Ferromagnetism (FM) and superconductivity (SC) are traditionally thought of as competing states of matter, since the opposite-spin electron pairing mechanism required for conventional SC is rendered impossible by FM spin alignment. However, recently discovered heavy-fermion compounds UGe2 and URhGe are examples where SC and FM are cooperative, and rather than antagonistic the presence of FM is actually necessary for the occurrence of the SC phase. A cooperative state of FM and SC is a topic of interest because it presents a possible solution to one of the two main problems with present superconductors: technology inhibiting limits on the highest temperature and highest magnetic field to which the SC phase can exist. Although both UGe2 and URhGe cease to be superconductors before even reaching 1 K, unlike the various `high temperature' superconductors currently known that easily surpass 100 K, it is their magnetic properties that are interesting, the inherent FM ordering allowing them to exceed conventional limits on the maximum magnetic field that SC can withstand. For example, URhGe remains superconducting above 35 T and the upper limit is so high that it is still experimentally undetermined. How exactly the FM SC phase arises in these compounds is as yet unknown. The necessary opposite-spin pairing mechanism is theoretically provided by magnetic fluctuations in an easily polarizable system right on the edge of a magnetic phase transition, and indeed SC emerges in UGe2 and URhGe around a first-order quantum critical point (QCP) where the temperature of the transition to an FM phase is reduced to absolute zero, by application of pressure in the case of UGe2 and by application of a magnetic field for URhGe. The aim of the research detailed in this thesis is to probe the FM phase transition and the associated QCP related to the emergence of SC in these compounds, to gather more information about the precise nature of the phases either side of the transition and exactly what changes occur in the system crossing the QCP. Specifically, the main objective is to characterise the magnetic fluctuations at the phase boundary and determine whether, by current FM SC theory, these fluctuations could be responsible for SC or if instead other, modified, unconventional theories are required to explain the unconventional electron pairing. The probes of choice for this PhD were Hall effect and magnetoresistance measurements of UGe2, and capacitive torque magnetometry and simultaneous magnetoresistance measurements of URhGe. The main result of the UGe2 project is an observed order-of-magnitude change in the Hall coefficient crossing the FM transition as a function of temperature and a dramatic change, similar in magnitude but also accompanied by a sign reversal, crossing the QCP as a function of pressure. Furthermore, the sign reversal at the critical pressure persists up to roughly 12 K, far beyond the 7 K critical end point of the phase transition, suggesting that in fact three different phases converge at the QCP where fluctuations between them presumably lead to the emergence of SC. Further investigation of the Fermi surface, either by deeper analysis of the Hall effect results or by other experimental methods, will be required to complete the main objective and determine exactly what the differences are between these newly identified phases. The main result of the URhGe project is actually the successful development of the capacitive torque magnetometry technique itself and the proof of operation for simultaneous measurement of all the individual components of both the magnetization and differential susceptibility tensors in a high magnetic field, which is currently not possible by any other technique. Completing the main objective was hampered by the extremely high susceptibility components encountered in the vicinity of the QCP, which in itself could be considered evidence for the theoretical relationship between strong FM fluctuations and the emergence of SC in URhGe. A number of results incidental to the main aim of the URhGe project are also summarised in this thesis, including the characterisation of quantum oscillations frequencies not previously reported in scientific literature and a variety of subtle features in resistivity measurements, which could, in conjunction with evidence from the susceptibility measurements, suggest the presence of another superconducting state such as surface or domain wall SC.

This dissertation focuses on two connected areas: quantum computation and quantum control. Two proposals to construct a quantum computer, using nuclear magnetic resonance (NMR) and superconductivity, are introduced. We give details about the modeling, qubit realization, one and two qubit gates and measurement in the language that mathematicians can understand and fill gaps in the original literatures. Two experimental examples using liquid NMR are also presented. Then we proceed to investigate an example of quantum control, that of a magnetometer using quantum feedback. Previous research has shown that feedback makes the measurement robust to an unknown parameter, the number of atoms involved, with the assumption that the feedback is noise free. To evaluate the effect of the feedback noise, we extend the original model by an input noise term. We then compute the steady state performance of the Kalman filter for both the closed-loop and open-loop cases and retrieve the estimation error variances. The results are compared and criteria for evaluating the effects of input noise are obtained. Computations and simulations show that the level of input noise affects the measurement by changing the region where closed loop feedback is beneficial.

