The magneto-optical Faraday effect has been used to observe the spin-bath relaxation at low temperatures in CeES and in Eu-doped CaF₂. The paramagnetic Faraday rotation ϩ is an instantaneous measure of the magnetization M and it is shown that in CeES and Eu²+ : CaF₂, ϩ∾ M at the light frequencies employed. The apparatus is the same as that previously described by Rieckoff and by Griffiths. Pulsed MW-power at X-band has been used to disturb the equilibrium between spin system and bath. In CeES, the observed relaxation time Շ is of the order of a few msec, which is several orders of magnitude longer than the theoretical estimate of T₁. This suggests a severe bottleneck in the energy transfer spin-bath. Շis found to be environment-dependent. In HeII, the relaxation is exponential. Շ is in good agreement with nonresonant relaxation measurements by Van den Broek and Van der Marel. It is explained as arising from the Kapitza boundary resistance at the CeES-HeII interface. In HeI, the relaxation is non-exponential and is slower than in He gas at the same temperature. This suggests that in this case the thermal diffusion in the helium around the crystal is the bottleneck. The same relaxation behaviour is found when the crystal is heated dielectrically with MW power far off resonance. This supports the assumption that the energy transfer spin-bath is limited by spatial diffusion. If the crystal is surrounded by a He film at a temperature below the λ-point, Շ is found to be the same as in HeII up to a well defined average MW power level. For higher powers the relaxation behaviour is similar to that of CeES immersed in HeI. In Eu²+ ; CaF₂, T₁ is expected to have the form T₁= AT + BT⁵. The observed relaxation time Շ , however, is found to be concentration dependent. All measurements have been done on the +½⇢ -½ transition with H II [100]. For the three lowest concentrations, the temperature dependence of Շ from 1.5 to 4.2°K can be fitted with the expression Շ ¯¹=CT with C = 2.75 (sec°K) ¯¹ for 0.02% Eu, C = 3.5for 0.8% and C = 5 for 0.2%, Շ is shorter and Շ ¯¹ ∾ T ² from 1.5°K to 7°K. The concentrations given correspond to the total Eu content. The Eu²+ concentration has been inferred from the magnitude of the saturation rotation. Շ(T) seems to depend on both Eu²+ and Eu³+ concentrations. It is suggested that exchange coupled pairs of Eu²+ and clusters involving Eu³+ may account for the concentration dependence of Շ. Upper limits of A = 2.5 and B = 5 x 10¯⁵ are found for T₁ by extrapolating the lowest concentrations investigated. These values are somewhat lower than both measured and calculated values found by Huang. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The study of pulsed n. m. r. in single crystal metallic samples, initiated by McLachlan, has been extended to liquid helium temperatures with special emphasis on Sn¹¹⁹ . Contrary to McLachlan's belief it was found that cooling to 4. 2°K and lower afforded significant improvements to the signal to noise ratio and in many cases the n. m. r. signals (including spin echoes in Sn¹¹⁹ ) could readily be seen on an oscilloscope without the use of a signal averager. The theory of magnetic resonance in metallic samples was studied in some detail with particular emphasis on the experimental situation where matters are complicated by the high conductivity which modulates both the amplitude and the phase of the exciting r.f. magnetic field as it penetrates into the sample. It is shown theoretically that several assumptions must be made to show that the conventional methods of pulsed n. m. r. used to measure T₂ (by either spin echo or free induction decay) and T₁ yield true meaningful results. In particular it is found that the spin lattice relaxation time T₁ is obtained by the conventional two pulse sequence only when the magnetic field is exactly on resonance; this was observed to be the case experimentally as well. In sharp distinction to McLachlan's findings for Sn¹¹⁹, the spin-spin relaxation time T₂ obtained by FID methods (175 ± 18μsec) was much smaller than that obtained by spin echo techniques (390 ± 48μsec) in the present research on Sn¹¹⁹. The spin-lattice relaxation time was also measured at liquid helium temperatures and yielded a value of 56 ± 4 millisec deg for T₁, in excellent agreement with Dickson although twice as large as McLachlan’s value. