8,238 research outputs found
Influence of magnetic viscosity on domain wall dynamics under spin-polarized currents
We present a theoretical study of the influence of magnetic viscosity on
current-driven domain wall dynamics. In particular we examine how domain wall
depinning transitions, driven by thermal activation, are influenced by the
adiabatic and nonadiabatic spin-torques. We find the Arrhenius law that
describes the transition rate for activation over a single energy barrier
remains applicable under currents but with a current-dependent barrier height.
We show that the effective energy barrier is dominated by a linear current
dependence under usual experimental conditions, with a variation that depends
only on the nonadiabatic spin torque coefficient beta.Comment: 8 pages, 4 figure
Local Hall effect in hybrid ferromagnetic/semiconductor devices
We have investigated the magnetoresistance of ferromagnet-semiconductor
devices in an InAs two-dimensional electron gas system in which the magnetic
field has a sinusoidal profile. The magnetoresistance of our device is large.
The longitudinal resistance has an additional contribution which is odd in
applied magnetic field. It becomes even negative at low temperature where the
transport is ballistic. Based on the numerical analysis, we confirmed that our
data can be explained in terms of the local Hall effect due to the profile of
negative and positive field regions. This device may be useful for future
spintronic applications.Comment: 4 pages with 4 fugures. Accepted for publication in Applied Physics
Letter
Temperature dependence of nonlinear auto-oscillator linewidths: Application to spin-torque nano-oscillators
The temperature dependence of the generation linewidth for an auto-oscillator
with a nonlinear frequency shift is calculated. It is shown that the frequency
nonlinearity creates a finite correlation time, tau, for the phase
fluctuations. In the low-temperature limit in which the spectral linewidth is
smaller than 1/tau, the line shape is approximately Lorentzian and the
linewidth is linear in temperature. In the opposite high-temperature limit in
which the linewidth is larger than 1/tau, the nonlinearity leads to an apparent
"inhomogeneous broadening" of the line, which becomes Gaussian in shape and has
a square-root dependence on temperature. The results are illustrated for the
spin-torque nano-oscillator.Comment: 4 pages, 1 figur
Locally Adaptive Products for Genuine Spherical Harmonic Lighting
Precomputed radiance transfer techniques have been broadly used for supporting complex illumination effects
on diffuse and glossy objects. Although working with the wavelet domain is efficient in handling all-frequency
illumination, the spherical harmonics domain is more convenient for interactively changing lights and views on
the fly due to the rotational invariant nature of the spherical harmonic domain. For interactive lighting, however,
the number of coefficients must be limited and the high orders of coefficients have to be eliminated. Therefore
spherical harmonic lighting has been preferred and practiced only for interactive soft-diffuse lighting. In this
paper, we propose a simple but practical filtering solution using locally adaptive products of high-order harmonic
coefficients within the genuine spherical harmonic lighting framework. Our approach works out on the fly in two
folds. We first conduct multi-level filtering on vertices in order to determine regions of interests, where the high
orders of harmonics are necessary for high frequency lighting. The initially determined regions of interests are
then refined through filling in the incomplete regions by traveling the neighboring vertices. Even not relying on
graphics hardware, the proposed method allows to compute high order products of spherical harmonic lighting for
both diffuse and specular lighting
Lattice paramenter, lattice disorder and resistivity of carbohydrate doepd MgB2 and their correlation with the transition temperature
The change in the lattice parameters or the lattice disorder is claimed as a
cause of the slight reduction in the transition temperature by carbon doping in
MgB2. In this work, an extensive investigation on the effects of carbohydrate
doping has been carried out. It is found that not only the a-axis but also the
c-axis lattice parameter increases with the sintering temperature. A linear
relation between the unit cell volume and the critical temperature is observed.
Compared with the well known correlation between the lattice strain and the
critical temperature, the X-ray peak broadening itself shows a closer
correlation with the transition temperature. The residual resistivity and the
critical temperature are linearly correlated with each other as well and its
implication is further discussed.Comment: 3 pages. Accepted by Jouranl of nanoscience and Nanotechnology (JNN
Lineshape distortion in a nonlinear auto-oscillator near generation threshold: Application to spin-torque nano-oscillators
The lineshape in an auto-oscillator with a large nonlinear frequency shift in
the presence of thermal noise is calculated. Near the generation threshold,
this lineshape becomes strongly non-Lorentzian, broadened, and asymmetric. A
Lorentzian lineshape is recovered far below and far above threshold, which
suggests that lineshape distortions provide a signature of the generation
threshold. The theory developed adequately describes the observed behavior of a
strongly nonlinear spin-torque nano-oscillator.Comment: 4 pages, 3 figure
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