Made available in DSpace on 2016-01-13T13:27:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-03-15. Added 1 bitstream(s) on 2016-01-13T13:33:00Z : No. of bitstreams: 1 000855254.pdf: 5885285 bytes, checksum: b3fd3d0ee13e84e2b552976e5ddcba21 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Esse trabalho consiste na aquisição de dados de magnetometria terrestre numa área compreendida por duas ocorrências cupríferas denominadas Capão Grande e Victor Teixeira, localizadas no interior do município de Caçapava do Sul-RS. Os dados resultantes da aplicação desse método geofísico foram adquiridos com o propósito de caracterizar a subsuperfície para verificar uma potencial relação de conexão entre as mineralizações dessas ocorrências de cobre. A ocorrência Capão Grande tem como encaixante as rochas sedimentares da Bacia do Camaquã. Já a ocorrência Victor Teixeira está inserida em rochas metamórficas do Escudo Sul-Rio- Grandense. Na caracterização de subsuperfície foram empregados levantamentos de medidas de intensidade do campo magnético total ao longo de perfis e sob a forma de malha no intervalo de 2300 m entre as ocorrências mineralizadas. Essas medidas foram processadas em conjunto, e os produtos resultantes foram os mapas do campo magnético total, passa banda profundo, passa banda raso e amplitude do sinal analítico. Análises e discussões posteriores desses mapas com a sobreposição das principais informações geológicas da área e de resultados geofísicos de interesse de estudos anteriores permitiram a definição de que as mineralizações das ocorrências estudadas não apresentam conexão em subsuperfície / This paper consists of the acquisition of terrestrial magnetometry data in an area comprised of two mineralized occurrences copper called Capão Grande and Victor Teixeira, located in the city of Caçapava do Sul, in the south of Brasil. The resulting data from the application of this geophysical method characterizing the subsurface to check a potential connection relationship between these copper mineralization occurrences. The Capão Grande occurrence has the enclosing sedimentary rocks of the Camaquã Basin. Victor Teixeira occurrence is inserted into metamorphic rocks Sul-Rio-Grandense Shield. In characterizing subsurface magnetic surveys were employed intensity of the total magnetic filed measurements along the profiles and in the form of mesh in the of 2300 m between the mineralized occurrences. These measurements were processed together, and the products resulting were, the total field maps, band pass deep, band pass shallow, and the analytic signal amplitud. Analysis and further discussion of these maps with the overlay of the main geological information of the area and geophysical results of interest from previous studies allowed the definition of the mineralization of the cases studied show no connection in the subsurface

Submitted by LENON MELO ILHA null (lenonilha@unipampa.edu.br) on 2017-08-22T14:11:00Z No. of bitstreams: 1 Levantamento Magnetométrico em Sequência Metaultramáfica Mineralizada em Cromita, São Sepé (RS).pdf: 4941337 bytes, checksum: 4bae6be70b020d210ee384046ccfeadd (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-08-23T18:49:11Z (GMT) No. of bitstreams: 1 ilha_lm_me_rcla.pdf: 4941337 bytes, checksum: 4bae6be70b020d210ee384046ccfeadd (MD5) / Made available in DSpace on 2017-08-23T18:49:11Z (GMT). No. of bitstreams: 1 ilha_lm_me_rcla.pdf: 4941337 bytes, checksum: 4bae6be70b020d210ee384046ccfeadd (MD5) Previous issue date: 2017-06-30 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Estudos de prospecção e pesquisa mineral por meio da geofísica são fundamentais para o reconhecimento e incorporação de novas reservas, devido ao baixo custo em relação aos métodos diretos de investigação e a possibilidade de cobertura de amplas áreas. Este trabalho consiste na aplicação do método da Magnetometria Terrestre, na caracterização de um corpo ultramáfico metamorfizado e mineralizado em cromo, a área de estudo se localiza na zona rural do município de São Sepé (RS) e situada nos limites das rochas do Escudo Sul Riograndense. Os litotipos presentes na área são arenitos, rochas metavulcânicas e rochas máficas/ultramáficas. Foram realizadas 1677 leituras em linhas perpendiculares a direção principal do corpo ultramáfico, com espaçamento de 25 metros entre pontos de medida. Os mapas magnetométricos gerados revelam anomalias de alta intensidade, acima de 420nT no mapa de intensidade de campo total, relacionadas com as rochas ultramáficas. Os resultados demonstraram a aplicabilidade do método da magnetometria na individualização de ocorrências minerais magnéticas de dimensões métricas, e a possibilidade de uso na seleção de alvos para perfuração, amostragem e quantificação de teores, em rotinas de pesquisas por depósitos de cromo. / Studies of mineral research and exploration through geophysics are fundamental for the recognition and incorporation of new reserves, due to the low cost in relation to the direct methods of investigation and the possibility of covering large areas. This work consists of the application of the Terrestrial Magnetometry method, in the characterization of a metamorphic and mineralized chrome mineralized body, the study area is located in the rural area of the city of São Sepé (RS) and located in the limits of the rocks of the Escudo Sul Riograndense. The lithotypes present in the area are sandstones, metavulcanic rocks and mafic / ultramafic rocks. There were 1677 readings in lines perpendicular to the main direction of the ultramafic body, with spacing of 25 meters between measurement points. The generated magnetometric maps show high intensity anomalies, above 420nT in the map of total field strength, related to ultramafic rocks. The results demonstrated the applicability of the magnetometry method in the individualization of magnetic mineral occurrences of metric dimensions, and the possibility of use in the selection of targets for drilling, sampling and quantification of contents, in search routines for chromium deposits. / CNPq: 470821/2013

