2,690 research outputs found
Nonlinear spin dynamics of ferromagnetic ring in the vortex state and its application for spin-transfer nano-oscillator
We study a nonlinear spin dynamics of a ferromagnetic ring in a vortex state
induced by the spin-polarized current. We also suggest to use the ferromagnetic
ring as a free layer of a coreless vortex spin-transfer nano-oscillator. The
calculated working frequency is about several GHz, that is much higher than the
gyromode frequency of the disk-based vortex oscillator. The response of the
vortex-state ring to the spin-polarized current has hysteretic behavior with
the reasonable values of the thresholds current densities: ignition threshold
is about , and elimination current to maintain
the oscillations has much lower values about .
The output signal can be extracted by the help of the inverse spin Hall effect
or by the giant magnetoresistance. The output electromotive force averaged over
all sample vanishes, and we suggest to use a ferromagnetic ring or disk in a
vortex state as a GMR analyzer. For an inverse spin Hall analyser we advise to
use two heavy metals with different signs of Spin-Hall angle. The ring-based
STNO is supposed to increase the areas of practical application of the STNOs.Comment: 15 pages, 8 figure
Impurity center in a semiconductor quantum ring in the presence of a radial electric field
The problem of an impurity electron in a quantum ring (QR) in the presence of
a radially directed strong external electric field is investigated in detail.
Both an analytical and a numerical approach to the problem are developed. The
analytical investigation focuses on the regime of a strong wire-electric field
compared to the electric field due to the impurity. An adiabatic and
quasiclassical approximation is employed. The explicit dependencies of the
binding energy of the impurity electron on the electric field strength,
parameters of the QR and position of the impurity within the QR are obtained.
Numerical calculations of the binding energy based on a finite-difference
method in two and three dimensions are performed for arbitrary strengths of the
electric field. It is shown that the binding energy of the impurity electron
exhibits a maximum as a function of the radial position of the impurity that
can be shifted arbitrarily by applying a corresponding wire-electric field. The
maximal binding energy monotonically increases with increasing electric field
strength. The inversion effect of the electric field is found to occur. An
increase of the longitudinal displacement of the impurity typically leads to a
decrease of the binding energy. Results for both low- and high-quantum rings
are derived and discussed. Suggestions for an experimentally accessible set-up
associated with the GaAs/GaAlAs QR are provided.Comment: 16 pages, 8 figure
Auxiliary tensor fields for Sp(2,R) self-duality
The coset Sp(2,R)/U(1) is parametrized by two real scalar fields. We
generalize the formalism of auxiliary tensor (bispinor) fields in U(1)
self-dual nonlinear models of abelian gauge fields to the case of Sp(2,R)
self-duality. In this new formulation, Sp(2,R) duality of the nonlinear
scalar-gauge equations of motion is equivalent to an Sp(2,R) invariance of the
auxiliary interaction. We derive this result in two different ways, aiming at
its further application to supersymmetric theories. We also consider an
extension to interactions with higher derivatives.Comment: 1 + 24 page
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