Naval submarines and surface ships are regularly subjected to a treatment called &quotdeperming&quot that seeks to design the vessel???s permanent magnetisation for optimal magnetic camouflage. A scaled model of a magnetic treatment facility (MTF) has been established as a valid system to simulate deperming and used to investigate various aspects of the deperm process including: magnetic anisotropy and demagnetising fields as factors in the physical modelling of magnetism in whole vessels; a comparison of current and alternative deperm procedures; the application of theoretical models of bulk magnetisation to calculate deperm outcomes in the physical model and in actual vessels. A &quotlaboratory MTF&quot was constructed to imitate the applied field geometry at a naval MTF. The system was calibrated and it was determined that the laboratory MTF could make magnetic measurements on a CU200T-G steel bar sample with an equivalent accuracy (error = ??5%) to that of standard magnetometric equipment. Experiments were conducted with emphasis on a holistic approach to modelling the deperm process and describing magnetisation changes in whole objects. The importance of the magnetic anisotropic changes to steel with cold rolling was confirmed. In CU200T-G steel sheet the initial susceptibility (ci) was found to increase by a factor of 3 ??0.1 in the rolling direction, from a value of ~ 110 in the un-rolled steel sheet (thickness dependent). ci in the rolled sheet transverse to the rolling direction was decreased by a factor of 0.94 ??0.09 to ci in the un-rolled sheet steel. Previous studies on hull steel have neglected to account for this transformation through cold work. The demonstration on mild steel here is expected to have an analogy in the final state of the hull sheet steel as it resides in a submarine pressure hull. Future studies either on hull material or on modelling whole vessels should include the same or similar magnetic anisotropic properties in the steel(s) under investigation. Hollow circular tubes made from CA2S-E and CU200T-G steel sheet were selected as models for vessels. It was shown that these steel tubes were a good choice in this regard: minimising the complexity of the experiment whilst maintaining the validity of a deperm simulation. During a deperm there was an excellent qualitative likeness in the permanent longitudinal magnetisation (PLM) for the steel tubes to PLM in both a submarine and a surface vessel. Permanent vertical magnetisation (PVM) deperm results from the tubes displayed a close qualitative match with PVM in a submarine but not in a surface vessel. A theoretical treatment for demagnetisation factors (Nd) in hollow ellipsoids was used in conjunction with a geometrical approximation to calculate Nd for finite hollow objects of revolution. Subsequent theoretical calculations correlated well with experimental results for measured effective ci (ceff) in hollow circular CU200T-G steel tubes of various lengths and aspect ratios. Using an estimate of 100 as ci for submarine hull steel, the same analysis produces Nd for the axial and transaxial directions in a submarine equal to 5.97??10-3 and 0.0142 respectively. Three items for potential improvement were identified in the current deperm protocol used on naval vessels (Flash-D): redundancy in the protocol; the duration of the deperm and a theoretical basis for predicting the final magnetisation or changes in magnetisation during a deperm. Simulations of a novel &quotanhysteretic deperm&quot method, designed to combat these issues, compared favourably to the Flash-D protocol. The standard deviation (s) of the final PVM from 30 Flash-D deperms on steel tubes was 206 A/m; for the final PVM from 30 anhysteretic deperms of the same duration, this was 60 A/m. The s for the final PLM for Flash-D and anhysteretic deperms of the same duration were 416 A/m and 670 A/m respectively. The conclusion is that adopting the anhysteretic deperm on actual vessels would improve the reliability of the PVM outcome. Though the procedure would demand the same duration as Flash-D, there is the advantage of saving time by not having to repeat deperms to obtain the desired result. Additionally the anhysteretic deperm is considerably more amenable to theoretical analysis. A modified version of Langevin???s equation was used to predict the final PLM and PVM results for anhysteretic deperms and to provide a useful analysis of the anhysteretic processes in the Flash-D procedure. Using a Preisach analysis of hysteresis, a mathematical description of bulk magnetic changes that occur to a specific object, within a deperm, has been developed. Theoretical calculations of PLM in a steel tube during and after both types of deperm are in excellent agreement with experimental data. The same theoretical approach was also used to retrospectively model PLM results from previous Flash-D deperms on a submarine with equal success. With this analysis it is proposed that anhysteretic deperm outcomes could be predicted a priori. The influence of magnetic cargo on hull magnetisation was demonstrated to be of significance during and after deperming. &quotSympathetic deperming&quot occurs where a magnetic source is located close to the hull during a deperm. It was found that a vessel or model vessel hull could still be demagnetised even when they contain magnetic cargo that would normally resist the direct application of the same magnetic fields. This was explained using the principles of demagnetising fields and anhysteretic magnetisation. A possible explanation was provided for a PVM measurement anomaly common to the model and vessel deperm results. From measurement, alternating longitudinal applied fields apparently induce corresponding changes in the PVM. This effect could be explained by the depermed object being offset longitudinally from the position expected by the measurement system. This offset could be estimated using an analysis of the changes to PLM and PVM after a longitudinal applied field. The offset displacements calculated for the vessels were too small to be verified experimentally (&gt 0.1m), but the predicted offset for the steel tubes coincided with the limit of precision for their placement in the laboratory MTF = 0.5mm The aim of this work was to look at the deperm process with reference to a system that demonstrated qualitative similarities to deperms on actual vessels. The laboratory MTF is a unique facility, permitting a useful practical analysis of deperming based on sound magnetostatic measurements The experimental and theoretical results gained here have direct application to future deperms on naval vessels with particular reference to submarines.

