This thesis covers considerations regarding commercially availble magnetic field sensors and the design work and assembly of a 3-axis magnetic field sensor of Hall technology that is tested for use in a cryostat at the FREIA laboratory, Uppsala university. The assembled sensor needs to withstand cryogenic temperatures and a high vacuum environment. A design for a mechanical structure that will be able to move a matrix of multiple sensors inside the cryostat is also covered. A short section discusses magnetoresistance magnetic field sensors for these purposes. The assembled sensor withstood a cryogenic test and a vacuum test separately, but it did start to show an odd behavior in a specific temperature range towards the last cycles of the cryogenic test. The printed ciruit board didn't show any damage on the board or the solder joints after operation in the vacuum environment.

Bismuth Hall effect sensors with active sizes in the range 0.1µm - 2µm have been fabricated by electron beam lithography and lift-off techniques for applications in scanning Hall probe microscopy (SHPM). The key figures of merit of the sensors have been systematically characterised as a function of device size. The miniumum detectable field of 100nm probes at room temperature is found to be Bmin=0.9mT/Hz0.5, with scope for more than a factor of ten reduction by using higher Hall probe currents. This is significantly lower than in similar samples fabricated by focussed ion beam (FIB) milling of continuous Bi films, suggesting that the elimination of FIB damage and Ga+ ion incorporation through the use of lift-off techniques leads to superior figures of merit. A number of ways in which the T=300K performance of our sensors could be improved still futher are discussed. High resolution scanning Hall probe microscopy (SHPM) with semiconductor 2DEG Hall probe devices has been used to search for novel phases of vortex matter in single crystals of the high temperature superconductor Bi2Sr2CaCu2O8+. In the crossing lattices regime of these highly anisotropic superconductors under tilted magnetic fields two orthogonal types of flux structure are formed known as Josephson and pancake vortices (JVs and PVs). SHPM has been used to study interacting JV-PV matter with very high in-plane fields. The spacing of JV chains has been systematically quantified as a function of both in-plane and out-of-plane fields. Surprisingly, it is found that the JV chain spacing is not solely a function of the in-plane field, as previously assumed, and the effective anisotropy, γ_eff, is shown to depend strongly on the out-of-plane field strength. Moreover, for a fixed in-plane field the JV stack spacing shows pronounced sawtooth-like oscillations as a function of the out-of-plane field. These measurements are giving us unique new insights into the properties of crossing vortex lattices in highly anisotropic cuprate superconductors at high Josephson vortex stack densities.

In this work the interactions between neighboring superconducting thin film and ferromagnetic structures, i.e. superconductor-ferromagnet hybrid systems, were studied. A type-II superconducting thin film (Pb82Bi12), was deposited in close proximity to various ferromagnetic structures. These magnetic structures include: (i) alternating iron-brass shims of 275 mu m period, (ii) an array of 4 mu m wide Co stripes with smaller period (9 mu m), (iii) a square array of 50nm diameter, high aspect ratio (5-7) Ni rods with 250nm period. Measurements of critical transport current (IC), resistance (RH(T)) and second critical field (HC2) are reported. A variety of novel effects (enhancement of (IC) and (HC2), matching field effect, field compensation effect, and large hysteresis) are also reported. Using measurements on thin superconducting films atop a Co stripe array with a 9 mu m period, a superconductor-ferromagnet hybrid device (a mechanical superconducting persistent switch) is proposed. In addition, scanning Hall probe microscopy (SHPM) and other imaging techniques were used to characterize the magnetic properties of the systems mentioned. The SHPM was also used to acquire B-H and M-H curves. An additional sharp magnetic needle and electromagnetic coil assembly intended for micromanipulation of small magnetic particles and individual cells was also characterized.

The high degree of modification through chemical substitution afforded by the perovskite crystal structure and its related counterparts allows a systematic study of structure-property relationships critical to understand the wide variety of exotic phenomena observed in these materials where the spin, charge, orbital, and lattice degrees of freedom are highly correlated. From the multiple phenomena observed in these materials, which includes multiferroicity, catalytic activity, and high temperature superconductivity, this study is concerned with a material that displays colossal magnetoresistance (CMR), La₂₋₂xSr₁₊₂xMn₂O₇; this is a naturally bilayered manganite that exhibits CMR at a paramagnetic to ferromagnetic transition that coincides with an insulator to metal transition. The strong correlation between different degrees of freedom in the material leads to considerable variation in its magnetic properties due to doping even in the small range studied of 0.32 [less than or equal to] x [less than or equal to] 0.4, where the easy axis of magnetization changes from the c-axis to the ab plane. Magnetic force microscopy (MFM) was used for this part of the work, to visualize the local variation of the out of plane (c-axis) magnetization or magnetic microstructure of La₂₋₂xSr₁₊₂xMn₂O₇ for 0.32 [less than or equal to] x [less than or equal to] 0.4 at the exposed ab surface and its evolution due to an applied magnetic field at 4 K. For the x = 0.32 composition, which is close to the out of plane to in plane magnetization transition, a strong preferred magnetization direction within the ab plane or magnetocrystalline anisotropy was observed. The stray magnetic field of the MFM tip perturbs the magnetic microstructure of low coercivity materials like diluted magnetic semiconductors, making it unsuitable for the study of such materials. For this reason, as part of this project a scanning Hall probe microscope (SHPM), a magnetic imaging technique complementary to MFM that uses a Hall sensor that provides a magnetically non-invasive calibrated measurement of the stray fields at the surface of a sample with good resolution (~ 1 [micrometer]), was designed. The construction of a compact cryogenic variable-temperature (77 - 300 K) SHPM, highlighting its features, is described. / text

