Interlayer Exchange Coupling in (Ga,Mn)As-based Superlattices

The interlayer coupling between (Ga,Mn)As ferromagnetic layers in all-semiconductor superlattices is studied theoretically within a tight-binding model, which takes into account the crystal, band and magnetic structure of the constituent superlattice components. It is shown that the mechanism originally introduced to describe the spin correlations in antiferromagnetic EuTe/PbTe superlattices, explains the experimental results observed in ferromagnetic semiconductor structures, i.e., both the antiferromagnetic coupling between ferromagnetic layers in IV-VI (EuS/PbS and EuS/YbSe) superlattices as well as the ferromagnetic interlayer coupling in III-V ((Ga,Mn)As/GaAs) multilayer structures. The model allows also to predict (Ga,Mn)As-based structures, in which an antiferromagnetic interlayer coupling could be expected.Comment: 4 pages, 3 figure

Crystal and electronic structure of PbTe/CdTe nanostructures

In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron density of states (DOS) of the systems. In contrast to the ab initio methods, the latter allows studying nanostructures with diameters comparable to the real ones. The calculations show that both kinds of inclusions lead to changes of the DOS of the carriers near the Fermi level, which may affect optical, electrical and thermoelectric properties of the material. These changes depend on the size, shape, and concentration of inclusions

Spin-dependent tunneling in modulated structures of (Ga,Mn)As

A model of coherent tunneling, which combines multi-orbital tight-binding approximation with Landauer-B\"uttiker formalism, is developed and applied to all-semiconductor heterostructures containing (Ga,Mn)As ferromagnetic layers. A comparison of theoretical predictions and experimental results on spin-dependent Zener tunneling, tunneling magnetoresistance (TMR), and anisotropic magnetoresistance (TAMR) is presented. The dependence of spin current on carrier density, magnetization orientation, strain, voltage bias, and spacer thickness is examined theoretically in order to optimize device design and performance.Comment: 9 pages, 13 figures, submitted to PR

Recursos e capacidades necessários para a transição entre o modelo de negócios tradicional e o modelo de negócios digital : estudo de casos múltiplos

Para sobreviver a rápida transformação de mercado e a mudança na forma como se atende aos clientes e assim ter sucesso em seus nichos, a eficácia com que as empresas apropriam-se de novas tecnologias tornou-se um fator chave. Em um ambiente onde cada vez mais as informações estão acessíveis, possuir recursos e capacidades dinâmicas únicos às empresas faz-se imprescindível ao sucesso no meio digital. A partir desse cenário, o presente estudo propõe-se a analisar de que maneira os recursos na ótica da teoria da Visão Baseada em Recursos e Capacidades Dinâmicas influenciam na transformação do modelo de negócios tradicional para o modelo de negócios digital, e para tal faz-se o estudo de caso nas empresas A e B, ambas do setor de joias e semijoias e em processo de transição de modelo há três anos. O método utilizado na pesquisa foi o de estudo de casos múltiplos de caráter exploratório e de análise qualitativa. O instrumento de coleta de dados foi um questionário de roteiro semiestruturado de questões abertas e baseado na literatura abordada. Como resultado de pesquisa, as empresas elencaram as dimensões “conteúdo”, “valor” e “agilidade” como fatores mais importantes para a transição do modelo de negócios porém, de alguma maneira, todas as dimensões elencadas foram trazidas como importantes pelos entrevistados, o que corroborou para o entendimento de que os recursos e capacidades dinâmicas são inter-relacionados, validando o modelo de pesquisa proposto pela autora.In order to survive to the quick market transformation and the change in the way customers are catered, and by that succeed in their niches, the effectiveness with which companies appropriate the new technologies has become a key factor. In an environment where the information is increasingly accessible, having unique resources and dynamic capabilities is essential for the companies to succeed in the digital world. From this scenario, the present study proposes to analyze how resources and dynamic capabilities influence the transformation of the traditional business model into the digital business model. For this purpouse companies A and B, both in the jewelery sector and in the process of business model transition for three years, are studied. The method used in this research was the exploratory multiple cases study and qualitative analysis. The data collection instrument used was a semi-structured questionnaire with open questions based on the literature. As a result of the research, the companies listed the dimensions "content", "value" and "agility" as the most important factors for the transition of the business model, but somehow, all the dimensions listed were brought as important by the interviewees, which corroborated for the understanding that resources and dynamic capacities are interrelated, validating the research model proposed by the author

Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs

The recently reported Rutherford backscattering and particle-induced X-ray emission experiments have revealed that in low-temperature MBE grown GaMnAs a significant part of the incorporated Mn atoms occupies tetrahedral interstitial sites in the lattice. Here we study the magnetic properties of these interstitial ions. We show that they do not participate in the hole-induced ferromagnetism. Moreover, Mn interstitial double donors may form pairs with the nearest substitutional Mn acceptors - our calculations evidence that the spins in such pairs are antiferromagnetically coupled by the superexchange. We also show that for the Mn ion in the other, hexagonal, interstitial position (which seems to be the case in the GaMnBeAs samples) the p-d interactions with the holes, responsible for the ferromagnetism, are very much suppressed.Comment: 4 pages, 3 figures, submitted to PR