This thesis describes the development of a new type of Magnetic Force Microscope (MFM) probe based on a unique electromagnetic design. In addition the design, construction and testing of a new MFM system, complete in both hardware and software, is also described. The MFM allowed initial tests on prototypes of the new probe, and is to provide a base for future new probe integration. The microscope uses standard MFM micro-cantilever probes in static modes of imaging. A new computer hosted DSP control system, software, and its various interfaces with the MFM have been integrated into the system. The system has been tested using standard probes with various specimens and satisfactory results have been produced. A novel probe has been designed to replace the standard MFM magnetic coated tip with a field generated about a sub-micron aperture in a conducting film. The field from the new probe is modelled and its imaging capability investigated, with iterative designs analysed in this way. The practical construction and potential problems therein, of the probe are also considered. Test apertures have been manufactured, and an image of the field produced when operating is provided as support to the theoretical designs. Future methods of using the new probe are also discussed, including the examination of the probe as a magnetic write mechanism. This probe, integrated into the MFM, can provide a new method of microscopic magnetic imaging, and in addition opens a new potential method of magnetic storage that will require further research.

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Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains x, 63 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 62-63).

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains x, 81, 9 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 73-75).

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The thesis is mainly focused on the investigation of macroscopic and microscopic magnetic properties of selected nanomaterials containing cobalt and iron, and also the capability of our new device, scanning probe microscope Multimode V by Veeco, to directly visualise morphology and magnetic structure of these samples (Magnetic Force Miscroscopy, MFM). Investigated materials, such as CoFe2O4 nanoparticles and SiO2_Co_Si(111) thin films and multilayers are in general promising materials in many fields. In the medicine, the nanoparticles are used as the drug targets or contrast agents whereas in electronics, the (nano)granular thin films are the starting point in fabrication of high density storage media. The macroscopic magnetic properties of our samples are discusses in a view of superparamagnetic phenomena. The interactions in systems of nanoparticles are presented theoretically within the up-to date knowledge and also experimentally by demonstrating the behavior of the strongly-interacting, uper-spin-glass system. The thin films are studied in term of their granular structure and magnetic anisotropy. The morphology and the microscopic domain structure, respectively, are studied with use of the MFM. The first successful results obtained in our lab by this method are presented.

High-quality silicon crystals provide the basis of many industrial technological advances, including computers and telecommunication devices. The increasing size and extremely high quality requirements of silicon wafers have made furnace design and crystal manufacturing a very challenging task. Numerical simulations have become an essential and powerful tool to overcome the difficulties of the experimental approach with a view to understanding the crystal growth process but also to finding an appropriate path to optimize the crystal pulling conditions in industry.</br></br> This thesis deals with the use of alternating and steady transverse magnetic fields in silicon growth from the melt. The use of magnetic fields represents a powerful tool to damp out turbulence and control the melt flow. This technique can also be used to heat the system. We focus on the numerical modeling of (i) induction heating in the Floating Zone process and of (ii) melt convection under the effect of transverse magnetic fields in the Czochralski process. For each of these topics, our work is subdivided in two parts : firstly mathematical modeling, based on asymptotic or Fourier expansions, and secondly numerical implementation and simulation of the considered processes. </br></br> First, a theoretical and numerical model of the alternating magnetic field distribution (as generated by induction heating) has been developed by means of an asymptotic expansion technique. Moreover, a new methodology has been developed to calculate the thermal and mechanical effects of alternating magnetic fields on the liquid conductor flow, leading to accurate expressions for the equivalent magnetic heat flux and surface stresses in the 2D and 3D cases. Second, investigation of the effect of a transverse magnetic field on the melt flow in semi-conductor crystal growth has been performed by the simplified FLET method (“Fourier Limited Expansion Technique”.)

This thesis examines the dynamics of the formation of tethers, which are tubes of lipids 20 - 200 nm in diameter. In particular, this work investigates how the loading rate affects the observed threshold force at which a tether forms from a vesicle membrane. Tether dynamics are important to a myriad of biological processes such as signaling when white blood cells adhere to the walls of healthy and diseased blood vessels, or in the transport of intracellular material between neighboring cells. To understand the dynamics of tether formation in such systems more fully, the studies presented in this thesis focus on the dependence of the force needed to create a tether on the rate of force change. To conduct these experiments, I combined, for the first time, a microfabricated magnetic force transducer, or a microscale device that generates well-controlled and localized magnetic fields, and microaspiration, a technique to apply known tension to a lipid membrane. Using the combined global and local mechanical control of the joint system, I discovered a strong correlation between the threshold force of tether formation and the applied force ramp. An energy model, based upon that used to describe membrane rupture, characterized the observed dependencies and provided a mechanism to examine physically relevant quantities within the system. The usefulness of this combined approach was further substantiated by determining the influence of membrane modulators, including cholesterol, tension, adhesion site concentration, and phosphatidylserine, on the dependence seen between force threshold and force rates. Additionally, application of the experimental technique developed in this thesis led to the calculation of the inter-layer drag coefficient between membrane leaflets and to the first measurements of the thermal expansivity in aspirated 1-stearoy1-2-oleoyl- sn -glycero-3-phosphatidylcholine vesicles. This new tool for dynamic studies of membrane mechanics may further be extended to study how tethers form off of flowing cells or how phase regimes, induced by the presence of cholesterol, influence membrane dynamics.

This dissertation is divided into two parts. In the first, the general paradigm of scanned probe microscopy is outlined with a focus on atomic force microscopy and a few of its variations. Magnetic force microscopy is covered in detail as it forms the basis of the second part of this dissertation. The core elements and extra features of the instrument are described with attention paid to the upgrades made by the author. In the second part of this dissertation, background information on perovskite oxides and the inverse spinel system, magnetite, is given. Magnetic force microscopy studies were done on three thin film systems and are detailed. In the first study, ferromagnetic manganite films were subjected to discontinuous changes in strain due to structural transitions in their barium titanate substrates. The resulting effect on the magnetic domains was observed. In the second study, the ferromagnetism of a tensile-strained LaCoO₃ film was studied across temperatures from 4.3 K to 90 K and applied fields up to [mu]₀H=1.1 T. Finally, the properties of antiphase domains in magnetite films of varying film strain due to transition metal buffer layers was probed by imaging the magnetic domains which are pinned to the antiphase boundaries. / text

Eddy current separation aims to recover non-ferrous metals from non-metals utilizing electromagnetic interactions. In order to describe the separation process, a representative model is needed that can accurately calculate the induced forces. Such a model can be used to optimize the efficiency of current equipment as well as designing ones that can offer new capabilities. Models proposed so far for the separation process, using traditional approaches to calculate forces, had limited success due to complex nature of electromagnetic interactions. In this dissertation, a novel method for calculating the magnetic force acting on non-ferrous metal particles was developed. By this method, force calculations can be carried out accurately using intrinsic parameters of particles such as size and shape, as well as its orientation within the field. The method also takes into account the operating parameters of the equipment such as the rotational speed of the magnetic element and the speed of the belt. In order to verify this method and collect empirical data, a novel data acquisition and interpretation approach was developed. A computer simulator was also developed that can calculate trajectories of particles based on operating parameters of the eddy current separator and characteristics of the material being processed. The accuracy of the simulator was verified using empirical data obtained by the novel data acquisition method. This contribution provides a viable option for reducing the cost of analyzing; optimizing and designing eddy current separators. / PHD