreversibility line in the (H,T) plane up to high applied fields,
and a distinct strong longitudinal irreversibility line at lower fields. The
data demonstrate for that this type of sample, a Heisenberg spin glass with
moderately strong anisotropy, the spin glass ordered state survives under high
applied fields in contrast to predictions of certain "droplet" type scaling
models. The overall phase diagram closely ressembles those of mean field or
chiral models, which both have replica symmetry breaking transitions.Comment: 4 pages, 3 figures, accepted for PR
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
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