1,133 research outputs found
Circuit model for spin-bottleneck resistance in magnetic-tunnel-junction devices
Spin-bottlenecks are created in magnetic-tunnel-junction devices by spatial
inhomogeneity in the relative resistances for up and down spins. We propose a
simple electrical circuit model for these devices which incorporates
spin-bottleneck effects and can be used to calculate their overall resistance
and magnetoresistance. The model permits a simple understanding of the
dependence of device magnetoresistance on spin diffusion lengths, tunneling
magnetoresistance, and majority and minority spin resistivities in the
ferromagnetic electrodes. The circuit model is in a good quantitative agreement
with detailed transport calculations.Comment: 4 pages, 3 figures, submitted to Phys. Rev.
Theory of Weak Localization in Ferromagnetic (Ga,Mn)As
We study quantum interference corrections to the conductivity in (Ga,Mn)As
ferromagnetic semiconductors using a model with disordered valence band holes
coupled to localized Mn moments through a p-d kinetic-exchange interaction. We
find that at Mn concentrations above 1% quantum interference corrections lead
to negative magnetoresistance, i.e. to weak localization (WL) rather than weak
antilocalization (WAL). Our work highlights key qualitative differences between
(Ga,Mn)As and previously studied toy model systems, and pinpoints the mechanism
by which exchange splitting in the ferromagnetic state converts valence band
WAL into WL. We comment on recent experimental studies and theoretical analyses
of low-temperature magnetoresistance in (Ga,Mn)As which have been variously
interpreted as implying both WL and WAL and as requiring an impurity-band
interpretation of transport in metallic (Ga,Mn)As.Comment: 16 pages, 10 figures; submitted to Phys. Rev.
Non-vanishing spin Hall currents in disordered spin-orbit coupling systems
Spin currents that flow perpendicular to the electric field direction are
generic in metals and doped semiconductors with spin-orbit coupling. It has
recently been argued that the spin Hall conductivity can be dominated by an
intrinsic contribution which follows from Bloch state distortion in the
presence of an electric field. Here we report on an numerical demonstration of
the robustness of this effect in the presence of disorder scattering for the
case of a two-dimensional electron-gas with Rashba spin-orbit interactions
(R2DES).Comment: 4 pages, 3 figure
Boltzmann theory of engineered anisotropic magnetoresistance in (Ga,Mn)As
We report on a theoretical study of dc transport coefficients in (Ga,Mn)As
diluted magnetic semiconductor ferromagnets that accounts for quasiparticle
scattering from ionized Mn acceptors with a local moment and
from non-magnetic compensating defects. In metallic samples Boltzmann transport
theory with Golden rule scattering rates accounts for the principle trends of
the measured difference between resistances for magnetizations parallel and
perpendicular to the current. We predict that the sign and magnitude of the
anisotropic magnetoresistance can be changed by strain engineering or by
altering chemical composition.Comment: 4 pages, 2 figure
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