Quantum phenomena in high-Tc superconductors and dimerized quantum Heisenberg antiferromagnets are studied analytically in this thesis. The implications of the Fermi surface consisting of the disjoint pieces, observed in cuprate superconductors, are considered. It is demonstrated that in this case the g-wave superconducting pairing is closely related to d-wave pairing. The superconductivity in this system can be described in terms of two almost degenerate superconducting condensates. As a result a new spatial scale lg, much larger than the superconducting correlation length x, arises and a new collective excitation corresponding to the relative phase oscillation between condensates, the phason, should exist. The Josephson tunneling for such a two-component system has very special properties. It is shown that the presence of g-wave pairing does not contradict the existing SQUID experimental data on tunneling in the ab-plane. Possible ways to experimentally reveal the g-wave component and the phason in a single tunnel junction, as well as in SQUID experiments, are discussed. The dimerized quantum spin models studied in this thesis include double-layer and alternating chain Heisenberg antiferromagnets. To account for strong correlations between the S=1 elementary excitations (triplets) in the dimerized phase; the analytic Brueckner diagram approach based on a description of the excitations as triplets above a strong-coupling singlet ground state; has been applied. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. Analytical calculations of physical observables are in excellent agreement with numerical data.Results obtained for double layer antiferromagnet near the (zero temperature) quantum critical point coincide with those previously obtained within the nonlinear s model approach Additional singlet (S=0) and triplet (S=1) modes are found as two-particle bound states of the elementary triplets in the Heisenberg chain with frustration.

In this study, we aimed to investigate the magnetic properties of the Co/graphene/Pt(111). Firstly, we used the annealing technique to prepare graphene. The car- bon atoms were segregated from the bulk of the Pt(111) to form graphene eager on the surface. After the preparation of graphene, we confirmed its quality by using STM and LEED. Secondly, we deposited 3 to 25 ML (monolayer) Co on graphene/Pt(111) by electron beam evaporator at low temperature ( 200 K). Then, we measured the ferromagnetic properties of different thickness of Co on graphene / Pt(111) by XMCD, and studied the growth behavior of few monolayer Co on graphene by STM. By serial analysis no ferromagnetic property of few monolayer Co was detected on graphene / Pt(111) by X-ray absorption spectra. The STM image show that the few monolayer Co on graphene mucleates as clusters.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaf 137). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaf 137). Also available on the Internet.

"A modified version of material ... presented as a doctoral dissertation at Harvard University."

