259 research outputs found
Spin Injection in Quantum Wells with Spatially Dependent Rashba Interaction
We consider Rashba spin-orbit effects on spin transport driven by an electric
field in semiconductor quantum wells. We derive spin diffusion equations that
are valid when the mean free path and the Rashba spin-orbit interaction vary on
length scales larger than the mean free path in the weak spin-orbit coupling
limit. From these general diffusion equations, we derive boundary conditions
between regions of different spin-orbit couplings. We show that spin injection
is feasible when the electric field is perpendicular to the boundary between
two regions. When the electric field is parallel to the boundary, spin
injection only occurs when the mean free path changes within the boundary, in
agreement with the recent work by Tserkovnyak et al. [cond-mat/0610190].Comment: 7 pages, 1 figur
Conditions for extreme sensitivity of protein diffusion in membranes to cell environments
We study protein diffusion in multicomponent lipid membranes close to a rigid
substrate separated by a layer of viscous fluid. The large-distance, long-time
asymptotics for Brownian motion are calculated using a nonlinear stochastic
Navier-Stokes equation including the effect of friction with the substrate. The
advective nonlinearity, neglected in previous treatments, gives only a small
correction to the renormalized viscosity and diffusion coefficient at room
temperature. We find, however, that in realistic multicomponent lipid mixtures,
close to a critical point for phase separation, protein diffusion acquires a
strong power-law dependence on temperature and the distance to the substrate
, making it much more sensitive to cell environment, unlike the logarithmic
dependence on and very small thermal correction away from the critical
point.Comment: 19 pages, 4 figure
Microwave response of a magnetic single-electron transistor
We consider a single-electron transistor in the form of a ferromagnetic dot
in contact with normal-metal and pinned ferromagnetic leads. Microwave-driven
precession by the dot induces a pumped electric current. In open circuits, this
pumping produces a measurable reverse bias voltage, which can be enhanced and
made highly nonlinear by Coulomb blockade in the dot. The dependence of this
bias on the power and spectrum of microwave irradiation may be utilized to
develop nanoscale microwave detectors analogous to single-electron
transistor-based electrostatic sensors and nanoelectromechanical devices.Comment: 5 pages, 4 figure
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
First-principles study of magnetization relaxation enhancement and spin-transfer in thin magnetic films
The interface-induced magnetization damping of thin ferromagnetic films in
contact with normal-metal layers is calculated from first principles for clean
and disordered Fe/Au and Co/Cu interfaces. Interference effects arising from
coherent scattering turn out to be very small, consistent with a very small
magnetic coherence length. Because the mixing conductances which govern the
spin transfer are to a good approximation real valued, the spin pumping can be
described by an increased Gilbert damping factor but an unmodified gyromagnetic
ratio. The results also confirm that the spin-current induced magnetization
torque is an interface effect.Comment: 10 pages, 8 figures, RevTeX; modified according to Referees' request
Nonlocal magnetization dynamics in ferromagnetic heterostructures
Two complementary effects modify the GHz magnetization dynamics of nanoscale
heterostructures of ferromagnetic and normal materials relative to those of the
isolated magnetic constituents: On the one hand, a time-dependent ferromagnetic
magnetization pumps a spin angular-momentum flow into adjacent materials and,
on the other hand, spin angular momentum is transferred between ferromagnets by
an applied bias, causing mutual torques on the magnetizations. These phenomena
are manifestly nonlocal: they are governed by the entire spin-coherent region
that is limited in size by spin-flip relaxation processes. We review recent
progress in understanding the magnetization dynamics in ferromagnetic
heterostructures from first principles, focusing on the role of spin pumping in
layered structures. The main body of the theory is semiclassical and based on a
mean-field Stoner or spin-density--functional picture, but quantum-size effects
and the role of electron-electron correlations are also discussed. A growing
number of experiments support the theoretical predictions. The formalism should
be useful to understand the physics and to engineer the characteristics of
small devices such as magnetic random-access memory elements.Comment: 48 pages, 21 figures (3 in color
Microscopic Calculation of Spin Torques in Disordered Ferromagnets
Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called -term and the Gilbert damping, , in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as
hold for localized as well as itinerant ferromagnetism.Comment: 4 page
- …