1,259 research outputs found
Spin motive forces and current fluctuations due to Brownian motion of domain walls
We compute the power spectrum of the noise in the current due to spin motive
forces by a fluctuating domain wall. We find that the power spectrum of the
noise in the current is colored, and depends on the Gilbert damping, the spin
transfer torque parameter , and the domain-wall pinning potential and
magnetic anisotropy. We also determine the average current induced by the
thermally-assisted motion of a domain wall that is driven by an external
magnetic field. Our results suggest that measuring the power spectrum of the
noise in the current in the presence of a domain wall may provide a new method
for characterizing the current-to-domain-wall coupling in the system.Comment: Submitted to "Special issue: Caloritronics" in Solid State
Communication
Spin-transfer mechanism for magnon-drag thermopower
We point out a relation between the dissipative spin-transfer-torque
parameter and the contribution of magnon drag to the thermoelectric
power in conducting ferromagnets. Using this result we estimate in iron
at low temperatures, where magnon drag is believed to be the dominant
contribution to the thermopower. Our results may be used to determine
from magnon-drag-thermopower experiments, or, conversely, to infer the strength
of magnon drag via experiments on spin transfer
Non-resonant background suppression in preresonance CARS spectra of flavin adenine dinucleotide: Demonstration of a background suppression technique using phase mismatching and comparison with the polarization-sensitive CARS technique
Polarization-sensitive CARS spectra of a 5.7 × 10-3 mol dm-3 flavin adenine dinucleotide (FAD) solution were recorded under preresonance conditions at a pump wavelength of 532 nm. The depolarization ratios of the vibrations are shown to be close to the depolarization ratio of the non-resonant background. This results in a severe reduction of the vibration resonant signal (a factor of 700-900) in the polarization CARS spectrum, and a poor improvement in the ratio of the resonant signal and the non-resonant background (<10). \ud
In this context, a non-resonant background suppression technique is discussed and demonstrated for 5.7 × 10-3 and 1.4 × 10-3 mol dm-3 FAD solutions excited at 532 nm; the non-resonant susceptibility of the walls of the cuvette, which contains the FAD solution, is used to compensate the non-resonant signal contribution of the solution. An improvement in the signal-to-noise ratio of ca. 50 is achieved at the cost of a factor of 30 in the resonant signal strength. Lorentzian-shaped spectral bands are obtained, facilitating the determination of band position, width and intensity. Line shape parameters and depolarization ratios for FAD are extracted from the presented spectra by curve fitting. The signal strength and background suppression achieved with these techniques and the resonance CARS technique (at a pump wavelength of 480 nm) are compared and discussed
Current-driven and field-driven domain walls at nonzero temperature
We present a model for the dynamics of current- and field-driven domain-wall
lines at nonzero temperature. We compute thermally-averaged drift velocities
from the Fokker-Planck equation that describes the nonzero-temperature dynamics
of the domain wall. As special limits of this general description, we describe
rigid domain walls as well as vortex domain walls. In these limits, we
determine also depinning times of the domain wall from an extrinsic pinning
potential. We compare our theory with previous theoretical and experimental
work
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Spin motive forces due to magnetic vortices and domain walls
We study spin motive forces, i.e, spin-dependent forces, and voltages induced
by time-dependent magnetization textures, for moving magnetic vortices and
domain walls. First, we consider the voltage generated by a one-dimensional
field-driven domain wall. Next, we perform detailed calculations on
field-driven vortex domain walls. We find that the results for the voltage as a
function of magnetic field differ between the one-dimensional and vortex domain
wall. For the experimentally relevant case of a vortex domain wall, the
dependence of voltage on field around Walker breakdown depends qualitatively on
the ratio of the so-called -parameter to the Gilbert damping constant,
and thus provides a way to determine this ratio experimentally. We also
consider vortices on a magnetic disk in the presence of an AC magnetic field.
In this case, the phase difference between field and voltage on the edge is
determined by the parameter, providing another experimental method to
determine this quantity.Comment: 8 pages, 9 figures, submitted to PR
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Current-induced spin torques in III-V ferromagnetic semiconductors
We formulate a theory of current-induced spin torques in inhomogeneous III-V
ferromagnetic semiconductors. The carrier spin-3/2 and large spin-orbit
interaction, leading to spin non-conservation, introduce significant conceptual
differences from spin torques in ferromagnetic metals. We determine the spin
density in an electric field in the weak momentum scattering regime,
demonstrating that the torque on the magnetization is intimately related to
spin precession under the action of both the spin-orbit interaction and the
exchange field characteristic of ferromagnetism. The spin polarization excited
by the electric field is smaller than in ferromagnetic metals and, due to lack
of angular momentum conservation, cannot be expressed in a simple closed
vectorial form. Remarkably, scalar and spin-dependent scattering do not affect
the result. We use our results to estimate the velocity of current-driven
domain walls.Comment: 10 page
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