973 research outputs found
Coordination Dependence of Hyperfine Fields of 5sp Impurities on Ni Surfaces
We present first-principles calculations of the magnetic hyperfine fields H
of 5sp impurities on the (001), (111), and (110) surfaces of Ni. We examine the
dependence of H on the coordination number by placing the impurity in the
surfaces, on top of them at the adatom positions, and in the bulk. We find a
strong coordination dependence of H, different and characteristic for each
impurity. The behavior is explained in terms of the on-site s-p hybridization
as the symmetry is reduced at the surface. Our results are in agreement with
recent experimental findings.Comment: 4 pages, 3 figure
Optical Conductivity of Ferromagnetic Semiconductors
The dynamical mean field method is used to calculate the frequency and
temperature dependent conductivity of dilute magnetic semiconductors.
Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism
Consistency of local perceptions of climate change in the Kangchenjunga Himalaya landscape
The Himalaya is experiencing rapid climate change that is likely to significantly impact local ecosystems,
biodiversity, agriculture and human well-being. However, the scientific community has been slow to examine the extent and consequences of climate change. Local communities have been coping with environmental change since millennia. Thus they often have considerable knowledge about environmental change and means to cope with its consequences. We (a) examined the perceptions
of local communities about climate change and its impacts on ecosystems, biodiversity, agriculture and livelihoods in the Kangchenjunga Himalayas region; (b) analysed the consistency of perceptions across geographical regions, and (c) assessed the conformity between local perceptions
and scientific evidence. Our study is based on surveys conducted in 576 households, focus group discussions, key informant surveys and direct observations. The results show that people in the Kangchenjunga Himalayas region have considerable knowledge of climate change and its
effects on the weather, ecosystems, biodiversity and agriculture. These perceptions are consistent across the region and conform to scientific findings
Transition temperature of ferromagnetic semiconductors: a dynamical mean field study
We formulate a theory of doped magnetic semiconductors such as
GaMnAs which have attracted recent attention for their possible use
in spintronic applications. We solve the theory in the dynamical mean field
approximation to find the magnetic transition temperature as a function
of magnetic coupling strength and carrier density . We find that
is determined by a subtle interplay between carrier density and magnetic
coupling.Comment: 4 pages, 4 figure
Photoemission studies of GaMnAs: Mn-concentration dependent properties
Using angle-resolved photoemission, we have investigated the development of
the electronic structure and the Fermi level pinnning in GaMnAs
with Mn concentrations in the range 1--6%. We find that the Mn-induced changes
in the valence-band spectra depend strongly on the Mn concentration, suggesting
that the interaction between the Mn ions is more complex than assumed in
earlier studies. The relative position of the Fermi level is also found to be
concentration-dependent. In particular we find that for concentrations around
3.5--5% it is located very close to the valence-band maximum, which is in the
range where metallic conductivity has been reported in earlier studies. For
concentration outside this range, larger as well as smaller, the Fermi level is
found to be pinned at about 0.15 eV higher energy.Comment: REVTeX style; 7 pages, 3 figure
Carrier induced ferromagnetism in diluted magnetic semi-conductors
We present a theory for carrier induced ferromagnetism in diluted magnetic
semi-conductor (DMS). Our approach treats on equal footing quantum fluctuations
within the RPA approximation and disorder within CPA. This method allows for
the calculation of , magnetization and magnon spectrum as a function of
hole, impurity concentration and temperature. It is shown that, sufficiently
close to , and within our decoupling scheme (Tyablicov type) the CPA for
the itinerant electron gas reduces to the Virtual Crystal Approximation. This
allows, in the low impurity concentration and low density of carriers to
provide analytical expression for . For illustration, we consider the case
of and compare our results with available experimental data.Comment: 5 figures included. to appear in Phys. Rev. B (brief report
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