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Complex spin configurations in thin films heterostructures
Full text linkEsta Tese consiste de um estudo experimental sobre a formação de texturas magnéticas em heteroestruturas do tipo filmes finos bi, tri e multicamadas. A investigação é feita através de medidas de magnetização, propriedades de magnetotransporte elétrico e imageamento por magneto-óptica. Foram produzidos e estudados dois tipos principais de heteroestruturas: (i) filmes bicamadas e multicamadas de Co/Ru e Co/Pd e (ii) filmes de Nb/Al2O3/Co. Os resultados de resistividade elétrica, magnetorresistência e efeito Hall para as bicamadas de Co/Ru e Co/Pd foram analisados com base num modelo de condução por duas correntes em paralelo, com mistura de correntes. A partir desta análise, juntamente com os resultados de magnetização, identificam-se efeitos de interface entre as camadas componentes da heteroestrutura. Os resultados sugerem a formação de texturas magnéticas não triviais na região da interface. Em razão da forte interação spin-órbita no Ru e, principalmente, no Pd supõe-se que efeitos da interação Dzyaloshinskii-Moriya sejam relevantes para a estabilização das texturas de spin na interface Também são apresentados e discutidos resultados de medidas de transporte elétrico e imageamento por magneto-óptica em filmes finos de estrutura Nb/Al2O3/Co. Nestas amostras foi observada uma correlação entre as propriedades de magnetotransporte medidas na camada de Co e o regime de penetração de fluxo magnético na camada supercondutora. Desta forma, essa estrutura híbrida mostrou-se útil para detecção de penetração de fluxo na forma de avalanches na camada supercondutora. Além disso, em todas as amostras investigadas observou-se a indução de uma textura de spin na camada ferromagnética que reproduz a geometria dendrítica das avalanches de fluxo na camada supercondutora. Tais texturas, impressas no filme ferromagnético, são estáveis em temperaturas muito superiores à temperatura crítica do Nb. Os resultados de imageamento magneto-óptico mostram que os dendritos magnéticos possuem uma estrutura interna não trivial, que depende da magnetização prévia da camada de Co.This Thesis consists of an experimental study on the formation of magnetic textures in heterostructures composed by thin films bi, tri and multilayers. Magnetization, magnetotransport properties and magneto-optical imaging measurements were carried out as function of temperature and magnetic field. Two types of heterostructures were investigated: (i) Co/Ru and Co/Pd bilayers and multilayers and (ii) Nb/Al2O3/Co. The resistivity, magnetoresistance and Hall effect results for Co/Ru and Co/Pd were analysed using a two current conduction model, with current mixing. From this analysis, complemented by magnetization results, effects from the interface between adjacent layers are identified. These results suggests the formation of non-trivial textures in the interface. Owing to the spin-orbit interaction from Ru and mainly from Pd, it is suggested that the Dzyaloshinskii-Moriya plays an important role for the stabilization of those interfacial spin textures. Magnetotransport results and magneto-optical imaging measurements in Nb/Al2O3/Co heterostructures are presented and discussed. It was observed that the magnetotransport measurements in the Co layer is strongly correlated to the magnetic flux penetration regime in the superconducting layer. Consequently, our heterostructure appears to be a useful tool to detect flux avalanches in the superconducting layer. Besides, in all investigated samples magnetic textures were induced in the ferromagnetic layer. The textures mimic the dendritic form of the avalanches. Such magnetic textures are stable up temperatures far larger than the superconducting transition for Nb. The magneto-optical imaging results show that these imprinted dendritic textures have a non-trivial internal structure which depends on the initial magnetic state in Co
Efeitos de desordem química da densidade de corrente e na força de "pinning" de monocristais de YBa2Cu3O7-δ1
