530 research outputs found
Effect of spin-orbit interaction on a magnetic impurity in the vicinity of a surface
We propose a new mechanism for surface-induced magnetic anisotropy to explain
the thickness-dependence of the Kondo resistivity of thin films of dilute
magnetic alloys. The surface anisotropy energy, generated by spin-orbit
coupling on the magnetic impurity itself, is an oscillating function of the
distance d from the surface and decays as 1/d^2. Numerical estimates based on
simple models suggest that this mechanism, unlike its alternatives, gives rise
to an effect of the desired order of magnitude.Comment: 4 pages, 4 figure
Optical properties of random alloys : Application to Cu_{50}Au_{50} and Ni_{50}Pt_{50}
In an earlier paper [K. K. Saha and A. Mookerjee, Phys. Rev. B 70 (2004) (in
press) or, cond-mat/0403456] we had presented a formulation for the calculation
of the configuration-averaged optical conductivity in random alloys. Our
formulation is based on the augmented-space theorem introduced by one of us [A.
Mookerjee, J. Phys. C: Solid State Phys. 6, 1340 (1973)]. In this communication
we shall combine our formulation with the tight-binding linear muffin-tin
orbitals (TB-LMTO) technique to study the optical conductivities of two alloys
Cu_{50}Au_{50} and Ni_{50}Pt_{50}.Comment: 5 pages, 7 figure
Temperature dependent magnetic anisotropy in metallic magnets from an ab-initio electronic structure theory: L1_0-ordered FePt
On the basis of a first-principles, relativistic electronic structure theory
of finite temperature metallic magnetism, we investigate the variation of
magnetic anisotropy, K, with magnetisation, M, in metallic ferromagnets. We
apply the theory to the high magnetic anisotropy material, L1_0-ordered FePt,
and find its uniaxial K consistent with a magnetic easy axis perpendicular to
the Fe/Pt layering for all M and to be proportional to M^2 for a broad range of
values of M. For small M, near the Curie temperature, the calculations pick out
the easy axis for the onset of magnetic order. Our results are in good
agreement with recent experimental measurements on this important magnetic
material.Comment: 4 pages, 2 figure
Dynamics of Ordering in Alloys with Modulated Phases
This paper presents a theoretical model for studying the dynamics of ordering
in alloys which exhibit modulated phases. The model is different from the
standard time-dependent Ginzburg-Landau description of the evolution of a
non-conserved order parameter and resembles the Swift-Hohenberg model. The
early-stage growth kinetics is analyzed and compared to the Cahn-Hilliard
theory of continuous ordering. The effects of non-linearities on the growth
kinetics are discussed qualitatively and it is shown that the presence of an
underlying elastic lattice introduces qualitatively new effects. A lattice
Hamiltonian capable of describing these effects and suitable for carrying out
simulations of the growth kinetics is also constructed.Comment: 18 pages, 3 figures (postscript files appended), Brandeis-BC9
Coarse Grained Density Functional Theories for Metallic Alloys: Generalized Coherent Potential Approximations and Charge Excess Functional Theory
The class of the Generalized Coherent Potential Approximations (GCPA) to the
Density Functional Theory (DFT) is introduced within the Multiple Scattering
Theory formalism for dealing with, ordered or disordered, metallic alloys. All
GCPA theories are based on a common ansatz for the kinetic part of the
Hohenberg-Kohn functional and each theory of the class is specified by an
external model concerning the potential reconstruction. The GCPA density
functional consists of marginally coupled local contributions, does not depend
on the details of the charge density and can be exactly rewritten as a function
of the appropriate charge multipole moments associated with each lattice site.
A general procedure based on the integration of the 'qV' laws is described that
allows for the explicit construction the same function. The coarse grained
nature of the GCPA density functional implies great computational advantages
and is connected with the O(N) scalability of GCPA algorithms. Moreover, it is
shown that a convenient truncated series expansion of the GCPA functional leads
to the Charge Excess Functional (CEF) theory [E. Bruno, L. Zingales and Y.
Wang, Phys. Rev. Lett. {\bf 91}, 166401 (2003)] which here is offered in a
generalized version that includes multipolar interactions. CEF and the GCPA
numerical results are compared with status of art LAPW full-potential density
functional calculations for 62, bcc- and fcc-based, ordered CuZn alloys, in all
the range of concentrations. These extensive tests show that the discrepancies
between GCPA and CEF are always within the numerical accuracy of the
calculations, both for the site charges and the total energies. Furthermore,
GCPA and CEF very carefully reproduce the LAPW site charges and the total
energy trends.Comment: 19 pages, 11 figure
Predictors of Therapy-Related Myelodysplasia and Acute Myeloid Leukemia (t-MDS/AML) After Autologous Hematopoietic Cell Transplantation (AHCT) for Hematologic Malignancies
The onset of magnetic order in fcc-Fe films on Cu(100)
On the basis of a first-principles electronic structure theory of finite
temperature metallic magnetism in layered materials, we investigate the onset
of magnetic order in thin (2-8 layers) fcc-Fe films on Cu(100) substrates. The
nature of this ordering is altered when the systems are capped with copper.