Orientador: Walter Malagutti Filho / Banca: César Augusto Moreira / Banca: Maximilian Fries / Resumo: Esse trabalho consiste na aquisição de dados de magnetometria terrestre numa área compreendida por duas ocorrências cupríferas denominadas Capão Grande e Victor Teixeira, localizadas no interior do município de Caçapava do Sul-RS. Os dados resultantes da aplicação desse método geofísico foram adquiridos com o propósito de caracterizar a subsuperfície para verificar uma potencial relação de conexão entre as mineralizações dessas ocorrências de cobre. A ocorrência Capão Grande tem como encaixante as rochas sedimentares da Bacia do Camaquã. Já a ocorrência Victor Teixeira está inserida em rochas metamórficas do Escudo Sul-Rio- Grandense. Na caracterização de subsuperfície foram empregados levantamentos de medidas de intensidade do campo magnético total ao longo de perfis e sob a forma de malha no intervalo de 2300 m entre as ocorrências mineralizadas. Essas medidas foram processadas em conjunto, e os produtos resultantes foram os mapas do campo magnético total, passa banda profundo, passa banda raso e amplitude do sinal analítico. Análises e discussões posteriores desses mapas com a sobreposição das principais informações geológicas da área e de resultados geofísicos de interesse de estudos anteriores permitiram a definição de que as mineralizações das ocorrências estudadas não apresentam conexão em subsuperfície / Abstract: This paper consists of the acquisition of terrestrial magnetometry data in an area comprised of two mineralized occurrences copper called Capão Grande and Victor Teixeira, located in the city of Caçapava do Sul, in the south of Brasil. The resulting data from the application of this geophysical method characterizing the subsurface to check a potential connection relationship between these copper mineralization occurrences. The Capão Grande occurrence has the enclosing sedimentary rocks of the Camaquã Basin. Victor Teixeira occurrence is inserted into metamorphic rocks Sul-Rio-Grandense Shield. In characterizing subsurface magnetic surveys were employed intensity of the total magnetic filed measurements along the profiles and in the form of mesh in the of 2300 m between the mineralized occurrences. These measurements were processed together, and the products resulting were, the total field maps, band pass deep, band pass shallow, and the analytic signal amplitud. Analysis and further discussion of these maps with the overlay of the main geological information of the area and geophysical results of interest from previous studies allowed the definition of the mineralization of the cases studied show no connection in the subsurface / Mestre

Geophysical surveys in the Republic of Ireland and elsewhere rarely have the opportunity to receive direct, meaningful and quantitative feedback from ground observed excavations, despite their frequent occurrence as a subsequent phase of development-led archaeological projects. This research critically reappraises the largest and most coherent geophysical archive maintained by a single end-user over a ten year period. The geophysical archive has been collated from 170 reports on linear road schemes as a result of commercially-driven assessments in Ireland, to facilitate the biggest analysis of geophysical survey legacy data and subsequent detailed excavations. The analysis of the legacy data archive has reviewed and tested the influence of key variables that have, in some circumstances, affected the methods and outcomes of geophysical assessments in Ireland over the last 10 years. By understanding the impact of those key variables upon the legacy data - which include archaeological feature type, geology, sampling strategy and seasonality - appropriate and new ways to research linear corridors have been suggested that should be employed in future geophysical survey assessments for a range of environments and archaeological site types. The comprehensive analysis of geophysical surveys from the legacy data archive has created definitive statements regarding the validity of geophysical techniques in Ireland. Key failures that occurred in the past have been identified and a thorough investigation of new and novel techniques or methods of survey will facilitate a more robust approach to geophysical survey strategies in the future. The outcomes of this research are likely to have ramifications beyond the Irish road corridors from which the legacy data derives. / National Roads Authority (NRA)

<p>With the advances in MEMS technology, the studies of the properties of magnetic crystals have reached the microscopic level. Critical information such as the magnetization and susceptibility of a magnetic sample can be obtained using a microtorque magnetometer, such as ones incorporating piezoresistive or capacitive detection that have been fabricated and tested by earlier research groups. This type of magnetic information is useful in the study of superconductivity, for example. The microtorque magnetometer designed and fabricated in this thesis has the potential of being used in this field of study.</p> <p>This thesis describes the design, fabrication and testing of a capacitive microtorque magnetometer. By using ANSYS, a computer modelling program, an ideal model of the rotating microtorque magnetometer was devised. Fabrication involved testing a variety of procedures before establishing the successful and efficient method of building the microtorque magnetometer. A fifth order resonant mode was successfully detected during the testing stage. A method of studying the desired resonant mode has been devised and explained in the later chapters of this thesis.</p> / Master of Applied Science (MASc)

