26 research outputs found
Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions
The bias dependence of the tunnel magnetoresistance (TMR) of Fe/MgO/Fe tunnel
junctions is investigated theoretically with a fully self-consistent scheme
that combines the non-equilibrium Green's functions method with density
functional theory. At voltages smaller than 20 mVolt the I-V characteristics
and the TMR are dominated by resonant transport through narrow interface states
in the minority spin-band. In the parallel configuration this contribution is
quenched by a voltage comparable to the energy width of the interface state,
whereas it persists at all voltages in the anti-parallel configuration. At
higher bias the transport is mainly determined by the relative positions of the
band-edges in the two Fe electrodes, which causes a decrease of the
TMR
Role of Coulomb correlation on magnetic and transport properties of doped manganites: La0.5Sr0.5MnO3 and LaSr2Mn2O7
Results of LSDA and LSDA+U calculations of the electronic structure and
magnetic configurations of the 50% hole-doped pseudocubic perovskite
La0.5Sr0.5MnO3 and double layered LaSr2Mn2O7 are presented. We demonstrate that
the on-site Coulomb correlation (U) of Mn d electrons has a very different
influence on the (i) band formations, (ii) magnetic ground states, (iii)
interlayer exchange interactions, and (iv) anisotropy of the electrical
transport in these two manganites. A possible reason why the LSDA failures in
predicting observed magnetic and transport properties of the double layered
compound - in contrast to the doped perovskite manganite - is considered on the
basis of a p-d hybridization analysis.Comment: 11 pages, 3 figure
Coulomb correlation and magnetic ordering in double-layered manganites: LaSrMnO
A detailed study of the electronic structure and magnetic configurations of
the 50 % hole-doped double layered manganite LaSrMnO is presented.
We demonstrate that the on-site Coulomb correlation (U) of Mn d electrons {\it
(i)} significantly modifies the electronic structure, magnetic ordering (from
FM to AFM), and interlayer exchange interactions, and {\it (ii)} promotes
strong anisotropy in electrical transport, reducing the effective hopping
parameter along the {\it c} axis for electrically active electrons. This
findng is consistent with observations of anisotropic transport -- a property
which sets this manganite apart from conventional 3D systems. A half-metallic
band structure is predicted with both the LSDA and LSDA+U methods. The
experimentally observed A-type AFM ordering in LaSrMnO is found to
be energetically more favorable with U 7 eV. A simple interpretation of
interlayer exchange coupling is given within double and super-exchange
mechanisms based on the dependencies on U of the effective exchange parameters
and state sub-band widths.Comment: 10 pages, 5 figure
Generalized stacking fault energetics and dislocation properties: compact vs. spread unit dislocation structures in TiAl and CuAu
We present a general scheme for analyzing the structure and mobility of
dislocations based on solutions of the Peierls-Nabarro model with a two
component displacement field and restoring forces determined from the ab-initio
generalized stacking fault energetics (ie., the so-called -surface).
The approach is used to investigate dislocations in L1 TiAl and CuAu;
predicted differences in the unit dislocation properties are explicitly related
with features of the -surface geometry. A unified description of
compact, spread and split dislocation cores is provided with an important
characteristic "dissociation path" revealed by this highly tractable scheme.Comment: 7 two columns pages, 2 eps figures. Phys. Rev. B. accepted November
199
Coulomb Correlations and Magnetic Anisotropy in ordered CoPt and FePt alloys
We present results of the magneto-crystalline anisotropy energy (MAE)
calculations for chemically ordered CoPt and FePt alloys taking into
account the effects of strong electronic correlations and spin-orbit coupling.
The local spin density + Hubbard U approximation (LSDA+U) is shown to provide a
consistent picture of the magnetic ground state properties when intra-atomic
Coulomb correlations are included for both 3 and 5 elements. Our results
demonstrate significant and complex contribution of correlation effects to
large MAE of these material.Comment: revised version; 4 pages, 2 figure