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Electron paramagnetic resonance (EPR) signals from tuna ferricytochrome c solutions were obtained between 4.2°K and 77°K, with g-values g(1) = 1.25, g(2) = 2.25, g(3) = 3.05« The g(3) line is 380 gauss wide between 4.2°K and 50°K with Gaussian shape, but has become 700 gauss wide with Lorentzian shape at 77°K. The temperature independent shape and width are best explained by a distribution of rhombic crystal field potentials (r.m.s. deviation = 11%). The Lorentzian shape arises from a short (10(-8) sec.) spin-lattice relaxation time. EPR spectra from horse heart ferricytochrome c single crystals were analysed to obtain the orientation of the g-axes relative to the crystallographic axes. The g(3)-axis was 76° from the crystal c-axis, close to the heme normal (71.5° to c-axis) determined from the 3-dimensional X-ray structure by Dickerson. The other 2 g-axes lay approximately along the N-Fe-N directions in the heme ring. An amended version of Eisenberger and Pershan's theory was used to explain the angular variation of the broad lines (300-2000 gauss) seen in the crystals—best fit was obtained with the distribution of ligand fields from the solution study plus a 1.5° variation in g-axis orientation. The undifferentiated absorption line shapes observed at 4.2°K in both solutions and single crystals were explained by the Portis theory of rapid adiabatic passage in solids. This theory was tested with a model system of charred dextrose, and found to be valid. Using the theory the relaxation time (τ) of the cytochrome c system was found to be, from the phase lag of the EPR signal relative to the magnetic field modulation, 3.8 x 10(-6) sec. at 4.2°K. τ was obtained between 4.2°K and 18°K from the rapid passage signals, and between 50°K and 70°K from the linewidth of the spectra. The temperature dependence of τ below 20°K could arise from a combination of a T(9) Raman spin-lattice relaxation process with a temperature independent spin-spin relaxation time of order 10(-8) seconds (which might arise from dipolar interactions between neighboring iron atoms). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Previous measurements on CdS (I) have shown a temperature shift in the single electron spin resonance (ESR) impurity band line. At 34 GHz this shift was found to be: dg= - 2.5 x 10ˉ ⁴/°K dT in going from 4.2°K to 1.7°K. This thesis presents the construction and testing of a metal temperature controlled dewar for the purpose of measuring the shift over the temperature range from 40°K to 1.7°K using an X-band (9 GHz)spectrometer. The signal was observed between 1.7°K and 4.2°K but rapidly broadened and could not be seen at higher temperatures. Since the lowest attainable temperature of the metal dewar was around 5°K, it could not be used as planned. Further studies using glass dewars proved that the g-shift at 9 GHz was too small, to be measured. The theory for the g-shift is discussed and the performance of the dewar evaluated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A cryostat has been built for cooling specimens to temperatures of the order of a hundredth of a Kelvin by thermal contact with an adiabatically demagnetized paramagnetic salt pill. The apparatus was designed for performing nuclear orientation experiments. This thesis describes the construction of the apparatus and experimental tests studying the nuclear orientation of (60)Co in an iron plate. The paramagnetic salt used was chromium potassium alum in an alum-glycerine slurry. In addition to the chrome alum pill a guard pill of manganous ammonium sulphate was used between the alum pill and the 1K helium bath. The pills were supported and thermally isolated by German silver spacers. A copper heat link was embedded in the alum-glycerine slurry and soldered to the specimen to provide thermal contact. Several heat links were used ranging from a bundle of five thousand copper wires to a copper foil "concertina" arrangement. A Ventron niobium-titanium superconducting solenoid which produced fields up to 48 kilogauss was used for the magnetic cooling. A superconducting polarizing solenoid was used to magnetically saturate the polycrystalline iron plate. Anisotropies in the gamma radiation intensity from (60)Co of 7 to 11 per cent corresponding to temperatures of 37 to 45 m K were observed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The electronic g-tensor in antimony doped cadmium sulphide has been measured at 1.1°K. A sample doped to a room temperature resistivity of 3.3 ohm-cm exhibited an anisotropic g-tensor with g// = 1.788 and g⊥ = 1.770. A single asymmetric line was observed. The asymmetry of this line was found to decrease with decreasing incident power. Further experiments to study this line shape are indicated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The ESR g-value and susceptibility measurements for DMTM(TCNQ)₂ have been studied as a function of angle made by crystal with magnetic field and temperature. The angular dependence of g-value is fitted to g² = α+βcos2θ - γsin2θ for three orthogonal directions of crystal rotation. The principal g-values are close to those expected for TCNQ compounds: g₁ = 2.0034, g₂ = 2.0030, g₃ = 2.0024. The susceptibility as a function of temperature agrees with bulk susceptibility