Indeed we find an oscillatory dependence of the Curie temperatures as a
function of Cu-cap thickness, in excellent agreement with experimental data.
The thermally induced spin-fluctuations are treated within a mean-field
disordered local moment (DLM) picture and give rise to layer-dependent `local
exchange splittings' in the electronic structure even in the paramagnetic
phase. These features determine the magnetic intra- and interlayer interactions
which are strongly influenced by the presence and extent of the Cu cap.Comment: 13 pages, 3 figure
Cluster coherent potential approximation for electronic structure of disordered alloys
We extend the single-site coherent potential approximation (CPA) to include
the effects of non-local disorder correlations (alloy short-range order) on the
electronic structure of random alloy systems. This is achieved by mapping the
original Anderson disorder problem to that of a selfconsistently embedded
cluster. This cluster problem is then solved using the equations of motion
technique. The CPA is recovered for cluster size , and the disorder
averaged density-of-states (DOS) is always positive definite. Various new
features, compared to those observed in CPA, and related to repeated scattering
on pairs of sites, reflecting the effect of SRO are clearly visible in the DOS.
It is explicitly shown that the cluster-CPA method always yields
positive-definite DOS. Anderson localization effects have been investigated
within this approach. In general, we find that Anderson localization sets in
before band splitting occurs, and that increasing partial order drives a
continuous transition from an Anderson insulator to an incoherent metal.Comment: 7 pages, 6 figures. submitted to PR
Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra
We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed
Ecto-nucleoside triphosphate diphosphohydrolase 3 in the ventral and lateral hypothalamic area of female rats: morphological characterization and functional implications
<p>Abstract</p> <p>Background</p> <p>Based on its distribution in the brain, ecto-nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) may play a role in the hypothalamic regulation of homeostatic systems, including feeding, sleep-wake behavior and reproduction. To further characterize the morphological attributes of NTPDase3-immunoreactive (IR) hypothalamic structures in the rat brain, here we investigated: 1.) The cellular and subcellular localization of NTPDase3; 2.) The effects of 17β-estradiol on the expression level of hypothalamic NTPDase3; and 3.) The effects of NTPDase inhibition in hypothalamic synaptosomal preparations.</p> <p>Methods</p> <p>Combined light- and electron microscopic analyses were carried out to characterize the cellular and subcellular localization of NTPDase3-immunoreactivity. The effects of estrogen on hypothalamic NTPDase3 expression was studied by western blot technique. Finally, the effects of NTPDase inhibition on mitochondrial respiration were investigated using a Clark-type oxygen electrode.</p> <p>Results</p> <p>Combined light- and electron microscopic analysis of immunostained hypothalamic slices revealed that NTPDase3-IR is linked to ribosomes and mitochondria, is predominantly present in excitatory axon terminals and in distinct segments of the perikaryal plasma membrane. Immunohistochemical labeling of NTPDase3 and glutamic acid decarboxylase (GAD) indicated that γ-amino-butyric-acid- (GABA) ergic hypothalamic neurons do not express NTPDase3, further suggesting that in the hypothalamus, NTPDase3 is predominantly present in excitatory neurons. We also investigated whether estrogen influences the expression level of NTPDase3 in the ventrobasal and lateral hypothalamus. A single subcutaneous injection of estrogen differentially increased NTPDase3 expression in the medial and lateral parts of the hypothalamus, indicating that this enzyme likely plays region-specific roles in estrogen-dependent hypothalamic regulatory mechanisms. Determination of mitochondrial respiration rates with and without the inhibition of NTPDases confirmed the presence of NTPDases, including NTPDase3 in neuronal mitochondria and showed that blockade of mitochondrial NTPDase functions decreases state 3 mitochondrial respiration rate and total mitochondrial respiratory capacity.</p> <p>Conclusion</p> <p>Altogether, these results suggest the possibility that NTPDases, among them NTPDase3, may play an estrogen-dependent modulatory role in the regulation of intracellular availability of ATP needed for excitatory neuronal functions including neurotransmission.</p
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