The morphology, composition, and magnetic properties of NiFe thin films were characterized. Films with thicknesses up to 137 nm were deposited in an RF induction evaporator at high vacuum (10^-8 mbar). Time resolved magneto-optic Kerr effect microscopy (TR-MOKE) was used to measure the Gilbert damping constant, an important dynamic magnetic property with applications to magnetic data storage. The composition of each film was measured with energy-dispersive X-ray (EDX) microscopy and used to determine the weight percent of Ni and Fe in each film. A trend of increased damping with increased thickness was found, in agreement with published results. Magnetic properties and roughness were found to differ significantly from previous films grown in the same vacuum chamber by Rudge, and are attributed to different growth modes produced by differing deposition conditions. However, the weight percent of Ni in each film was found to be inconsistent, deviating by up to 7% from the Ni80Fe20 evaporation source. Inconsistent composition, caused by the inability to control deposition parameters, prevents insight into Gilbert damping from being drawn from the analysis. / Graduate

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references (leaves 145-148). Issued in print and online. Available via ProQuest Digital Dissertations.

Title from first page of PDF document. Includes bibliographical references (p. 62-63).

Le processus de filamentation découle de la balance dynamique de plusieurs effets linéaires et non-linéaires, permettant l'auto-stabilisation du faisceau laser sur des distances de propagation significativement supérieures à celles prédites par la théorie des faisceaux gaussiens. Cette thèse s'attache à décrire ce phénomène dans les gaz rares en modèle dit de champ fort, par opposition au modèle usuel, utilisé dans le cadre de la théorie des perturbations et s'appuyant sur l'approximation du champ faible. L'influence des harmoniques, jusqu'ici négligée, est alors revisitée tant au niveau microscopique qu'à l'échelle d'une propagation. Il est montré, expérimentalement et par l'appui de simulations numériques, qu'il suffit d'une faible proportion de troisième harmonique pour que la dynamique de la filamentation soit fortement impactée, notamment à travers le processus d'ionisation. Egalement, la proximité d'une résonance peut mener à de fortes modifications du mécanisme d'auto-guidage: lorsqu'un champ fondamental centré à 400nm et sa troisième harmonique interagissent avec du krypton, il est montré que le processus de modulation de phase croisée est renforcé et qu'il peut alors endosser un rôle défocalisant de manière non-négligeable. Une autre situation - à 300nm dans le krypton - amène à un renforcement résonant de la filamentation, se traduisant par l'allongement de la longueur du filament par rapport au cas hors-résonance. / Filamentation originates from the dynamic balance between linear and nonlinear effects, allowing the laser beam autostabilization over distances significantly greater than those predicted by linear optics laws. The aim of this thesis is to describe this phenomenon on rare gases under the strong field model, contrary to the commonly used perturbation model based on the weak field approximation. The influence of harmonics, so far neglected, is then revisited both at the microscopic level and at a propagation scale. It is shown, experimentally and with the support of numerical simulations, that a weak proportion of third harmonic is sufficient to strongly impact the filamentation dynamics, especially through the ionization process. Also, the vicinity of a resonance can lead to strong modifications of the self-guiding mechanism: when a fundamental field centered at 400nm and its third harmonic interact together with krypton, it is shown that the cross-phase modulation process is enhanced and can participate to the beam defocusing. Another situation - at 300nm in krypton - leads to resonantly enhanced filamentation, i.e. to longer filaments compared to the non-resonant case.

The Kerr effect is the rotation of the plane of polarization of a light beam during reflection on a magnetized sample. In this work we built an optical Kerr effect magnetometer Longitudinal (L-MOKE) and measured the magnetization of thin films produced by the technique of "magnetron sputtering". The magnetization measurements were in samples of permalloy (Py), iron (Fe) and a tri-layer Py/IrMn/Ta. / O efeito Kerr consiste na rotação do plano de polarização de um feixe de luz durante a reflexão sobre uma amostra magnetizada. Neste trabalho construímos um magnetômetro ótico de efeito Kerr Longitudinal (L-MOKE) e realizamos medidas de magnetização de filmes finos produzidos pela técnica de magnetron sputtering . Foram realizadas medidas de magnetização com amostras de permalloy (Py), ferro (Fe) e uma tri-camada de Py/IrMn/Ta.