No full textThis work relates to the realization of an experimental study about the effects coming from the Ba partial substitution for Sr in the YBa2Cu3O7-δ superconductor upon the critical current, JC(H,T), and flux pinning mechanisms. For this purpose were grown single crystals samples of YBa2-xSrxCu3O7- with (x = 0; 0.02; 0.1; 0.25; 0.37). The crystals structure was analyzed by x-ray diffraction, (XRD), polarized light microscopy (PLM) and transmission electron microscopy (TEM) techniques. The XRD showed, for the indicated concentrations, that there are not different phases in addition to the orthorhombic structure of the YBa2Cu3O7-. The PLM and TEM images for the single crystal YBa1,75Sr0,25Cu3O7- showed the existence of a structure made by the arrangement of twins and small inclusions, possible associated by the presence of Sr atoms clusters. The DC magnetic measures as a function of the magnetic field, M(H and temperature, M(T), were performed done in an SQUID MPMS-XL magnetometer with the purpose to get the magnetic irreversibility field, Hirr(T) and critical current density, JC(H,T) that was calculated by the extended Bean model application. The behavior of the higher density pinning force, FP,Max(H,T), was obtained by the expression = . The pinning mechanisms were analyzed by the determination of the behavior of the reduced pinning force, f(h), where f(h) = FP/FP,Max and h=H/Hirr. The arrangement of the f(h) data was compared with the Dew-Hughes model scale functions. In a usual way, the results of JC(H,T) and f(h) showed that the dominant pinning mechanisms in the YBa2Cu3O7-, when the Ba was replaced by at least 18.5% for Sr, are the normal point and normal surface pinning mechanisms. Where the normal point pinning relevance was observed to x < 12.5% that coincided with the observation of the highest JC(T) values transported by 1% and 5% Sr doped samples when compared with the pure sample.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESEste trabalho refere-se à realização de um estudo experimental sobre os efeitos provenientes da substituição parcial de Ba por átomos de Sr no supercondutor YBa2Cu3O7-δ na densidade de corrente crítica, JC(H,T), e nos mecanismos de “flux pinning” desse material. Para tanto foram crescidos monocristais de YBa2-xSrxCu3O7- com (x = 0; 0,02; 0,1; 0,25; 0,37). Esses tiveram a sua estrutura analisada por meio das técnicas de difração de raio-x, (XRD) microscopia de luz polarizada (PLM) e microscopia eletrônica de transmissão (TEM). Os difratogramas de XRD revelaram que, para as concentrações indicadas, não há presença de fases espúrias a estrutura ortorrômbica do YBa2Cu3O7-. As imagens obtidas a partir das técnicas de PLM e TEM para o monocristal YBa1,75Sr0,25Cu3O7- revelaram a existência de uma estrutura composta pelo arranjo de maclas e pequenas inclusões, possivelmente associadas a segregação de átomos de Sr. Foram realizadas medidas de magnetização DC em função do campo, M(H e da temperatura, M(T), utilizando um magnetômetro SQUID MPMS-XL. Com o propósito de obter o campo de irreversibilidade magnética, Hirr(T) e da densidade de corrente crítica, JC(H,T). Sendo esta última determinada do modelo de Bean estendido. O comportamento da densidade de força de “pinning”, FP(H,T) foi obtido da expressão = . Os mecanismos de “pinning” foram analisados a partir da determinação do comportamento da força de “pinning” reduzida, f(h), sendo f(h) = FP/F P,Max e h=H/Hirr. A disposição dos dados de f(h) foi comparada com as funções de escala do modelo de Dew-Hughes para os mecanismos de “pinning”. De maneira geral os resultados de JC(H,T) e f(h) revelaram que os mecanismos de “pinning” dominantes no YBa2Cu3O7- quando o Ba foi substituído por até 18,5% de Sr são o normal pontual e o normal superficial sendo que a preponderância do “pinning” normal pontual foi observado para x < 12,5% o que coincidiu com a observação da melhor performance de JC(T) para as amostras dopadas com 1% e 5% de Sr em relação a amostra pura
Efeitos de desordem química da densidade de corrente e na força de "pinning" de monocristais de YBa2Cu3O7-δ1
