Magnetic interlayer coupling is one of the central phenomena in spintronics. It has been predicted that the sign of interlayer coupling can be manipulated by electric fields, instead of electric currents, thereby offering a promising low energy magnetization switching mechanism. Here we present the experimental demonstration of voltage-controlled interlayer coupling in a new perpendicular magnetic tunnel junction system with a GdOx tunnel barrier, where a large perpendicular magnetic anisotropy and a sizable tunnelling magnetoresistance have been achieved at room temperature. Owing to the interfacial nature of the magnetism, the ability to move oxygen vacancies within the barrier, and a large proximity-induced magnetization of GdOx, both the magnitude and the sign of the interlayer coupling in these junctions can be directly controlled by voltage. These results pave a new path towards achieving energy-efficient magnetization switching by controlling interlayer coupling.

by Lee Koon Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Lee Koon Ho. / Acknowledgements --- p.i / Abstract --- p.ii / 論文摘要 --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.ix / Chapter Chapter I --- Introduction / Chapter 1.1 --- Review of magnetoresistance --- p.1 -1 / Chapter 1.1.1 --- Colossal magnetoresistance in rare earth manganites --- p.1 -2 / Chapter 1.1.2 --- Review of manganite multilayer system --- p.1-10 / Chapter 1.2 --- Research motivation --- p.1-12 / Chapter 1.2.1 --- Scope of the thesis --- p.1-14 / Reference --- p.1-15 / Chapter Chapter II --- Instrumentation --- p.2-1 / Chapter 2.1 --- Facing target sputtering system --- p.2-1 / Chapter 2.1.1 --- Preparation of LCMO/PCMO multilayer thin film --- p.2-3 / Chapter 2.2 --- Annealing system --- p.2-5 / Chapter 2.2.1 --- Oxygen post-annealing system --- p.2-5 / Chapter 2.2.2 --- Vacuum annealing system --- p.2-7 / Chapter 2.3 --- X-ray diffraction (XRD) --- p.2-9 / Reference --- p.2-11 / Chapter Chapter III --- Annealing of LCMO/PCMO multilayer thin films --- p.3-1 / Chapter 3.1 --- Oxygen post-annealing of LCMO/PCMO multilayer thin film --- p.3-1 / Chapter 3.1.1 --- Introduction to post-annealing of managanites oxides --- p.3-1 / Chapter 3.1.2 --- LCMO and PCMO Single Layer Films Description --- p.3-1 / Chapter 3.1.3 --- Selection of PCMO --- p.3-5 / Chapter 3.1.4 --- La2/3Ca1/3MnO3/ Pr2/3Ca1/3MnO3 Multilayer Description --- p.3-5 / Chapter 3.1.5 --- Oxygen post-annealing condition --- p.3-9 / Chapter 3.1.6 --- Oxygen post annealing of P100 --- p.3-9 / Chapter 3.1.7 --- Conclusion --- p.3-16 / Chapter 3.2 --- Vacuum annealing of LCMO/PCMO multilayer thin films --- p.3-19 / Chapter 3.2.1 --- Introduction --- p.3-19 / Chapter 3.2.2 --- Sample description --- p.3-20 / Chapter 3.2.3 --- Vacuum annealing condition --- p.3-21 / Chapter 3.2.4 --- Vacuum Annealing of LCMO and PCMO --- p.3-23 / Chapter 3.2.5 --- Vacuum Annealing of LCMO/PCMO multilayer thin films --- p.3-29 / Chapter 3.2.6 --- Conclusion --- p.3-49 / References --- p.3-50 / Chapter Chapter IV --- Activation energy of small polaron in LCMO/PCMO multilayer thin films --- p.4-1 / Chapter 4.1 --- Introduction to small lattice polarons --- p.4-1 / Chapter 4.2 --- Theory of small polarons --- p.4-2 / Chapter 4.3 --- Activation energy of small polaron --- p.4-3 / Chapter 4.4 --- Discussion --- p.4-7 / References --- p.4-8 / Chapter Chapter V --- Conclusions --- p.5-1

No description available.