No

L'imagerie de champs magnétiques de faible amplitude avec une résolution spatiale à l'échelle nanométrique est un enjeu important dans de nombreux domaines de la physique et pour de multiples applications, que ce soit par exemple en science des matériaux pour le stockage magnétique de l'information, ou bien en optique quantique afin de pouvoir contrôler un spin individuel utilisé comme bit quantique, ou encore en biophysique pour l'étude structurelle de protéines par résonance magnétique. Dans ce contexte, cette thèse décrit la réalisation d'un magnétomètre à balayage fondé sur la réponse magnétique du spin électronique d'un centre coloré NV du diamant. Un tel magnétomètre présente des propriétés sans équivalent, en combinant une résolution spatiale sub-nanométrique, assurée par la dimension atomique du capteur, et une très haute sensibilité (< 1 µT/Hz^(-1/2)), ceci même à température ambiante. De plus la mesure de champ magnétique est quantitative et non perturbative, offrant ainsi un avantage majeur par rapport à la microscopie à force magnétique couramment utilisée pour l'imagerie magnétique de nanostructures. Nous aborderons, dans un premier temps, les problématiques liées à la fabrication de la sonde magnétique, constituée par un centre coloré NV unique dans un nanocristal de diamant positionné à l'extrémité d'une pointe AFM. Les propriétés de ce magnétomètre seront caractérisées en imageant le champ de fuite d'un disque dur magnétique. Cette étude nous permettra d'introduire différentes méthodes d'imagerie magnétique et de comparer leurs performances. Le magnétomètre à centre NV sera par la suite utilisé pour imager des distributions d'aimantation vortex dans des plots ferromagnétiques, dont le cœur est connu pour être l'un des objets les plus petits du micromagnétisme, le rendant extrêmement difficile à observer. Les propriétés du magnétomètre à centre coloré NV du diamant, démontrées dans cette thèse, ouvrent la voie à de nombreuse études en nanomagnétisme et en spintronique. / Imaging weak magnetic fields at the nanoscale is a challenge for many field of reasearch, and for a wide range of applications, such as in material science, for the magnetic storage of the information, or in quantum optics with the opportunity to control a single spin used as a quantum bit, or in biophysics where magnetic resonance can enable structural imaging of a protein. In that context, this thesis describes the realisation of a scanning probe magnetometer based on the electron spin resonance of a single NV colour centre in diamond. Such a magnetometer provides unprecedented properties, consisting of a sub-nanometric spatial resolution, given by the effective atomic size of the defect, combined with a high sensitivity (< 1 µT/Hz^(-1/2)), even at room temperature. Moreover magnetic field ca be measured quantitatively, with no perturbation induced, which is a major asset comparing to what can be done using the usual magnetic force microscopy technique. We will first describe the realisation of the magnetic probe, consisting of a single NV colour centre in a diamond nanocristal, grafted at the apex of an AFM tip. Properties of this magnetometer will be then characterized by imaging the stray field generated by a magnetic hard disk. Different imaging techniques will be presented, and compared during this study. Finally, magnetic vortex in patterned ferromagnetic thin film will be imaged, especially the vortex core, which is known to be one of the smallest object of micromagnetism. The exceptional properties of NV based magnetometry, demonstrated in ths work, might enable various applications in nanomagnetisms and spintronics.

Geophysical surveys in the Republic of Ireland and elsewhere rarely have the opportunity to receive direct, meaningful and quantitative feedback from ground observed excavations, despite their frequent occurrence as a subsequent phase of development-led archaeological projects. This research critically reappraises the largest and most coherent geophysical archive maintained by a single end-user over a ten year period. The geophysical archive has been collated from 170 reports on linear road schemes as a result of commercially-driven assessments in Ireland, to facilitate the biggest analysis of geophysical survey legacy data and subsequent detailed excavations. The analysis of the legacy data archive has reviewed and tested the influence of key variables that have, in some circumstances, affected the methods and outcomes of geophysical assessments in Ireland over the last 10 years. By understanding the impact of those key variables upon the legacy data - which include archaeological feature type, geology, sampling strategy and seasonality - appropriate and new ways to research linear corridors have been suggested that should be employed in future geophysical survey assessments for a range of environments and archaeological site types. The comprehensive analysis of geophysical surveys from the legacy data archive has created definitive statements regarding the validity of geophysical techniques in Ireland. Key failures that occurred in the past have been identified and a thorough investigation of new and novel techniques or methods of survey will facilitate a more robust approach to geophysical survey strategies in the future. The outcomes of this research are likely to have ramifications beyond the Irish road corridors from which the legacy data derives.