Measurements of the evolution of the magnetic moment of nonideal (i.e. pinning rich) type II superconductors in stationary magnetic fields H a as a function of time at constant temperatures T < Tc or as the temperature is varied to or from Tc provide insight into the dynamics of flux lines and their interactions with the pinning sites. Three concentric magnetic moments coexist in these materials when the isothermal sweep of Ha causes the locus of the magnetization ⟨M⟩ to migrate along any path joining the upper with the lower envelopes of the major hysteresis curves. The "outermost" magnetic moment is always diamagnetic and is generated by the field opposing Meissner surface current. The two other magnetic moments fill the bulk of the specimen, currents circulating in one direction in the outer annular volume embrace an inner volume occupied by counter-rotating persistent currents. In semi-reversible type II superconductors the magnitude of the Meissner magnetic moment is important compared to that arising from the currents in the bulk whereas in very hysteretic specimens it is negligible. In both types of material it is a fairly straightforward procedure to establish configurations in various static Ha where the opposing magnetic moments exactly cancel each other so that the macroscopic net magnetization is zero. However the internal pattern of persistent currents and magnetic flux density profiles which prevail in these special ⟨M⟩ = 0 states is complicated, fascinating and provides a full crucible for the investigation of flux line behaviour. In this thesis I present the results of our experimental study of the evolution of the magnetization of these initial ⟨M⟩ = 0 states during warming to Tc as a function of the static applied field H a. The phenomena encountered are seen to depend dramatically on the direction of the change of Ha causing ⟨M⟩ to migrate from one envelope of the major hysteresis loop to the opposite. Further we find major differences in the behaviour exhibited by the semi-reversible type II superconductors in comparison with that manifested by the highly hysteretic samples. We also see that the low Tc and high Tc semi-reversible specimens display very similar but highly intricate behaviour. Finally we show that a simple model which exploits the critical state concept and applies the principle of conservation of flux lines can account for the major features of all our observations.

Magnetic susceptibility studies over the temperature range 87-330°K, on sixteen complexes of copper (11) are reported. The compounds are conveniently divided into two groups. Group I compounds (copper (11) benzoate and its monopyridine adduct, copper (11) meta-chlorobenzoate and its monopyridine and mono-p-dioxane adducts and the monopyridine and hemipyridine adducts of copper (11) para-chlorobenzoate ) possess magnetic properties expected for a binuclear system and values of the exchange integrals have been calculated, for these compounds. The group 11 compounds (the dipyrldlne adducts and the basic salts of copper (ll) benzoate, copper (11) ortho-, meta- and para-chlorobenzoate ) exhibit only weak magnetic interaction --- their magnetic susceptibilities obeying the Curie-Weiss law with small Weiss constants --- and they are considered to have polymeric structures. Copper (11) para-chlorobenzoate exhibits properties intermediate between the group I and 11 compounds. Confirmatory evidence for assigning binuclear structures to the group I compounds has been obtained from the presence, in the spectra of the group I compounds, of a band at about 400 mμ which is absent from the spectra of the group 11 compounds. Infrared spectra are reported for all the compounds studied and a partial assignment has been made. / Science, Faculty of / Chemistry, Department of / Graduate

