710 research outputs found
Effect of Spin-Flip Scattering on Electrical Transport in Magnetic Tunnel Junctions
By means of the nonequilibrium Green function technique, the effect of
spin-flip scatterings on the spin-dependent electrical transport in
ferromagnet-insulator-ferromagnet (FM-I-FM) tunnel junctions is investigated.
It is shown that Julliere's formula for the tunnel conductance must be modified
when including the contribution from the spin-flip scatterings. It is found
that the spin-flip scatterings could lead to an angular shift of the tunnel
conductance, giving rise to the junction resistance not being the largest when
the orientations of magnetizations in the two FM electrodes are antiparallel,
which may offer an alternative explanation for such a phenomenon observed
previously in experiments in some FM-I-FM junctions. The spin-flip assisted
tunneling is also observed.Comment: Revtex, 4 figure
Spin-polarized tunneling through a thin-film
The effect of spin-disorder scattering on perpendicular transport in a
magnetic monolayer is considered within the single-site Coherent Potential
Approximation (CPA). The exchange interaction between a conduction electron and
localized moment of the magnetic ion is treated with the use of the
model. Electron-spin polarization is evaluated in the tunnel current which
comes from the different densities of spin-up, spin-down conduction electrons
at the Fermi level in a ferromagnetic semiconductor (EuS). Calculated results
are compared with some tunneling experiments.Comment: 5 pages, LaTex, 2 EPS figure
Magnetoresistance of Granular Ferromagnets - Observation of a Magnetic Proximity Effect?
We have observed a superparamagnetic to ferromagnetic transition in films of
isolated Ni grains covered by non-magnetic overlayers. The magnetoresistance
(MR) of the films was measured as a function of the overlayer thickness.
Initially, the granular Ni films exhibited negative MR curves peaked at H=0. As
different materials were deposited onto the grains hysteresis developed in the
MR. This behavior is ascribed to an increase of the typical domain size due to
magnetic coupling between grains. The strength of the inter-grain coupling is
found to correlate with the magnetic susceptibility of the overlayer material.
We discuss possible mechanisms for this coupling and suggest that the data may
reflect the existence of a magnetic proximity effect (analogous to the
well-known effect in superconductivity) in which a ferromagnetic moment is
induced in the metallic non-magnetic medium.Comment: 4 pages, 5 figure
Spin-filtered Edge States with an Electrically Tunable Gap in a Two-Dimensional Topological Crystalline Insulator
Three-dimensional topological crystalline insulators were recently predicted
and observed in the SnTe class of IV-VI semiconductors, which host metallic
surface states protected by crystal symmetries. In this work, we study thin
films of these materials and expose their potential for device applications. We
demonstrate that thin films of SnTe and Pb(1-x)Sn(x)Se(Te) grown along the
(001) direction are topologically nontrivial in a wide range of film thickness
and carry conducting spin-filtered edge states that are protected by the (001)
mirror symmetry via a topological invariant. Application of an electric field
perpendicular to the film will break the mirror symmetry and generate a band
gap in these edge states. This functionality motivates us to propose a novel
topological transistor device, in which charge and spin transport are maximally
entangled and simultaneously controlled by an electric field. The high on/off
operation speed and coupling of spin and charge in such a device may lead to
electronic and spintronic applications for topological crystalline insulators.Comment: 6 pages, 5 figures, minor changes made, accepted to Nature Material
Spin-dependent resonant tunneling in ZnSe/ZnMnSe heterostructures
Using the transfer matrix method and the effective-mass approximation, the
effect of resonant states on spin transport is studied in
ZnSe/ZnMnSe/ZnSe/ZnMnSe/ZnSe structures under the influence of both electric
and magnetic fields. The numerical results show that the ZnMnSe layers, which
act as spin filters, polarize the electric currents. Variation of thickness of
the central ZnSe layer shifts the resonant levels and exhibits an oscillatory
behavior in spin current densities. It is also shown that the spin polarization
of the tunneling current in geometrical asymmetry of the heterostructure where
two ZnMnSe layers have different Mn concentrations, depends strongly on the
thickness and the applied bias.Comment: 13 pages, 6 figure
Canted Magnetization Texture in Ferromagnetic Tunnel Junctions
We study the formation of inhomogeneous magnetization texture in the vicinity
of a tunnel junction between two ferromagnetic wires nominally in the
antiparallel configuration and its influence on the magnetoresistance of such a
device. The texture, dependent on magnetization rigidity and crystalline
anisotropy energy in the ferromagnet, appears upon an increase of ferromagnetic
inter-wire coupling above a critical value and it varies with an external
magnetic field.Comment: 5 pages, 4 figure
Electronic Phase Separation in Manganite/Insulator Interfaces
By using a realist microscopic model, we study the electric and magnetic
properties of the interface between a half metallic manganite and an insulator.
We find that the lack of carriers at the interface debilitates the double
exchange mechanism, weakening the ferromagnetic coupling between the Mn ions.
In this situation the ferromagnetic order of the Mn spins near the interface is
unstable against antiferromagnetic CE correlations, and a separation between
ferromagnetic/metallic and antiferromagnetic/insulator phases at the interfaces
can occur. We obtain that the insertion of extra layers of undoped manganite at
the interface introduces extra carriers which reinforce the double exchange
mechanism and suppress antiferromagnetic instabilities.Comment: 8 pages, 7 figures include
Progress and prospects in the quantum anomalous Hall effect
The quantum anomalous Hall effect refers to the quantization of Hall effect
in the absence of applied magnetic field. The quantum anomalous Hall effect is
of topological nature and well suited for field-free resistance metrology and
low-power information processing utilizing dissipationless chiral edge
transport. In this Perspective, we provide an overview of the recent
achievements as well as the materials challenges and opportunities, pertaining
to engineering intrinsic/interfacial magnetic coupling, that are expected to
propel future development of the field.Comment: Invited for APL Materials, Special Topic - Materials Challenges and
Synthesis Science of Emerging Quantum Material
A superconducting absolute spin valve
A superconductor with a spin-split excitation spectrum behaves as an ideal
ferromagnetic spin-injector in a tunneling junction. It was theoretical
predicted that the combination of two such spin-split superconductors with
independently tunable magnetizations, may be used as an ideal
spin-valve. Here we report on the first switchable superconducting spin-valve
based on two EuS/Al bilayers coupled through an aluminum oxide tunnel barrier.
The spin-valve shows a relative resistance change between the parallel and
antiparallel configuration of the EuS layers up to 900% that demonstrates a
highly spin-polarized currents through the junction. Our device may be pivotal
for realization of thermoelectric radiation detectors, logical element for a
memory cell in cryogenics superconductor-based computers and superconducting
spintronics in general.Comment: 6 pages, 4 color figures, 1 tabl
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