measurements except that the maximum position occurs at about 30 K. The results of Oostra et al. for bulk susceptibility showed a maximum at around 50 K. The phase transition reported by Visser et al. at 272 K is observed in the ESR data as a 15% decrease in susceptibility. The linewidth is remarkably anisotropic typical of TCNQ salts. The phase transition study is done for two orientations of the crystal with the magnet field. In one of the orientations the linewidth narrows from 0.15 to 0.11 gauss and in the other it narrows from 0.24 to 0.18 gauss. In the former case there is a growth of a second line due to the twinned stack; transformation twinning takes place at the phase transition. A small level-crossing interaction is inferred from the change in relative intensities of the lines near the crossover. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A gas of atomic hydrogen confined at and below 1K in a sealed cell has been studied by magnetic resonance at the zero-field hyperfine transition frequency of 1420 MHz. A review is presented of magnetic resonance theory for a two level system, with emphasis on determination of the absolute magnetization by two methods: calibration of the spectrometer sensitivity and by use of the radiation damping time constant. Measurements at 1K on a gas at low density, 10¹¹<n[sub=H]<5x10¹² cm⁻³, in the saturated ⁴He vapour density have yielded the rate for the reaction H+H+He￫H₂+He, the diffusion constant and pressure shift of the hyperfine transition for H interacting with the He gas, and the cross-section for spin exchange relaxation. At temperatures below 1K, measurements of the frequency shift and effective recombination rate for H adsorbed on the He film have yielded values of the binding energies for H on ³He and for H on ³He as well as the hyperfine transition frequency shift and surface recombination rate for H adsorbed on each of these surfaces. The binding energies are found to be 1.15(5) K for H on ³He and 0.42(5) K for H on ³He. Measurements have been carried out at temperatures as low as 162 mK for H on ³He and 65 mK for H on ³He. lineshape for H atoms undergoing occasional sticking events on the helium surface. This model has been applied to frequency shift and transverse relaxation data at low temperatures to yield sticking probabilities of 0.046(5) for H on ³He and 0.016(5) for H on ³He. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis presents the results of the first application of a novel solid state nuclear magnetic resonance technique (K. P. Pauls et. al., Eur. Biophys. J. 11:1) to a naturally occuring membrane polypeptide. Deuterium NMR was used to study the structure and dynamics of hydrogen-exchanged gramicidin A', an ion channel, in model membranes. The technique exploits recently developed procedures for solvent-signal suppression (P. T. Callaghan et. al., J. Magn. Reson. 56:101), and "depakeing" powder spectra (E. Sternin, M.Sc. Thesis,U.B.C.). The spectra of gramicidin A' in crystalline form, and in the gel phase of the lipid bilayer are similar and indicate little molecular motion on the NMR timescale. In the liquid crystalline phase, however, the spectra suggest rapid uniaxial rotation of the gramicidin about the bilayer director. The frequencies of the liquid crystalline phase spectra were found to be independent of bilayer thickness, temperature, and the presence of sodium chloride, in the ranges investigated. The results are discussed in the context of the conduction properties of the gramicidin ion channel, other spectroscopic studies, and thecretical models of the structure and action of gramicidin. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The studies presented in this thesis are in two areas. An investigation of aromatic nitrene molecules using EPR spectroscopy was undertaken. This revealed a general tendency for these molecules to exhibit two forms when trapped in a crystalline lattice. This is qualitatively interpreted as a perturbing effect of nitrogen evolved during generation from the azide. Single crystal experiments were made on 2,4,6-tribromophenyl nitrene, which exhibited an unusually large anisotropy in the zero field splitting, implying a bent structure. Temperature variation of several aromatic nitrene zero field splittings were made. The variation was interpreted as thermal averaging amongst states possessing different zero field parameters. The nature of these states however, could not be inferred. The variation is compared with similar studies. A computer program to least squares fit EPR angular data to a spin Hamiltonian has been written. This programme was used to obtain a description of the angularly dependent EPR data from an aromatic nitrene, and also for a radical species with a large hyperfine interaction. / Science, Faculty of / Chemistry, Department of / Graduate