Research into molecular magnetism has undergone a revival over the past two decades following the discovery of Single Molecule Magnetism (SMM). Compounds which show this property have the potential to increase the storage capacity of magnetic media by many orders of magnitude compared to current generation devices. Developments in the field have come from synthesis involving mainly simple bridging ligands such as carboxylates, alkoxides, pyridonates and heterocyclic ligands. The use of phosphonic acid ligands in the synthesis of 4f-phosphonate or 3d-4f phosphonate clusters has recently begun to be explored, primarily for interest into their magnetic properties. The present work builds on studies which show that the reaction of oxo-centred metal triangles with phosphonate ligands can generate larger clusters retaining some motifs of the starting material. There are only few examples on the use of lanthanide carboxylates, such as [Ln2(O2CtBu)6(HO2CtBu)6] (Ln = Dy, Gd, Tb, Ho or Er) and/or a preformed cluster [Cr(III)3(µ3-O)(O2CtBu)6(H2O)3][O2CtBu] in combination with phosphonate ligands. This work investigates the use of bi-metallic lanthanide and tri-metallic transition metal starting materials in conjunction with the flexible tertiary-butylphosphonic acid ligand, to yield novel 4f-phosphonate and 3d-4f cages. Several Cr-4f phosphonate cages have been obtained, where each structure contains two oxo-centred {Cr3} triangles, bridged by phosphonates and lanthanides. Additionally, new 4f-phosphonate clusters have been synthesised by treating tertiary-butylphosphonic acid ligand with lanthanide nitrate salts or preformed lanthanide dimers. A number of 4f-phosphonate cages reported in the thesis show interesting structural or magnetic properties, for example, {Ln10P6} is the largest 4f-phosphonate odd number metal ring centred by a tenth metal site, the {Gd8P6} cluster demonstrates interesting MCE properties, and the {Dy4P2} complex is shown to be an SMM.

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

Ren, Zhiyuan. / "March 2001." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (p. 137-143). / 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.

by Li Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Li Ho. / Abstract --- p.i / 論文摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.viii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Magnetoresistance --- p.1 / Chapter 1.1.1 --- Giant magnetoresistance (GMR) --- p.3 / Chapter 1.1.2 --- Colossal magnetoresistance (CMR) in perovskite manganites --- p.5 / Chapter 1.1.2.1 --- Perovskite-type structure --- p.5 / Chapter 1.1.2.2 --- Metal-insulator transition --- p.7 / Chapter 1.1.2.3 --- Possible origin of CMR --- p.11 / Chapter 1.2 --- Low field magnetoresistance in CMR materials --- p.12 / Chapter 1.2.1 --- Single crystal and polycrystalline perovskite manganites --- p.12 / Chapter 1.2.2 --- Manganite trilayer junctions --- p.13 / Chapter 1.2.3 --- Possible mechanism of low field MR --- p.15 / Chapter 1.3 --- Our motivation --- p.15 / Chapter 1.3.1 --- Brief review of several manganite multilayer systems --- p.16 / Chapter 1.3.2 --- Scope of this thesis work --- p.18 / Reference --- p.19 / Chapter Chapter 2 --- Preparation and characterization of manganite thin films / Chapter 2.1 --- Thin film deposition --- p.22 / Chapter 2.1.1 --- Facing-target sputtering (FTS) --- p.22 / Chapter 2.1.2 --- Vacuum system --- p.25 / Chapter 2.2 --- Fabrication and characterization of PCMO and LCMO targets --- p.27 / Chapter 2.3 --- Epitaxial growth of LCMO thin films --- p.31 / Chapter 2.3.1 --- Substrate materials --- p.31 / Chapter 2.3.2 --- Deposition conditions --- p.32 / Chapter 2.3.3 --- Deposition procedure --- p.33 / Chapter 2.3.4 --- Results and discussions --- p.34 / Chapter 2.3.4.1 --- Morphology --- p.35 / Chapter 2.3.4.2 --- Structure --- p.39 / Chapter 2.3.4.3 --- Transport properties --- p.42 / Chapter 2.3.4.4 --- Conclusion --- p.48 / Chapter 2.4 --- Epitaxial growth of PCMO thin films --- p.49 / References --- p.51 / Chapter Chapter 3 --- LCMO/PCMO multilayer / Chapter 3.1 --- Sample preparation --- p.53 / Chapter 3.2 --- Results and discussion --- p.53 / Chapter 3.2.1 --- Structure characterization --- p.55 / Chapter 3.2.2 --- Transport properties --- p.59 / Chapter 3.2.3 --- Low-field magnetoresistance --- p.55 / Chapter 3.2.4 --- Magnetization --- p.73 / Chapter 3.3 --- Conclusion --- p.76 / References --- p.77 / Chapter Chapter 4 --- Conclusions --- p.78

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.

Abstract not available

Graduation date: 2000