Bochum, Universiẗat, Diss., 2004. / Erscheinungsjahr an der Haupttitelstelle: 2003.

Hannover, Universiẗat, Diss., 2004.

Hannover, University, Diss., 2001.

Stuttgart, University, Diss., 2004.

Orientador: Sergio Moehlecke / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica "Gleb Wataghin" / Made available in DSpace on 2018-07-21T20:26:37Z (GMT). No. of bitstreams: 1 ParedesCampoy_JuanCarlos_M.pdf: 2857159 bytes, checksum: e2c536d3778157fc9a705378eb40fc71 (MD5) Previous issue date: 1995 / Resumo: Neste trabalho de tese, estudamos as propriedades de transporte: resistividade, magneto-resistividade e efeito Hall no composto supercondutor A-15 : Nb75Pt25. Para este fim, desenvolvemos os métodos de Van der Pauw convencional e Van der Pauw com ciclagem dos contatos. Este último está baseado no método de Van der Pauw convencional e no principio de simetria dos coeficientes cinéticos de Onsager, com o que evita-se a inversão do campo magnético na medida do efeito Hall. Confirmamos experimentalmente que ambos os métodos para medir o efeito Hall são equivalentes. Das medidas de resistividade, rxx(T); e magneto-resistividade, rxx(H), conseguimos determinar a ocorrência de um acoplamento intergranular. Destas medidas de transporte e das medidas de magnetização, elaboramos o plano HvsT deste composto. A linha de irreversibilidade ( IL ), foi obtida das medidas de magnetização e, a linha de HC2 foi obtida das medidas de transporte. Este composto mostrou ter uma ampla região reversível comparada com a observada em alguns HTS. Neste plano mostramos também alinha associada ao acoplamento Josephson, Hcj. Das medidas do efeito Hall no estado normal, rxy(H, T), usando ambos os métodos, determinamos o tipo de portadores de carga, a densidade de carga, a mobilidade dos portadores e a constante de Hall do composto Nb-Pt. As medidas do efeito Hall no estado supercondutor mostraram que o sinal medido por ambos os métodos é um sinal "não Hall". Interpretamos este resultado como devido a um tipo de movimento guiado dos vórtices ou "guided motion" / Abstract: In order to fulfil the requirements of the Master programe in Physics we have studied the transport properties: resistivity, magneto-resistivity and Hall effect in the superconducting compound A-15: Nb75Pt25. For this, we have developed a conventional Van der Pauw method and a Van der Pauw with cycling the contacts. This latter is based in the Van der Pauw method and the symmetry principIe of the kinetic coefficients of Onsager. With this, it is no more necessary to invert the magnetic field when we measure the Hall effect. We confirm experimentally that both methods are equivalents. From resistivity, rxx(T), and magneto-resistivity, rxx(H), measurements, we were able to determine the occurrence of intergranular coupling. From transport and magnetization measurements, we have build the HvsT plane for this compound. The irreversiblity line ( IL ), was generated from magnetization measurements and the HC2 line from transport measurements. This compound has shown a wide reversible region, similar to some HTS. In this plane we also show the line associated with the Josephson coupling, Hcj. From Hall effect measurements in the normal state, rxy(H,T), using both methods, we have determined the kind of charge carriers, the charge density , the carriers mobility and the Hall constant in the Nb-Pt compound. The Hall measurements in the superconducting state showed that the signal observed using both methods was a "no Hall" signal. We have interpretated this result as a kind of guided motion of the vortices in the mixed state / Mestrado / Física / Mestre em Física

A series of as-grown ZnO layers have been electrically characterised by the temperature dependent (20 – 300 K) Hall-effect technique. The ZnO layers were grown by metal organic chemical vapour deposition (MOCVD) on glass substrates under various growth conditions. The temperature dependent Hall-effect technique produced mobility and carrier concentration measurements. These measurements were found to be reproducible and reliable. The carrier concentration data for the layers was fitted by the charge balance equation to accurately determine the donor level and corresponding donor concentration as well as the acceptor concentration for each sample. The measured donor levels were found to vary from sample to sample and there is evidence from the results that the variations are related to the differing growth conditions of the layers. The mobility data was also fitted to establish the dominant electron scattering mechanisms in the layers. The dominant scattering mechanisms were found to vary from sample to sample. For most of the layers studied, the dominant scattering mechanism was found to be both the ionised impurity scattering at low temperatures (20 – 100 K) and grain boundary scattering at higher temperatures (100 – 300 K). The effects of exposing the ZnO layers to hydrogen plasma were also investigated by the temperature dependent Hall-effect technique. Findings indicate that hydrogen is readily incorporated in ZnO, leading always to an increased carrier concentration. It was further noted that incorporating hydrogen into ZnO in some layers increased the mobility while in other layers it caused a decrease in the mobility. The hydrogenated samples were subsequently annealed at 600 °C for 1 hour in argon ambient resulting in the carrier concentration reducing to its original value. This effect is attributed to hydrogen diffusing out of ZnO.