The purpose of this work is the design of a gaussmeter with a three-axis probe for magnetic field mapping and subsequent reconstruction of the image using magnetic impedance tomography. Commercially available gaussmeters have low bandwidth for these purposes, and signals cannot be measured in synchronous detection mode. The aim of the thesis is select the most suitable magnetic field sensors for the MIT purposes and to design the entire measuring device to meet the measurement requirements in the wider frequency band and synchronous detection. Attention will also be paid to designing a suitable mechanical design of the probe and the location of the sensors. The proposed device will be tested and evaluated for MIT purposes.

This master thesis deals with the design and realization of a drive for a 500 W BLDC motor powered with a battery power supply. It also deals with the possibilities of realization of drives and other possibilities to control these motors. Describes the implementation of the inverter using Atmel's AVR microcontroller. The thesis also deals with the design of an auxiliary switching inverter. Communication with UART and CAN interface is also implemented.

Plus de vingt ans après la découverte de la supraconductivité à haute température critique, le mécanisme physique sous-jacente n'est pas encore bien cerné. En 2008, la découverte d'une nouvelle famille de supraconducteurs à haute température critique, les supraconducteurs à base de fer, a donné l'espoir de trouver une compréhension plus profonde des mécanismes de ce type de supraconductivité. Synthétiser des l'échantillons de grande qualité, la caractérisation des propriétés supraconductrices, l'étude des symétrices du gap et du paramètre d'ordre sont des étapes essentielles pour révéler le mécanisme. La connaissance précise du mécanisme permettra de profiter pleinement des propriétés remarquables de ces matériaux dans leurs applications industrielles si prometteuses. La thèse décrit d'abord la croissance de monocristaux de Ba$_{1-x}$K$_x$Fe$_2$As$_2$ et l'étude de leurs propriétés supraconductrices, menant vers la proposition d'une structure de gap du supraconducteur et d'un paramètre d'ordre pour les supraconducteurs à base de fer Ba-122 à partir de mesures de résistivité, de sondes à effect Hall, de spectroscopie d'Andreev en mode point-contact et de l'imagerie magnétique par la microscopie à nano-squid.Dans le chapitre 1, les événements historiques les plus marquants de la supraconductivité sont rappelés, les propriétés essentielles des supraconducteurs et le dévelopment des théories de la supraconductivité sont esquissés avant de présenter brièvement la découverte des supraconducteurs à base de fer et de donner un aperçu des questions actuelles de recherche dans ce domaine.Dans le chapitre 2, la procédure de croissance de monocristaux de Ba$_{1-x}$K$_x$Fe$_2$As$_2$ par la méthode de "self-flux", leur caractérisation par diffraction et par l'analyse de dispersion d'énergie des rayons X et la sensibilité des mesures de résistivité et de susceptibilité AC sont décrites. Puis nous présentons quelques résultats des mesures de la résistivité dépendante de la température de monocristaux du composé Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (0,23 $\leq x \leq$ 0,4) sous champs magnétiques allant jusqu'à 9 T et dépendante de l'angle.Dans le chapitre 3, nous exposons quelques points essentiels du système de mesure à base de sonde de Hall que nous avons construit. Ensuite, nous présentons des mesures d'aimantation locale et globale sur des polycristaux de SmFeAsO$_{0.9}$F$_{0.1}$ synthétisés à haute pression, et de monocristaux de Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ effectuées par sonde de Hall et VSM.Dans le chapitre 4, nous donnons une brève introduction à la spectroscopie d'Andreev en mode point-contact, puis nous appliquons cette technique à des monocristaux de Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ et à une série de monocristaux de BaFe$_{2-x}$Ni$_x$As$_2$ couvrant une large gamme de dopage.Dans le chapitre 5, le développement d'un microscope de force à nano-SQUID et les mesures effectuées sur un film Rhénium d'épaisseur de 80 nm sont présentés. Le microscope peut acquérir des images topographiques et magnétiques simultanément. La plage de balayage maximale à 0.8 K est de \unit{70} {\micro\meter} $\times$ \unit{85}{\micro\meter} et sa résolution magnétique est d'environ $1,5 \times10^{-4}\Phi_0/\sqrt{\textrm{Hz}}$. Dans le chapitre 6, nous présentons quelques résultats des mesures de $\lambda$ par imagerie par microscopie de force à nano-squid sur des monocristaux de Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$, couvrant tout le diagramme de phase. Sur les m\^{e}mes cristaux ont été effectuées des mesures du premier champ critique, de la variation de fréquence d'un oscillateur à diode tunnel et de la capacité calorifique.Enfin, au chapitre 7, un résumé détaillé et critique est présenté. / More than twenty years after the discovery of high temperature superconductors, the underlying physical mechanism is still not well understood. In 2008, the discovery of a new family of high temperature superconductors, the iron-based superconductors, provided us a new chance to understand the high temperature superconductivity. Synthesizing high quality sample, detecting the basic superconducting properties, the gap structure and order parameter symmetry are essential steps in revealing the mechanism and application of new superconductors. This dissertation describes the growth of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals and the study of superconducting properties, gap structure and order parameter on Ba-122 iron-based superconductors with resistivity, Hall probe, point contact Andreev reflection spectroscopy and scanning nano-squid microscopy measurements. Some historical events concerning superconductivity are recalled, and some key properties and theories of superconductivity are presented in Chapter 1. Then we will briefly introduce the discovery and current research situation of the iron-based superconductors. In Chapter 2, the growth procedure of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals with self-flux method, and the characterization of the crystals with diffraction and energy dispersive analysis of x-ray, AC susceptibility and resistivity measurements are described. Then we report some results from temperature dependent resistivity measurements on Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (0.23 $\leq x \leq$ 0.4) single crystals in magnetic fields up to 9 T and angle dependent resistivity measurements on Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystals. In Chapter 3, we introduce some details about a Hall probe measurement system we built. Then we present local and global magnetization measurements on high pressure SmFeAsO$_{0.9}$F$_{0.1}$ polycrystals and Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystals with Hall probe and VSM.In Chapter 4, we give a brief introduction about point contact Andreev reflection spectroscopy, then we report the measurements on Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystal and a series of electron-doped BaFe$_{2-x}$Ni$_x$As$_2$ single crystals over a wide doping range.In Chapter 5, the development of a scanning nano-SQUID force microscope and measurements performed on a 80 nm Rhenium film are presented. The microscope can take topographic and magnetic images simultaneously. The maximal scanning range is \unit{70}{\micro\meter} $\times$ \unit{85}{\micro\meter} and the magnetic resolution is about $1.5 \times10^{-4}\Phi_0/\sqrt{\textrm{Hz}}$. In Chapter 6, we present some results from lower critical field, tunnel diode oscillator, heat capacity and scanning nano-squid microscopy measurements on systematic doped Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ single crystals..Finally, in Chapter 7, a detailed summary is presented.

