On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer

A self-consistent calculation of the density of states and the spectral density function is performed in a two-dimensional spin-polarized hole system based on a multiple-scattering approximation. Using parameters corresponding to GaMnAs thin layers, a wide range of Mn concentrations and hole densities have been explored to understand the nature, localized or extended, of the spin-polarized holes at the Fermi level for several values of the average magnetization of the Mn ystem. We show that, for a certain interval of Mn and hole densities, an increase on the magnetic order of the Mn ions come together with a change of the nature of the states at the Fermi level. This fact provides a delocalization of spin-polarized extended states anti-aligned to the average Mn magnetization, and a higher spin-polarization of the hole gas. These results are consistent with the occurrence of ferromagnetism with relatively high transition temperatures observed in some thin film samples and multilayered structures of this material.Comment: 3 page

Magnetic ordering in GaAlAs:Mn double well structure

The magnetic order in the diluted magnetic semiconductor barrier of double AlAs/GaAs: Mn quantum well structures is investigated by Monte Carlo simulations. A confinement adapted RKKY mechanism is implemented for indirect exchange between Mn ions mediated by holes. It is shown that, depending on the barrier width and the hole concentration a ferromagnetic or a spin-glass order can be established.Comment: 3 figure

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

A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers

We investigate the spin-polarized transport of GaMnAs nanolayers in which a ferromagnetic order exists below a certain transition temperature. Our calculation for the self-averaged resistivity takes into account the existence of an impurity band determining the extended ("metallic" transport) or localized (hopping by thermal excitation) nature of the states at and near the Fermi level. Magnetic order and resistivity are inter-related due to the influence of the spin polarization of the impurity band and the effect of the Zeeman splitting on the mobility edge. We obtain, for a given range of Mn concentration and carrier density, a "metallic" behavior in which the transport by extended carriers dominates at low temperature, and is dominated by the thermally excited localized carriers near and above the transition temperature. This gives rise to a conspicuous hump of the resistivity which has been experimentally observed and brings light onto the relationship between transport and magnetic properties of this material

Estudos de Solos do Município de Aceguá, RS

bitstream/item/130155/1/Circular-157.pd

Tracking the relationship between euro area equities and sovereign bonds

This paper explores the relationship between stocks and sovereign bonds by means of the asymmetric detrended cross-correlation analysis (ADCCA). Drawing on data from 1999.01 to 2018.09 of the first wave of euro area countries, the full sample is divided into three subsets in accordance with economic and financial features. Some findings arise with striking implications for investors and policymakers. Firstly, empirical results show that cross-correlations differ from country to country, depending on the sub-period under analysis and on the time scale. Secondly, likewise within country estimates, cross-country linkages may point to fragmentation in the euro area with agents moving away from financial assets of lower-rated countries to invest in more robust economies in periods of turmoil. Thirdly, there is evidence of asymmetry since 'flight-to-quality' movements seem to be more relevant than 'flight-to-yield' episodes. Finally, while relationships were globally bidirectional until mid-2007, new causality patterns arose with the financial crisis.info:eu-repo/semantics/publishedVersio

Section efficace de la réaction 16O(t, n) 18F application au dosage de l'oxygène

Des échantillons de tantale oxydés anodiquement ont été irradiés avec des tritons de 1,6 à 3,7 MeV. La section efficace a été déterminée par mesure de la radioactivité du 18F. La valeur trouvée à 2 MeV est de 220 mb. Nos résultats sont en désaccord avec les valeurs publiées par Jarmie jusqu'à 2,2 MeV et avec la forme de la courbe obtenue par Barrandon et Albert entre 2 et 3 MeV. La réaction 16O(t, n) 18F a été utilisée pour doser l'oxygène à la surface d'échantillons d'acier inoxydable. Une limite de détection de 0,004 μg.cm-2 a été obtenue à 2 MeV, après 10 min. d'irradiation avec un faisceau de 0,2 μA de tritons. Les possibilités d'application aux dosages dans la masse sont discutées

Estimação da equação de demanda brasileira por importação de arroz do Uruguai.

Considerando que o Uruguai é outro importante exportador de arroz para o Brasil, esse estudo vem preencher a lacuna sobre o tema, tendo como objetivo principal estimar a equação de demanda por importação de arroz deste país