The nuclear magnetic resonance technique has been used to study the effect of deuteration on the Neel temperature of CoCl₂•6H₂0 single crystals. The Neel temperature varies with a period of 180° as the external magnetic field is rotated about the b-axis⊥ the a-c plane. On deuteration, the Neel temperature rises for all orientations, the more deuterium being introduced the higher the transition point. The maximum increase of approximately 6% in Neel temperature is obtained with a 92% concentration of deuterium. In addition, the anisotropy in TN decreases from approximately 0.08°K for 0% deuteration to slightly less than 0.05°K for 92% deuteration. Further, the orientation-averaged Neel temperature seems to vary linearly with the cube root of relative concentration of deuterium. In the vicinity of H₀ = 4,000 gauss, the Neel temperature increases with an increase in the external magnetic field [formula omitted] being ⊥ c-axis. This unusual behaviour is common to deuterated as well as non-deuterated samples and has not yet been explained. Following Haseda's conjecture, a semi-empirical attempt is made to establish a connection among the change in Neel temperature upon deuteration, the super-exchange parameter and the potential of a proton in a hydrogen bond. The picture presented is that the Neel temperature rises on deuteration because of a change in the average of the super-exchange parameter over the ground vibrational state of the hydrogen atom. An x-ray analysis shows that at room temperature the CoCl₂•6H₂0 and CoC1₂•6D₂0 crystals have the same symmetry and their cell dimensions do not differ by more than 0.2%. The infra-red spectrum of CoC1₂•6D₂0 has been used to determine the value of electrostatic field gradient at the deuteron sites. This value is consistent with the observed quadrupole splitting of the n.m.r. spectrum of the deuterons. The n.m.r. lines belonging to deuterons in the water molecules not forming a square configuration around cobalt ions have been identified. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Geomagnetic depth-sounding was carried out in a large-spaced profile across central British Columbia in order to map the conductivity structure of the crust and upper mantle in the central Canadian Cordillera. Geomagnetic variographs were set up from east of Jasper to Prince Rupert in two successive east-west profiles during the summer of 1969. Numerical analysis of geomagnetic storm activity indicates that the discontinuity in the attenuation of the vertical magnetic field, as first reported for south-eastern British Columbia by Hyndman (1963), is located in the area of the Rocky Mountain Trench. All stations to the west exhibit typical 'low Z' characteristics and no or little anomalous induction; stations to the east of the trench display a strong, high-frequency Z-variation content as well as anomalous field enhancement. Power spectral and polarization analyses show a first order agreement with the two-dimensional conductivity structure model proposed by Caner (1970) for south-western Canada. Second-order effects suggest a more complex model consisting of two conductivity discontinuities: One shallow structure strikes roughly NW-SE at a depth of 10 to 15 km. and may be associated with the 'edge' of a hydrated layer located at the western front of the Rocky Mountains; a second much deeper structure, trending approximately E-W, is located south of Kootenay Lake and is possibly associated with a strike-slip feature in the upper mantle (Lajoie and Caner, 1970). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Graphene – a monolayer of carbon atoms densely packed in a honeycomb lattice – was isolated for the first time in 2004 and, since then, has established itself as one of the most remarkable materials available to condensed matter scientists today. Theory predicts a whole spectrum of magnetic phenomena in graphene, including several mechanisms for intrinsic ferromagnetism and spin-ordering effects that arise due to its low-dimensionality and highly unusual electronic properties (e.g. Dirac-like spectrum). In this experimental work, SQUID (Superconducting Quantum Interference Device) magnetic measurements have been carried out in graphene laminates with masses up to ≈ mg obtained by ultrasonic exfoliation of highly oriented pyrolytic graphite (HOPG) in N-methyl-pyrrolidone (NMP). Scanning electron microscopy (SEM) and X-ray diffraction experiments revealed that the laminates are made of decoupled graphene crystallites with typical flake size below 50 nm. Atomic force microscopy (AFM) measurements carried out for graphene suspensions dispersed onto a SiO2 substrate allowed the recognition of thin crystallites associable to single and double-layer graphene. X-ray dispersive fluorescence (XRF) and electron dispersive diffraction (EDX) confirmed the laminates chemical purity with absence of metals and/or magnetic inclusions. Pristine laminates exhibit Curie paramagnetism noticeable below ≈ 50 K, which contributes to about one moment per crystallite at 2 K. The laminates are strongly diamagnetic, although a decrease of the diamagnetic susceptibility by about three times with respect to graphite was observed for fields applied perpendicularly to the ab plane. The same graphene laminates were employed as a reference system to study magnetism of point defects, such as fluorine adatoms and vacancies generated through ion irradiation. The unambiguous spin value J=1/2 found for both species of defects confirms theoretical expectations. In the case of fluorine atoms a magnetic moment of 1 µB per ≈ 1000 adatoms was obtained, associated to the tendency of fluorine to cluster in graphene. Vacancies produced a value of the magnetic moment much closer to the expected 1 µB for point defects. No sign of defect related ferromagnetism was observed. On the other hand, our study performed on NT-MTD HOPG crystals (the same adopted for the fabrication of our graphene laminates), revealed ferromagnetic signals up to 3∙10-3 emu/g. Backscattering electron microscopy (BSE), performed alongside EDX chemical analysis, confirmed that the observed magnetic behaviour is due to ferromagnetic inclusions, such as magnetite and titano-magnetite. Therefore, weak and poorly reproducible ferromagnetic-like signals in graphene laminates were attributed to the same contaminations present in the original material (i.e. HOPG).

A sensitive nuclear magnetic resonance spectrometer has been constructed using Field Effect Transistors in a Robinson configuration. The spectrometer has been used to study the anomalous nuclear magnetic resonance spectra of single crystals of NbSe₂. An analysis of the field dependence of the line width in the low temperature phase has demonstrated that this results from a distribution of Knight Shifts. Such a distribution is not consistent with a structural transformation involving only two nonequivalent sites as proposed by Ehrenfreund et al. In addition accurate measurements of the Knight Shift and electric field gradient tensor have been made in the high temperature phase at 77K and 300K. The Knight Shift has a very large anisotropic component but an almost zero isotropic component which is indicative of negligible s-electron character at the: Fermi surface. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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