Silvia Hunold Lara

Indirect interactions between localized magnetic moments in intrinsic semiconductors

Abstract The indirect interaction between localized magnetic moments in insulators and semiconductors is investigated at T = 0°K. This interaction arises from virtual excitations of the valence electrons to the conduction band and is oscillatory as a function of distance. The passage from the case of small gap semiconductors to insulators is studied in detail, as a function of the energy gap and the effective masses. The Bloembergen-Rowland interaction is derived as a limiting case for insulators. Possible applications are also discussed.

Indirect interactions between localized magnetic moments in doped semiconductors

The coupling between localized magnetic moments via conduction electrons is calculated taking into account the temperature and the mean free path of the electrons. For a fully degenerate electron gas and an infinite electronic mean free path the oscillatory RKKY interaction is obtained. On the limit of Boltzmann population and for infinite electronic mean free path the interaction can only be ferromagnetic. Taking into account the electronic mean free path the possibility of antiferromagnetism is restored. Furthermore the range of the interaction decreases. Several intermediate cases and possible applications are discussed.

On the origin of the exchange interaction in EuO and EuS

Abstract The indirect magnetic interaction in semiconductors is used to evaluate the exchange parameters for EuO and EuS respectively which yields J eff (EuO)≅(0.06 ± 0.02) eV and J eff (EuS)≅(0.08 ± 0.04) eV.

Effects of finite temperatures, valence bands and energy gaps on the indirect exchange interaction in intrinsic semiconductors

Abstract The indirect exchange interaction between localized magnetic moments via virtual excitations from the valence band in intrinsic semiconductors is calculated taking into account the temperature, energy gaps, finite valence bands and effective masses. The inclusion of finite temperature effects changes significantly the phase and magnitude of the oscillations. For small gap semiconductors the oscillatory character and the possibility of ferro-magnetic as well as anti-ferromagnetic coupling are obtained. The exchange interaction oscillates with temperature suggesting interesting applications of this model.

Effects of the mean free path and energy gaps on the indirect interaction in semiconductors and insulators

The indirect exchange interaction between localised magnetic moments by way of virtual excitations from the valence band is calculated in semiconductors and insulators taking into account the mean free path energy gaps, finite valence bands and effective masses. The decreasing mean free path weakens the interaction and also changes the phase of the oscillations. As the energy gap increases the oscillations become increasingly damped. The exchange interactions oscillate with the mean free path suggesting interesting applications of this model. For small gap semiconductors the effects of the mean free path are more important than the energy gap whereas the relative effect of these two parameters are competitive in an insulator.

Finite temperature effects on the indirect exchange interaction in intrinsic semiconductors

Abstract The indirect exchange interaction between localized magnetic moments via virtual excitations from the valence band in intrinsic semiconductors is calculated taking into account finite temperatures and band structure parameters which modify the exchange interaction and results in an oscillatory behaviour with temperature.

As “hordas selvagens” no Império do Brasil: a legislação indigenista brasileira oitocentista.

As “hordas selvagens”no Império do Brasil: a legislação indigenista brasileira. Laila T. Correa e Silva (IC) Resumo Este projeto contribui para o trabalho coletivo de elaboração de um instrumento de pesquisa que sistematiza a legislação sobre o trabalho e os trabalhadores no Brasil, em Portugal e na África de colonização portuguesa. Trabalhamos inserindo informações sobre a legislação indigenista brasileira produzida no século XIX, entre 1808 e 1889, na base de dados “Legislação: Trabalhadores e Trabalho em Portugal, Brasil e África Colonial Portuguesa”, disponível em http: //www.ifch.unicamp.br/cecult/lex/web/. Além dessa atividade, desenvolvemos uma reflexão acerca da legislação indigenista do século XIX, em especial, sobre o trabalho indígena e sua íntima relação com a questão de terras no período Imperial. Palavras Chave: Brasil Império, Legislação indigenista, Lei de terras.