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Previous issue date: 2010 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / We investigate core-shell nanowires of diluted magnetic semiconductors (DMS) with
remote n-type modulation doping. The incorporation of Mn2 ions acting as spin 5/2 impurities
in the core region of the wire gives rise to a strong s-d exchange coupling between electrons
in the wire and those of the d levels of the Mn2 ions. Applying an external magnetic eld
along the axis of the wire, within the mean eld approximation, the s-d exchange generates
a spin-dependent core potential. A gate voltage is applied radially to wire, to obtain some
control over the density of the wire. Electronic strucutre of the wire was calculated within
the e?ective mass approximation, in both approximations Hartree and spin density functional
theory. We calculated the conductance of wire using the Landauer-B?uttiker formulation in the
linear response regime, which generally results in a total conductance with well-de ned plateaus
in GT = 2; 6; 10G0 (G0 = e2=h is the quanta of conductance), which occurred because in the
system investigated the rst level is twofold degenerated (spin degenerescence) and the others
are fourfold degenerated (spin degenerescence and orbital angular momentum). In the absence
of a magnetic eld we observe that when we take into account the e?ects of exchange and
correlation, the states with eigenvalues of Lz nonzero will be polarized while those with l = 0
isn't polarized. This unpolarized level with eigenvalue of Lz null suggests that, perhaps, the
0.7 anomaly (the emergence of two plateau at G = 0:7G0 and the other in G = G0) quantum
wires on existing geometry of split-gate is related to the geometry of the wire. The results for
total energy show that there are a competition between the ferromagnetic and paramagnetic
states. / Investigamos nano fios de semicondutores magnéticos dilu??dos (DMSs - Diluted Magnetic
Semiconductors) do tipo caroço-casca com dopagem remota tipo-n. A incorporação dos
íons de Mn+2, que atuam como impurezas de spin 5/2 no caroço do fi o, faz surgir um forte
acoplamento de trocas dentre os eletrons do fio e aqueles dos níveis d do íon Mn+2. Com a
aplicação de um campo magnético externo ao longo do eixo do fi o, na aproximação de campo
médio, a interação de troca s-d gera um potencial dependente do spin na região do caroço do
fi o. Um potencial de gate é aplicado radialmente ao nanofi o, para obtermos um certo controle
sobre a densidade eletrônica do fi o. Calculamos a estrutura eletrônica do nanofi o de
DMSs usando o modelo da massa efetiva, tanto na aproximação de Hartree quanto na teoria
do funcional da densidade dependente de spin (SDFT - Spin Density Functional Theory).
Calculamos a condutância do nano fio usando a formulação de Landauer-B?uttiker no regime de
resposta linear, o que de modo geral, resultou numa condutância total com platôs bem de finidos
em GT = 2; 6; 10G0 (G0 = e2=h ?e o quanta de condutância), o que ocorreu porque no sistema
investigado a primeira subbanda ?e duplamente degenerada (degenerescência de spin) e as outras
duas são quadruplamente degenerada (degenerescência de spin e de momento angular orbital).
Na ausência de um campo magnético observamos que ao levarmos em conta os efeitos de troca
e correlação, os estados que possuem autovalor de Lz diferente de zero se polarizam enquanto
que os que possuem l = 0 não se polarizam. Essa não-polarização do nível com autovalor de Lz
nulo sugere que, talvez, a anomalia 0,7 (o surgimento de dois platôs um em G = 0; 7G0 e outro
em G = G0) existente em os quânticos com geometria de split-gate esteja relacionada com a
geometria do o. Os resultados obtidos para a energia total mostram que há uma competição
entre os estados ferromagnético e paramagnéticos.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.bc.ufg.br:tde/2888 |
| Date | January 2010 |
| Creators | Mendes, Udson Cabra |
| Contributors | Avelar, Ardiley Torres, Leão, Salvino de Araújo |
| Publisher | Universidade Federal de Goiás, Programa de Pós-graduação em Fisica (IF), UFG, Brasil, Instituto de Física - IF (RG) |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da UFG, instname:Universidade Federal de Goiás, instacron:UFG |
| Rights | http://creativecommons.org/licenses/by-nc-nd/4.0/, info:eu-repo/semantics/openAccess |
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