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

Relação de longo prazo entre a produtividade do arroz irrigado produzido no Rio Grande do Sul e de Santa Catarina.

O objetivo geral deste trabalho foi analisar a relação entre a produtividade do arroz irrigado no Rio Grande do Sul e de Santa Catarina. A análise de co-integração de Engle e Granger (1987) foi utilizada com forma de corroborar com a ideia de relação de longo prazo entres as produtividades dos arrozais

Margens de comercialização no mercado de arroz em São Paulo, 05/2010 a 04/2013.

O presente trabalho buscou analisar a comercialização do arroz entre 05/2010 e 04/2013 sob a ótica das margens de comercialização nos níveis de produtor, atacado e varejo, em São Paulo. Pretende-se, assim, demonstrar a participação dos diferentes agentes no valor adicionado ao produto arroz

Competitividade dos principais produtos agropecuários do Brasil - vantagem comparativa revelada normalizada.

Este trabalho visa analisar a competitividade dos principais produtos agropecuários brasileiros por meio de um índice alternativo, o índice de vantagem comparativa revelada normalizado (VCRN), no período entre 1996 e 2007