The work describes the design and implementation of compact inverter for brushless DC motor, which have mechanical power 600 W and rated torque 1.6 Nm. Motor is designed for DC link voltage with value 300 V. The focus is placed on the cost and simplicity. On this basis, the inverter is designed for uses single purpose power and control circuit. The power part is solved using a circuit FSBB15CH60C. The circuit is placed on a separate board of power electronics. Cooling of the power circuit is performed by the surface structure of BLDC motor. Control of the inverter ensures circuits LB11696V and NE566. The both circuits are placed on separate board of control electronics. Circuit LB11696V contains a control algorithm, as well as protections, which are necessary for safe operation of the inverter. Power supply of electronics is performed using step-down converter from MYRRA company.

The most commonly known macro scale probing devices are simply comprised of metallic leads used for measuring electrical signals. On the other hand, micromachined probing devices are realized using microfabrication techniques and are capable of providing very fine, micro/nano scale interaction with matter; along with a broad range of applications made possible by incorporating MEMS sensing and actuation techniques. Micromachined probes consist of a well-defined tip structure that determines the interaction space, and a transduction mechanism that could be used for sensing a change, imparting external stimuli or manipulating matter. Several micromachined probes intended for biological and nanotechnology applications were fabricated, characterized and tested. Probes were developed under two major categories. The first category consists of Micro Electromagnetic Probes for biological applications such as single cell, particle, droplet manipulation and neuron stimulation applications; whereas the second category targets novel Scanning Probe topologies suitable for direct nanopatterning, variable resolution scanning probe/dip-pen nanolithography, and biomechanics applications. The functionality and versatility of micromachined probes for a broad range of micro and nanotechnology applications is successfully demonstrated throughout the five different probes/applications that were studied. It is believed that, the unique advantages of precise positioning capability, confinement of interaction as determined by the probe tip geometry, and special sensor/actuator mechanisms incorporated through MEMS technologies will render micromachined probes as indispensable tools for microsystems and nanotechnology studies.

The master thesis encompasses the possibilities of position evaluation and drive control with the aid of SMI work enviroment. Furthermore the thesis is directed to create a program through a designed control algorithm. The work is realised on the elevator model with electronically commuted motor. An incremental scanner is used as the position sensor. The motor control unit is set up and programmed in the SmartMotorInterface software. In the next part, measurements with altered parameters are conducted. On the basis of these measurements the influence of parameters on the positioning process and its accuracy is evaluated. At the conclusion of the work, a design of laboratory task for educational purposes is created. The laboratory task is composed in such a way, that students would become familiar with the SMI work enviroment and would be able to practicaly test the setup of incremental position sensor and motor control with the aid of entered algorithm.