This thesis reports on two graphene-based structures that have been proposed and fabricated as possible prototypes for high-spatial-resolution Hall sensors with potential application in research on high-density magnetic recording technology such as bit patterned magnetic recording (BPMR) and other areas where the measurement of highly inhomogeneous fields is required. There is a direct graphene-metal contact in the first structure, which is named as TYPE I in this thesis, so that the anomalous Hall effect (AHE) in the ferromagnetic islands deposited on the graphene could be detected. Meanwhile, the graphene and the metal are isolated by an h-BN layer in the second structure which is named as TYPE II, so that only the stray field from the islands can be detected using the ordinary Hall effect (OHE).The transport measurements performed on TYPE I devices revealed there is no AHE or stray field signal detectable, and their Hall resistance relations are non-linear and do not pass through the origin point. A finite element simulation comparing the resistance of the empty graphene cross and the island-occupied cross indicates that the current in the graphene may not redistribute through the metallic islands due to interface current blocking, resulting in the non-appearance of the expected AHE signal. Moreover, an analysis on the data of the longitudinal magnetoresistance (MR) reveals that a two-fluid model and effective medium theory (EMT) model might be the major graphene MR mechanisms in the regime away from and near to the charge neutrality point (CNP) respectively. As a combined result of the above findings, a joint MR-Hall effect model under the condition of the presence of a pre-existing transverse offset current, is proposed to explain the unusual behaviour of the Hall measurement data of the TYPE I devices. The model gives qualitatively correct fitting for all longitudinal and transverse transport data of TYPE I devices. In addition, the nature of the graphene/metal contact is considered as the reason responsible for the non-appearance of the expected AHE and stray field signal, although further experimental work is needed, and suggested in the thesis, to clarify this issue. On the other hand, the TYPE II devices have shown their potential to be developed as a Hall sensor being able to detect a sub-micron magnetic island in the future, but there is still a large space for the performance of the devices to be improved. At the end of the thesis, future experimental work, which could lead to the eventual development of a high-sensitivity high-spatial-resolution Hall sensor on the basis of TYPE I and TYPE II structures, are suggested and described.

Orientador: Daltro Garcia Pinatti / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-07-19T02:52:59Z (GMT). No. of bitstreams: 1 Sartori_AntonioFernando_M.pdf: 1373469 bytes, checksum: c3562aab3bfee81daec7a7e2cba764e8 (MD5) Previous issue date: 1977 / Resumo: Medidas das voltagens transversal (Hall) e longitudinal (resistividade) são feitas em amostras policristalinas de Nb, com RRR = 27,7 e 5, como função do campo magnético e densidade de corrente. As medidas foram efetuadas por um método DC convencional, onde o aparelho central e um Nanavoltimetro. A amostra mais pura exibe uma mudança de sinal do ângulo de Hall o estado misto, a qual sugere-se ser devida a uma mudança da mobilidade dos portadores de corrente dentro do núcleo dos vórticeso Efeitos de aprisionamento de vórtices estão presentes e são discutidos em termos da interação elementar vórtice defeito com ajuda do modelo de Niessen e Weij Senfeld / Abstract: Not informed. / Mestrado / Física / Mestre em Física

No description available.

Ostrava as a minig town, Ostrava as a black city. The Moravian Philharmonic Orchestra Ostrava as Black Pearl. Object Philharmonic has a raw lump of coal situated at Black Meadow site, the former heap. The building is a single mass laceration and shaped by the action of time, relative motion and contact materials are to each other and breaking moves. Tectonics of the facade symbolize brutality material, the piece of coal. On its surface has many different faces, edges, ridges and grooves. It is divided into layers of solid material, opaque and transparent gloss of the opening to the surroundings, providing visual contact with the interior and its interaction with the exterior. Inside, as the energy in coal is burning up, tuned in warm orange tones. It has the power to evoke heat of building, especially at night when during concert. Urban solving a broader relationship Philharmonic building is situated in the area of Black Meadow. The site is in close contact with cents and direct linkage to Masaryk Square. Philharmonic with its position linking a group of cultural objects, which are oriented in Theatre Street. The line begins at the Music Gallery Square, Philharmonic continues to object, bandstand, puppet shows to the theater of Antonin Dvorak. The building is oriented with its longitudinal axis in the direction northeast - southwest. The orientation of the main facade of the north side and is oriented to the Music of the square.