The code is developed for the calculation of the magneto-crystalline anisotropy (MAE) in thin films using a classical Heisenberg hamiltonian with a correction developed by Van Vleck. A Metropolis style Monte Carlo algorithm was used with adequate corrections to accelerate the calculation. The MAE was calculated for the case of a thin film with an increasing number of defects on the top layer for the cases where the defects were distributed randomly and when they assumed ordered positions. The results obtained agree qualitatively with the results provided by the literature and with the theory. / Graduation date: 2003

The magnetic recording media used for hard disks in laptops and PC's is constantly being improved, leading to rapid increases in data rate and storage density. However, by the year 2010, it is predicted that the superparamagnetic limit will be reached, which is potentially insufficient for data storage. At the beginning of this century, CoCr -based alloys are used in longitudinal media since cobalt has a high magnetocrystalline anisotropy. In this thesis, the static and dynamic properties of longitudinal recording thin films were investigated in order to explain and correlate their magnetic characteristics to their recording properties. The samples in question were test samples and some were in commercial use. Magnetic techniques such as high field ferromagnetic resonance and torque magnetometry were used to determine accurately the crystalline anisotropy field. High field ferromagnetic resonance is an ideal tool to determine the crystalline anisotropy, magnetisation, Lande g-factor and the gyromagnetic damping factor. In contrast to previous work, there are no FMR simulations and so all the relevant parameters were determined directly from measurement. Ideally, there should be no exchange interactions between the neighbouring cobalt grains; however, interactions between the grains within the CoCr-alloy recording layer exist. Previous work on the measurements of interactions in recording media involves measuring the sample's magnetisation. In this thesis, an alternative novel method involves torque magnetometry. Another technique that was used in this thesis is small angle neutron scattering, which aims to determine the size of the magnetic grains and compare that with the physical size determined from TEM, by Seagate. There is an extended section on CoxAg1-x granular thin films, which involves determining the sample's g-factor, effective anisotropy, grain size, exchange constant and comparing the FMR lineshapes at 9.5 and 92GHz.

Lo Kwok Wing. / Thesis submitted in: November 2003. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 95-98). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.ii / Table of Contents --- p.iii / List of Figures --- p.iv / List of Tables --- p.v / Chapter iii. --- Table of Contents / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Magnetic CoPt and FePt Alloys --- p.1 / Chapter 1.1.2 --- Crystal Structures --- p.2 / Chapter 1.1.3 --- Magnetic Properties --- p.5 / Chapter 1.2 --- Magnetic Nanocomposite Films --- p.6 / Chapter 1.2.1 --- Ferromagnetic CoPt & FePt Alloy Nanoparticles --- p.7 / Chapter 1.3 --- Preparation Methods of CoPt & FePt Nanocomposite Films --- p.8 / Chapter 1.4 --- Aim and Motivation of this Research Project --- p.9 / Chapter Chapter 2 --- Sample Preparation and Characterization Techniques --- p.11 / Chapter 2.1 --- Sample Preparation --- p.11 / Chapter 2.1.1 --- Metal Vapor Vacuum Arc (MEVVA) Implantation System --- p.11 / Chapter 2.1.2 --- Preparation Procedures --- p.13 / Chapter 2.2 --- Characterization Techniques --- p.18 / Chapter 2.2.1 --- Rutherford Backscattering Spectroscopy (RBS) --- p.18 / Chapter 2.2.2 --- X-ray Diffractometry (XRD) --- p.20 / Chapter 2.2.3 --- Atomic Force Microscopy (AFM) --- p.23 / Chapter 2.2.4 --- Vibrating Sample Magnetometry (VSM) --- p.24 / Chapter Chapter 3 --- Characterization of Co and CoPt Implanted Samples --- p.28 / Chapter 3.1 --- Composition of Implanted Samples --- p.28 / Chapter 3.2 --- Phase Evolution and Crystal Structures --- p.34 / Chapter 3.2.1 --- Phase Evolution with Annealing Temperature --- p.35 / Chapter 3.2.2 --- Grain Size of Implanted Samples --- p.37 / Chapter 3.3 --- Magnetic Properties --- p.37 / Chapter 3.3.1 --- Dependence of Hc on Film Compositions --- p.39 / Chapter 3.3.2 --- Dependence of Hc on annealing Temperature --- p.42 / Chapter Chapter 4 --- Characterization of Fe and FePt Implanted Samples --- p.44 / Chapter 4.1 --- Overview --- p.44 / Chapter 4.2 --- Low Dose Implanted Samples --- p.44 / Chapter 4.2.1 --- RBS --- p.44 / Chapter 4.2.2 --- Phase Formation and Crystal Structures --- p.48 / Chapter 4.2.2-1 --- Phase Evolution with Annealing Temperature --- p.49 / Chapter 4.2.3 --- Grain Size of Implanted Samples --- p.51 / Chapter 4.2.4 --- AFM Results --- p.53 / Chapter 4.2.5 --- Magnetic Properties --- p.55 / Chapter 4.2.5-1 --- M-H Characteristics --- p.55 / Chapter 4.2.5-2 --- Coercivity Against Annealing Temperature --- p.55 / Chapter 4.3 --- High Dose Implanted Samples --- p.61 / Chapter 4.3.1 --- RBS --- p.62 / Chapter 4.3.2 --- Phase Formation and Crystal Structures --- p.66 / Chapter 4.3.2-1 --- Phase Evolution with Annealing Temperature --- p.67 / Chapter 4.3.2-2 --- Grain Size of Implanted Samples --- p.70 / Chapter 4.3.3 --- Magnetic Properties --- p.72 / Chapter 4.3.3-1 --- M-H Characteristics --- p.73 / Chapter 4.3.3-2 --- Coercivity Against Annealing Temperature --- p.74 / Chapter 4.3.3-3 --- Low Temperature Measurements --- p.79 / Chapter 4.3.3-4 --- Coercivity against annealing time --- p.79 / Chapter 4.3.4 --- Microstructure --- p.84 / Conclusion --- p.88 / Appendices --- p.90 / Bibliolography --- p.95 / Publications --- p.98

