93 research outputs found
Spin Dependent Tunneling in FM|semiconductor|FM structures
Here we show that ordinary band structure codes can be used to understand the
mechanisms of coherent spin-injection at interfaces between ferromagnets and
semiconductors. This approach allows the screening of different material
combinations for properties useful for obtaining high tunneling
magnetoresistance (TMR). We used the Vienna Ab-initio Simulation Code (VASP) to
calculate the wave function character of each band in periodic epitaxial
Fe(100)|GaAs(100) and Fe(100)|ZnSe(100) structures. It is shown that Fe wave
functions of different symmetry near Fermi energy decay differently in the GaAs
and ZnSe.Comment: Accepted for publication in MMM'05 Proceedings. 7 pages, 5 figure
Impurity induced enhancement of perpendicular magnetic anisotropy in Fe/MgO tunnel junctions
Using first-principles calculations, we investigated the impact of chromium
(Cr) and vanadium (V) impurities on the magnetic anisotropy and spin
polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated using
layer resolved anisotropy calculation technique, that while the impurity near
the interface has a drastic effect in decreasing the perpendicular magnetic
anisotropy (PMA), its position within the bulk allows maintaining high surface
PMA. Moreover, the effective magnetic anisotropy has a strong tendency to go
from in-plane to out-of-plane character as a function of Cr and V concentration
favoring out-of-plane magnetization direction for ~1.5 nm thick Fe layers at
impurity concentrations above 20 %. At the same time, spin polarization is not
affected and even enhanced in most situations favoring an increase of tunnel
magnetoresistance (TMR) values.Comment: 6 pages, 3 figure
Voltage induced control and magnetoresistance of noncollinear frustrated magnets
Noncollinear frustrated magnets are proposed as a new class of spintronic
materials with high magnetoresistance which can be controlled with relatively
small applied voltages. It is demonstrated that their magnetic configuration
strongly depends on position of the Fermi energy and applied voltage. The
voltage induced control of noncollinear frustrated materials (VCFM) can be seen
as a way to intrinsic control of colossal magnetoresistance (CMR) and is the
bulk material counterpart of spin transfer torque concept used to control giant
magnetoresistance in layered spin-valve structures.Comment: 4 pages, 4 figure
Anatomy of perpendicular magnetic anisotropy in Fe/MgO magnetic tunnel junctions: First principles insight
Using first-principles calculations, we elucidate microscopic mechanisms of
perpendicular magnetic anisotropy (PMA)in Fe/MgO magnetic tunnel junctions
through evaluation of orbital and layer resolved contributions into the total
anisotropy value. It is demonstrated that the origin of the large PMA values is
far beyond simply considering the hybridization between Fe-3dd_{yz(xz)}d_{z^2}d_{xy}d_{x^2-y^2}^2$.Comment: 5 pages, 5 figure
Intrinsic spin orbit torque in a single domain nanomagnet
We present theoretical studies of the intrinsic spin orbit torque (SOT) in a
single domain ferromagnetic layer with Rashba spin-orbit coupling (SOC) using
the non-equilibrium Green's function formalism for a model Hamiltonian. We find
that, to the first order in SOC, the intrinsic SOT has only the field-like
torque symmetry and can be interpreted as the longitudinal spin current induced
by the charge current and Rashba field. We analyze the results in terms of the
material related parameters of the electronic structure, such as band filling,
band width, exchange splitting, as well as the Rashba SOC strength. On the
basis of these numerical and analytical results, we discuss the magnitude and
sign of SOT. Our results show that the different sign of SOT in identical
ferromagnetic layers with different supporting layers, e.g. Co/Pt and Co/Ta,
could be attributed to electrostatic doping of the ferromagnetic layer by the
support.Comment: 10 pages, 2 figure
Magnetic Insulator-Induced Proximity Effects in Graphene: Spin Filtering and Exchange Splitting Gaps
We report on first-principles calculations of spin-dependent properties in
graphene induced by its interaction with a nearby magnetic insulator (Europium
oxide, EuO). The magnetic proximity effect results in spin polarization of
graphene orbitals by up to 24 %, together with large exchange splitting
bandgap of about 36 meV. The position of the Dirac cone is further shown to
depend strongly on the graphene-EuO interlayer. These findings point towards
the possible engineering of spin gating by proximity effect at relatively high
temperature, which stands as a hallmark for future all-spin information
processing technologies.Comment: 5 pages, 4 figure
Respective influence of in-plane and out-of-plane spin-transfer torques in magnetization switching of perpendicular magnetic tunnel junctions
The relative contributions of in-plane (damping-like) and out-of-plane
(field-like) spin-transfer-torques in the magnetization switching of
out-of-plane magnetized magnetic tunnel junctions (pMTJ) has been theoretically
analyzed using the transformed Landau-Lifshitz (LL) equation with the STT
terms. It is demonstrated that in a pMTJ structure obeying macrospin dynamics,
the out-of-plane torque influences the precession frequency but it does not
contribute significantly to the STT switching process (in particular to the
switching time and switching current density), which is mostly determined by
the in-plane STT contribution. This conclusion is confirmed by finite
temperature and finite writing pulse macrospin simulations of the current-field
switching diagrams. It contrasts with the case of STT-switching in in-plane
magnetized MTJ in which the field-like term also influences the switching
critical current. This theoretical analysis was successfully applied to the
interpretation of voltage-field STT switching diagrams experimentally measured
on perpendicular MTJ pillars 36 nm in diameter, which exhibit macrospin-like
behavior. The physical nonequivalence of Landau and Gilbert dissipation terms
in presence of STT-induced dynamics is also discussed
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