The transient electric birefringence method, i. e. the transient Kerr effect, has been employed to study the optical, electrical and geometrical properties of three macromolecular systems. An apparatus is described in which the birefringence could be measured when d. c. electric field pulses (of duration 1μs to 5s and strength up to 50 KV/cm) and a. c. electric field pulses (of duration greater than 5 ms, of frequency up to 20 kHz, and strength up to 3 KV/Cm) were applied to solutions of macromolecules. Both the linear and quadratic optical systems have been employed to measure the induced birefringence. A theoretical analysis and review of the errors implicit in such measurements is given, with suggested alignment and calibration procedures. For the first time in electro-optic work, a data-logging system and computer program have been developed and employed, and enabled the automatic recording of transient responses with subsequent high speed data analysis. Measurements have been made on a polypeptide poly – β – benzyl – 1 – aspartate in two solvents. These show how the method can be used to study a rigid macromolecule. A novel investigation was made on the interaction of an anionic surfactant, sodium dodecyl sulphate, with a flexible polymer, polyvinylpyrrolidone. The large variation of Kerr constant observed with addition of surfactant indicated a great potential use of this method for studying polymer surfactant interactions. An aqueous suspension of the bacteria E. coli was also studied, but changes in turbidity and not birefringence were the origin of the observed effects. Novel practical methods of investigation, and turbidity calculations carried out with the aid of a computer enabled size parameters and electrical properties to be determined for E. coli. For the first time such results were in agreement with electro-optic light scattering measurements.

Liquid crystals are a vast and diverse class of materials which ranges from fluids made up of simple rods, polymers and solutions, to elastomers and biological organisms. Liquid crystal phases are neither crystalline, nor a ‘normal’ isotropic liquid, but lie somewhere in between these two common states of matter. Liquid crystals have found enormous use in display devices due to their electro-optic properties. In this thesis, the optical and electro-optical properties of some chiral liquid crystalline phases are studied. The optical and electro-optical behaviour of liquid crystalline blue phases has been investigated via a detailed analysis of the reflection spectrum from thin, vertical field (VF) cells. Spectral analysis in this thesis was performed using a numerical fitting technique based on the Berreman 4x4 matrix method. The validity of the technique was proved through comparisons of independent measurements with the calculated physical parameters. A novel Kerr effect measurement method was proposed in this thesis and a known material was used to verify this new method. The Kerr constant together with its dispersion relation was measured using a white light source. An unusually large Kerr constant, K, is determined in the blue phases of a non-polymer stabilized material, ~ 3x10-9 mV-2 (BPI). The large value of K is attributed to significant pre-transitional values of the dielectric anisotropy and birefringence. K follows an inverse dependence on temperature which is more marked in BPII than BPI, and we consequently suggest that the BPI demonstrates properties best suited to electro-optic devices. The field effects in blue phase include electrostriction and the influence of the Kerr effect was separated from electrostriction phenomena for the first time in this work. Finally in the Kerr effect measurements, the Kerr constant in the optically isotropic dark conglomerate phase of a bent-core material was studied for the first time, with rather low values, ~1x10-11 mV-2. The low Kerr constant can be understood in the context of the physical properties of the material. Supercooling phenomena in the blue phase were studied through an analysis of the optical properties in thin cells. Features including the Bragg reflection peak jump and hysteresis are measured through the reflection spectra. A blue phase sample with a single orientation over an area of millimeters was prepared to help the spectra study of the blue phases. Although some previous reports indicated that there may be a new blue phase in the supercooled region, we find that there is no evidence shows that the supercooled blue phase has a different structure from the BPI.Chiral molecules have been included as dopants in achiral bent-core materials to produce a range of new chiral mixtures. Different host materials and chiral dopants have been used to produce several chiral nematic materials in which the chiral nematic phase, the underlying smectic phase and the blue phases are examined. The order parameter is determined as a function of temperature in the chiral nematic phase, and compared to that determined for several calamitic materials; no discernible difference is found. A study of the pitch divergence in the chiral nematic phase of the bent-core mixtures shows interesting properties at both low temperature (as the smectic phase is approached) and at high temperatures (at the transition to the blue phase). An unusual phase separation of the chiral dopant in the mixtures is reported, and details are deduced through a comparison between different mixtures. It is found that a dopant with similar clearing point to the bent-core material has less likelihood of phase separation. Although the blue phase temperature range is extended in these mixtures in comparison with typical values for calamitic materials, it does not extend beyond 2K in any of the materials. Both blue phase I and the fog phases are observed in these chiral bent core systems, but no BPII is observed in any of the materials studied. The small k33 (~ 2.8 pN at 10 K below clearing point) in the bent-core host material is suggested as one of the reasons that the blue phase range is not enhanced as much as may have been expected from reports by other authors.