No full textThis work relates to the realization of an experimental study about the effects coming from the Ba partial substitution for Sr in the YBa2Cu3O7-δ superconductor upon the critical current, JC(H,T), and flux pinning mechanisms. For this purpose were grown single crystals samples of YBa2-xSrxCu3O7- with (x = 0; 0.02; 0.1; 0.25; 0.37). The crystals structure was analyzed by x-ray diffraction, (XRD), polarized light microscopy (PLM) and transmission electron microscopy (TEM) techniques. The XRD showed, for the indicated concentrations, that there are not different phases in addition to the orthorhombic structure of the YBa2Cu3O7-. The PLM and TEM images for the single crystal YBa1,75Sr0,25Cu3O7- showed the existence of a structure made by the arrangement of twins and small inclusions, possible associated by the presence of Sr atoms clusters. The DC magnetic measures as a function of the magnetic field, M(H and temperature, M(T), were performed done in an SQUID MPMS-XL magnetometer with the purpose to get the magnetic irreversibility field, Hirr(T) and critical current density, JC(H,T) that was calculated by the extended Bean model application. The behavior of the higher density pinning force, FP,Max(H,T), was obtained by the expression = . The pinning mechanisms were analyzed by the determination of the behavior of the reduced pinning force, f(h), where f(h) = FP/FP,Max and h=H/Hirr. The arrangement of the f(h) data was compared with the Dew-Hughes model scale functions. In a usual way, the results of JC(H,T) and f(h) showed that the dominant pinning mechanisms in the YBa2Cu3O7-, when the Ba was replaced by at least 18.5% for Sr, are the normal point and normal surface pinning mechanisms. Where the normal point pinning relevance was observed to x < 12.5% that coincided with the observation of the highest JC(T) values transported by 1% and 5% Sr doped samples when compared with the pure sample.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESEste trabalho refere-se à realização de um estudo experimental sobre os efeitos provenientes da substituição parcial de Ba por átomos de Sr no supercondutor YBa2Cu3O7-δ na densidade de corrente crítica, JC(H,T), e nos mecanismos de “flux pinning” desse material. Para tanto foram crescidos monocristais de YBa2-xSrxCu3O7- com (x = 0; 0,02; 0,1; 0,25; 0,37). Esses tiveram a sua estrutura analisada por meio das técnicas de difração de raio-x, (XRD) microscopia de luz polarizada (PLM) e microscopia eletrônica de transmissão (TEM). Os difratogramas de XRD revelaram que, para as concentrações indicadas, não há presença de fases espúrias a estrutura ortorrômbica do YBa2Cu3O7-. As imagens obtidas a partir das técnicas de PLM e TEM para o monocristal YBa1,75Sr0,25Cu3O7- revelaram a existência de uma estrutura composta pelo arranjo de maclas e pequenas inclusões, possivelmente associadas a segregação de átomos de Sr. Foram realizadas medidas de magnetização DC em função do campo, M(H e da temperatura, M(T), utilizando um magnetômetro SQUID MPMS-XL. Com o propósito de obter o campo de irreversibilidade magnética, Hirr(T) e da densidade de corrente crítica, JC(H,T). Sendo esta última determinada do modelo de Bean estendido. O comportamento da densidade de força de “pinning”, FP(H,T) foi obtido da expressão = . Os mecanismos de “pinning” foram analisados a partir da determinação do comportamento da força de “pinning” reduzida, f(h), sendo f(h) = FP/F P,Max e h=H/Hirr. A disposição dos dados de f(h) foi comparada com as funções de escala do modelo de Dew-Hughes para os mecanismos de “pinning”. De maneira geral os resultados de JC(H,T) e f(h) revelaram que os mecanismos de “pinning” dominantes no YBa2Cu3O7- quando o Ba foi substituído por até 18,5% de Sr são o normal pontual e o normal superficial sendo que a preponderância do “pinning” normal pontual foi observado para x < 12,5% o que coincidiu com a observação da melhor performance de JC(T) para as amostras dopadas com 1% e 5% de Sr em relação a amostra pura
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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