Spintronics reaches beyond typical charge-based information storage technologies by utilizing an addressable degree of freedom for electron manipulation, the electron spin polarization. With mounting experimental data and improved theoretical understanding of spin manipulation, spintronics has become a potential alternative to charge-based technologies. However, for a long time, spintronics was not thought to be feasible without the ability to electrostatically control spin conductance at room temperature. Only recently, graphene, a 2D honeycomb crystalline allotrope of carbon only one atom thick, was identified because of its predicted, long spin coherence length and experimentally realized electrostatic gate tunability. However, there exist several challenges with graphene spintronics implementation including weak spin-orbit coupling that provides excellent spin transfer yet prevents charge to spin current conversion, and a conductivity mismatch due to the large difference in carrier density between graphene and a ferromagnet (FM) that must be mitigated by use of a tunnel barrier contact. Additionally, the usage of graphene produced via CVD methods amenable to semiconductor industry in conjunction with graphene spin valve fabrication must be explored in order to promote implementation of graphene-based spintronics. Despite advances in the area of graphene-based spintronics, there is a lack of understanding regarding the coupling of industry-amenable techniques for both graphene synthesis and lateral spin valve fabrication. In order to make any impact on the application of graphene spintronics in industry, it is critical to demonstrate wafer-scale graphene spin devices enabled by wafer-scale graphene synthesis, which utilizes thin film, wafer-supported CVD growth methods. In this work, high-quality graphene was synthesized using a vertical cold-wall furnace and catalyst confinement on both SiO2/Si and C-plane sapphire wafers and the implementation of the as-grown graphene for fabrication of graphene-based non-local spin valves was examined. Optimized CVD graphene was demonstrated to have ID/G ≈ 0.04 and I2D/G ≈ 2.3 across a 2" diameter graphene film with excellent continuity and uniformity. Since high-quality, large-area, and continuous CVD graphene was grown, it enabled the fabrication of large device arrays with 40 individually addressable non-local spin valves exhibiting 83% yield. Using these arrays, the effects of channel width and length, ferromagnetic-tunnel barrier width, tunnel barrier thickness, and level of oxidation for Ti-based tunnel barrier contacts were elucidated. Non-local, in-plane magnetic sweeps resulted in high signal-to-noise ratios with measured ΔRNL across the as-fabricated arrays as high as 12 Ω with channel lengths up to 2 µm. In addition to in-plane magnetic field spin signal values, vertical magnetic field precession Hanle effect measurements were conducted. From this, spin transport properties were extracted including: spin polarization efficiency, coherence lifetime, and coherence distance. The evaluation of industry-amenable production methods of both high-quality graphene and lateral graphene non-local spin valves are the first steps toward promoting the feasibility of graphene as a lateral spin transport interconnect material in future spintronics applications. By addressing issues using a holistic approach, from graphene synthesis to spin transport implementation, it is possible to begin assessment of the challenges involved for graphene spintronics.

Graduation date: 1995

No description available.

by Chiah Man Fat. / "March 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Xia, Daxue. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

No description available.

Thesis (Ph.D.) OGI School of Science & Engineering at OHSU, June 2008. / Includes bibliographical references.