The archetypal high temperature superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] has been extensively investigated. However, until now, little has been known about the behaviour of the magnetic vortices inside the Vortex Glass and liquid state. µSR measurements have shown a negative skewness for the field probability distributions in these regimes. Such a negative skewness has only recently been explained as being a direct consequence of three-body correlations between vortices in a similar layered superconductor. With a new understanding and knowledge of the physics of these systems, it is instructive to re-visit the superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] to explain the evolution of these three-body correlations occurring here. Comparing this with the ion-irradiated superconductors (of the same Bi₂Sr₂CaCu₂O[subscript[8+δ]] material), allows one to observe how three-body correlations between vortices evolve differently to that in the pristine material. Moreover, in the region of the macroscopic irreversibility line, entropically driven disorder exists below the matching field B[subscript[ϕ]] , whilst there is the appearance of relatively straight vortex lines at fields above B[subscript[ϕ]] . Such phenomena suggest a significant di fference in the evolution of three-body correlations compared with the unirradiated material. There has been much work conducted on the interplay between superconductivity and magnetism in materials of reduced dimensions. Work presented here on the ferromagnet/superconductor trilayer system (Permalloy/Nb/Permalloy) has shown a novel magnetic profile at the interface between the ferromagnetic and superconducting boundary, where, contrary to what is expected, the magnetism appears to be significantly suppressed at the interface before increasing towards the centre of the Nb layer.

Chan Fu-wai = 非晶態鐵磁性鐵-磷-碳合金的製作 / 陳輔偉. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Chan Fu-wai = Fei jing tai tie ci xing tie-lin-tan he jin de zhi zuo / Chen Fuwei. / Acknowledgments --- p.i / Abstract --- p.ii / Table of Content --- p.iv / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Nucleation --- p.1 / Chapter 1.1.1 --- Homogenous nucleation --- p.1 / Chapter 1.1.2 --- Heterogeneous nucleation --- p.4 / Chapter 1.2 --- The crystal growth --- p.5 / Chapter 1.2.1 --- The solid-liquid interface --- p.5 / Chapter 1.2.2 --- Lateral growth --- p.6 / Chapter 1.2.3 --- Continuous growth --- p.6 / Chapter 1.3 --- Non-equilibrium process --- p.8 / Chapter 1.3.1 --- Reduction of impurities --- p.8 / Chapter 1.3.2 --- Suppression of crystal growth --- p.8 / Chapter 1.4 --- The change in metallurgy --- p.9 / Chapter 1.4.1 --- The metallic glass --- p.9 / Chapter 1.4.2 --- The properties of glass --- p.10 / Chapter 1.4.3 --- The development of amorphous alloy --- p.11 / Chapter 1.5 --- Preparation methods of amorphous alloy --- p.12 / Chapter 1.6 --- The criterion of glass formation --- p.14 / Chapter 1.7 --- The study of this project --- p.15 / Reference --- p.16 / Figure --- p.19 / Chapter Chapter 2: --- Experiment --- p.36 / Chapter 2.1 --- Preparation --- p.36 / Chapter 2.2 --- Experimental procedure --- p.37 / Chapter 2.3 --- Sample analysis --- p.38 / Reference --- p.41 / Figure --- p.42 / Chapter Chapter 3: --- The formation of bulk ferromagnetic Fe-P-C amorphous alloy --- p.45 / Abstract --- p.45 / Introduction --- p.46 / Experiment --- p.47 / Result --- p.48 / Reference --- p.49 / Figure --- p.52 / Chapter Chapter 4: --- Compaction of bulk ferromagnetic Fe-P-C amorphous alloy --- p.57 / Abstract --- p.57 / Introduction --- p.58 / Experiment --- p.58 / Result --- p.60 / Reference --- p.61 / Figure --- p.62 / Chapter Chapter 5: --- Conclusion --- p.65

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I have measured the magnetic and transport properties of Fe and Co in the variable SDW host, CrMo. Analyzing the behaviour of the Neel temperature shows that Co interacts with the SDW, almost an order of magnitude more strongly than does Fe. Also that it magnetically polarizes the SDW more strongly than Fe. Resistivity measurements show that Co reduces the nesting area of the Fermi surface while Fe increases it. Overall, the Neel temperature is strongly reduced by Fe and much less reduced by Co. / Magnetic susceptibility measurements show that Fe supports an effective magnetic moment below T(,N) while Co does not. However, as suggested by Friedel, only nearest neighbour Fe pairs contribute to the effective Fe moment, while isolated Fe moments, like Co, are locked into the SDW antiferromagnetism. / In the absence of SDW formation, the strong interaction between Co and the CrMo host leads to a Kondo state, while the smaller interaction with Fe allows the onset of spin glass ordering.

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Magnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles are found to behave ferromagnetically for diameters below a few nanometers. Some of these manifestations are still intriguing, and novel research approaches are necessary to advance towards a more complete understanding of these exciting nanoscale systems. In particular, the ability to study an isolated individual nanoscale system (i.e just one molecule or nanoparticle) is both challenging technologically and fundamentally essential. It is expected that accessing to the energy landscape of an isolated molecule/nanoparticle will allow unprecedented knowledge of the basic properties that are usually masked by collective phenomena when the systems are found in large ensembles or in their crystal form. Several approaches to this problem are currently under development by a number of research groups. For instance, some groups are developing deposition techniques to create patterned thin films of isolated magnetic nanoparticles and molecular magnets by means of optical lithography, low-energy laser ablation, or pulsed-laser evaporation or specific chemical functionalization of metallic surfaces with special molecular ligands. However, it is still a challenge to access the properties of an individual molecule or nanoparticle within a film or substrate. iv I have studied molecular nanomagnets and ferromagnetic noble metal nanoparticles by means of a novel experimental approach that mixes the chemical functionalization of nano-systems with the use of single-electron transistors (SETs). I have observed the Coulomb-blockade single-electron transport response through magnetic gold nanoparticles and single-molecule magnet. In particular, Coulomb-blockade response of a Mn4-based SET device recorded at 240 mK revealed the appearance of two diamonds (two charge states) with a clear switch between one and the other is indicative of a conformational switching of the molecule between two different states. The excitations inside the diamonds move with magnetic field. The curvature of the excitations and the fact of having them not going down to zero energy for zero magnetic field, indicated the presence of magnetic anisotropy (zero-field splitting) in the molecule. In addition, the high magnetic field slope of the excitations indicates that transitions between charge states differ by a net spin value equal to 9 (|∆S| = 9), as expected from the behavior of Mn4 molecules in their crystalline form. Anticrossings between different excitations are indicative of quantum superpositions of the molecular states, which are observed for the first time in transport measurements through and individual SMM.