The optical and magneto-optical response of plasmonic resonances in metallic nanoarrays out of square structures, either in holes or islands, were investigated. The excitation of the Bragg Plasmons takes place within a grating. Significant differences in the excited plasmon modes were seen by using p- or s-polarized light as well between the holes and islands sample. In order to investigate magneto-optical response from the magnetic nanostrucures, transverse magneto-optical Kerr effect (TMOKE) measurements were done with the result that there is a difference in holes and islands sample. Contrary to what is generally expected for the polarization dependence of TMOKE, a TMOKE signal for s-polarized light on the holes sample was measured.

A new technique is presented for measuring the spatial and momentum distributions of a buffer-gas cooled ion cloud in a Paul trap by extracting it from the trap and fitting the time profile of the extracted ion signal. A thermodynamic model based on the Gibbs distribution has been developed which describes the initial ion cloud phase space volume and fits the measured time distributions of the extracted cloud using only one parameter: temperature. A time-of-flight system has been built to systematically vary the ion extraction conditions and compare predictions of the model to various measurements of the ion cloud time profile. A new numerical method using a multipole expansion was developed to compute the extraction fields. Agreement between the ion simulations and the time-of-flight data is better than 2% of the total flight time. / Ion cloud temperatures were measured for seven different trap loadings of potassium ions and four loadings of sodium ions, in both cases down to clouds of about 1000 ions. This is the first time that temperature measurements have been made for such small numbers of buffer-gas cooled ions. The results show that the temperature of the ions above the buffer gas temperature appears to be proportional to the two-thirds power of the number of ions in the cloud. / Dynamic manipulation of the extracted ion cloud phase space volume was also accomplished using a time-varying acceleration voltage to change the ion cloud energy spread in flight. / A concept is also outlined to measure the detailed phase space area of the extracted cloud using the projection-slice theorem of tomographic imaging. / These measurements have applications for the use of ion traps as beam collectors for nuclear physics experiments at isotope separator facilities and possibly for nano-circuit fabrication.

The detailed observational analysis of three massive B- and O-type stars was carried out in this study in order to characterize their fundamental, magnetic, and variability properties. The bulk of the data acquired were obtained with the high-resolution ESPaDOnS spectropolarimeter at the Canada-France-Hawaii telescope, within the context of the Magnetism in Massive Stars (MiMeS) project. Two of these stars (HR5907 and HD57682) are newly detected magnetic stars, discovered from observations acquired as part of the broader survey component of the MiMeS program, while the last star, ω Ori, was previously reported as magnetic in the literature. The rotation periods of HR5907 and HD57682 were inferred from photometric, Hα emission and longitudinal field variations. A period of 0.508276 was inferred for HR5907, making this the shortest period, non-degenerate, magnetic massive star identified to date. Furthermore, ultraviolet and optical spectroscopy were combined to infer the fundamental properties of HR5907 and HD57682. Direct modelling of the Least-Squares Deconvolved line profiles and the longitudinal magnetic field measurements were used to infer the magnetic properties of HR5907, HD57682, and ω Ori. A detailed investigation of the newly obtained and archival polarimetric data of ω Ori revealed no convincing evidence for a magnetic field, despite evidence of variability in some emission quantities in this dataset, which had been previously attributed to a large-scale magnetic field. The strength and variability of the optical photospheric helium lines of HR5907 suggests that this star is He-rich, with a non-uniform distribution of its surface chemistry. Lastly, the emission variations in the hydrogen lines of HR5907 suggest this star hosts a highly-structured, rigidly-rotating, centrifugally supported magnetosphere. Similarly, line profile variations throughout the optical spectrum of HD57682 are attributed to emission variations caused by a rotationally-modulated, dynamical magnetosphere. As magnetism in massive stars is a relatively rare and poorly-studied phenomenon, these studies comprise the bulk of the detailed investigations of magnetic massive stars carried out to date. The results of these investigations are also discussed in the context of addressing the current outstanding issues related to magnetism in massive stars. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-09-28 17:22:35.115