For the past 50 years, the magnetic storage industry has been the ultimate provider, covering the ever-expanding needs of digital mass storage. Up to now, scaling to smaller dimensions has been the core approach for achieving higher areal densities in conventional media. However, recent studies have shown that further miniaturisation is physically bound by superparamagnetic effects. Bit patterned media (BPM) is one of the most promising solutions for extending the areal densities beyond 1Tbit/in². The ability to magnetically characterise novel BPM is a key requirement for its future commercialisation. The work presented in this thesis describes the investigation of the Magneto-Optic Kerr Effect (MOKE) and the Anomalous Hall Effect (AHE) techniques, used in the characterisation of BPM samples. These samples were produced as part of this work using a customised subtractive fabrication process. Continuous thin magnetic films with Ptseed(10nm)/[Co(0.4nm)/Pt(1nm)]x15 composition and perpendicular anisotropy, were deposited using electron-beam (e-beam) evaporation, and subsequently patterned into magnetic nano-islands through means of e-beam lithography and Ar⁺ ion milling. In terms of the MOKE technique, a fully customised polar MOKE system has been developed and successfully used to observe the hysteretic behaviour of magnetic nano-island arrays with varying dimensions. An expected reduction in the MOKE signal due to pattering has been observed, as well as an additional signal reduction due to the scattering effect arising from the non-vertical sidewalls of the dome-shaped islands. In the case of islands with improved shape profile, the magnetic reversal of BPM arrays with islands sizes down to 35nm has been successfully detected, demonstrating a sensitivity of approximately 6x10⁻¹³emu for the MOKE system. In terms of the AHE technique, Au Hall crosses were deposited on top of the BPM arrays that had been previously characterised by MOKE, allowing the direct comparison and cross-verification of the results obtained by the two techniques. A revised Hall cross design, where the Hall crosses were generated by direct patterning of the Pt seed layer, has provided a significant improvement in AHE signal. This has allowed the detection of the magnetic reversal of individual sub-50nm magnetic islands, demonstrating a sensitivity of approximately 6.6x10⁻¹⁵emu for the AHE technique. The spatial sensitivity of these Hall cross structures has been experimentally determined, indicating a decrease in sensitivity with increasing distance from the cross centre and with decreasing island diameter. In conclusion, the sensitivity profile of Hall cross structures must be taken into account for the accurate interpretation of BPM characterisation results obtained by the AHE technique. Finally, some suggestions are outlined with regard to the future improvement of the developed characterisation techniques and the further continuation of the work presented in this thesis.

Domain wall dynamics is the one of the most interesting topics in the field of Spintronics because of its potential applications in the development of memory devices. These studies of dynamics are particularly focused on dilute magnetic semiconductors (DMS) or ferromagnetic semiconductors, which are believed to be one of the future materials for Spintronics devices. Despite the fact that the Curie temperature of these DMS is still lower than room temperature the knowledge gained in this study can be applicable to other DMS systems and will unravel new phenomena for the dynamic behavior of domain walls. In this work the dynamic behavior of magnetic domain walls in (Ga, Mn) (As, P) nanometric layers was studied. This was achieved with the use of longitudinal Kerr microscopy working at cryogenic temperature. The domain wall displacements were measured with the application of high enough magnetic fields for very short durations at two different temperatures. These magnetic fields were applied with the help of homemade microcoils used for the first time in this kind of study on DMS. A comparison is shown with the previous results obtained on the same material with a different magnetic anisotropy. The results show very high domain wall velocities for this type of material, not reported previously. The velocity curves clearly show two distinct regions with different mobilities. Finally quantitative analyses are presented to explain these velocities.

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