281 research outputs found
Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures
The occurrence of inhomogeneous spin-density distribution in multilayered
ferromagnetic diluted magnetic semiconductor nanostructures leads to strong
dependence of the spin-polarized transport properties on these systems. The
spin-dependent mobility, conductivity and resistivity in
(Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a
function of temperature, scaled by the average magnetization of the diluted
magnetic semiconductor layers. An increase of the resistivity near the
transition temperature is obtained. We observed that the spin-polarized
transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure
Charge and spin distributions in GaMnAs/GaAs Ferromagnetic Multilayers
A self-consistent electronic structure calculation based on the
Luttinger-Kohn model is performed on GaMnAs/GaAs multilayers. The Diluted
Magnetic Semiconductor layers are assumed to be metallic and ferromagnetic. The
high Mn concentration (considered as 5% in our calculation) makes it possible
to assume the density of magnetic moments as a continuous distribution, when
treating the magnetic interaction between holes and the localized moment on the
Mn(++) sites. Our calculation shows the distribution of heavy holes and light
holes in the structure. A strong spin-polarization is observed, and the charge
is concentrated mostly on the GaMnAs layers, due to heavy and light holes with
their total angular momentum aligned anti-parallel to the average
magnetization. The charge and spin distributions are analyzed in terms of their
dependence on the number of multilayers, the widths of the GaMnAs and GaAs
layers, and the width of lateral GaAs layers at the borders of the structure.Comment: 12 pages,7 figure
Hysteresis in the Random Field Ising Model and Bootstrap Percolation
We study hysteresis in the random-field Ising model with an asymmetric
distribution of quenched fields, in the limit of low disorder in two and three
dimensions. We relate the spin flip process to bootstrap percolation, and show
that the characteristic length for self-averaging increases as in 2d, and as in 3d, for disorder
strength much less than the exchange coupling J. For system size , the coercive field varies as for
the square lattice, and as on the cubic lattice.
Its limiting value is 0 for L tending to infinity, both for square and cubic
lattices. For lattices with coordination number 3, the limiting magnetization
shows no jump, and tends to J.Comment: 4 pages, 4 figure
Demagnetization via Nucleation of the Nonequilibrium Metastable Phase in a Model of Disorder
We study both analytically and numerically metastability and nucleation in a
two-dimensional nonequilibrium Ising ferromagnet. Canonical equilibrium is
dynamically impeded by a weak random perturbation which models homogeneous
disorder of undetermined source. We present a simple theoretical description,
in perfect agreement with Monte Carlo simulations, assuming that the decay of
the nonequilibrium metastable state is due, as in equilibrium, to the
competition between the surface and the bulk. This suggests one to accept a
nonequilibrium "free-energy" at a mesoscopic/cluster level, and it ensues a
nonequilibrium "surface tension" with some peculiar low-T behavior. We
illustrate the occurrence of intriguing nonequilibrium phenomena, including:
(i) Noise-enhanced stabilization of nonequilibrium metastable states; (ii)
reentrance of the limit of metastability under strong nonequilibrium
conditions; and (iii) resonant propagation of domain walls. The cooperative
behavior of our system may also be understood in terms of a Langevin equation
with additive and multiplicative noises. We also studied metastability in the
case of open boundaries as it may correspond to a magnetic nanoparticle. We
then observe burst-like relaxation at low T, triggered by the additional
surface randomness, with scale-free avalanches which closely resemble the type
of relaxation reported for many complex systems. We show that this results from
the superposition of many demagnetization events, each with a well- defined
scale which is determined by the curvature of the domain wall at which it
originates. This is an example of (apparent) scale invariance in a
nonequilibrium setting which is not to be associated with any familiar kind of
criticality.Comment: 26 pages, 22 figure
Application of the ANP to the prioritization of project stakeholders in the context of responsible research and innovation
[EN] This paper presents a methodology to assess the stakeholders¿ influence in a research project within the context of responsible research and innovation. The methodology is based on a combination of the multicriteria decision making technique analytic network process and the key areas of responsible research. The method allows ranking and ordering the project¿s stakeholders based on their influence upon its responsibility. The purpose of such an assessment is to help research teams to more efficiently devote their limited resources to stakeholder management. The procedure is applied to a case study of the Information and Communication Technology business sector. It is an ongoing project at an early phase of development. Influential stakeholders have been identified first, and have been further classified into groups based on their relative importance. The assessment of their influence has been based on up to 16 different criteria, mainly belonging to the framework of responsible research and innovation. In the case study, the most influential criterion was the Capability to promote public engagement, while Developers were found to be the stakeholders most contributing to the research project responsibility. However, as explained, this is a temporary situation, valid for the current project development situation. It may vary over time as criteria vary in weight and stakeholders vary in influence.The authors would like to thank to our anonymous referees for their constructive comments and suggestions that helped us to improve the quality of the paper. Also, to the “Bolívar Gana con Ciencia” program from the Gobernación de Bolívar (Colombia) for the financial support. For the same reason, the authors are grateful to the Spanish Agencia Estatal de Investigación for its support of the project Propuesta de Indicadores para Impulsar el Diseño de Una Política Orientada al Desarrollo de Investigación e Innovación Responsable en España (CSO2016-76828-R)Ligardo-Herrera, I.; Gómez-Navarro, T.; Gonzalez-Urango, H. (2018). Application of the ANP to the prioritization of project stakeholders in the context of responsible research and innovation. Central European Journal of Operations Research. 1-23. https://doi.org/10.1007/s10100-018-0573-4S123Akbari N, Irawan CA, Jones DF, Menachof D (2017) A multi-criteria port suitability assessment for developments in the offshore wind industry. Renew Energy 102:118–133. https://doi.org/10.1016/j.renene.2016.10.035Aragonés-Beltrán P, García-Melón M, Montesinos-Valera J (2017) How to assess stakeholders’ influence in project management? A proposal based on the analytic network process. 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