This thesis uses ferromagnetic resonance to explore the current-induced torques (CITs) in two different systems, namely YIG/heavy metal bilayers and bulk NiMnSb, at room temperature. We apply a microwave current to the sample while sweeping the external magnetic field, and measure the longitudinal DC voltage. From a symmetry analysis of the ferromagnetic resonance lineshape, the amplitudes and directions of the CITs parameterised by an effective magnetic field are accurately estimated. In Chapter 4, YIG samples of different thickness, capped by either Pt or Ta, are studied. The resonance is driven by both spin-transfer torque and Oersted field, and the DC voltage is attributed to both spin rectification and spin pumping. The CITs can be well analysed from the lineshape of the voltage and its dependence on YIG thickness, from which we deduce that the Oersted field dominates over the spin-transfer torque in driving magnetization dynamics. In Chapter 5, we characterise the CITs in bulk NiMnSb induced by the relativistic spin-orbit coupling effect. Both field-like and antidamping-like spin-orbit torques are observed and analysed in detail. At the end of this chapter, we study the spin-wave resonance driven by the CITs, from which the exchange stiffness of NiMnSb is determined. In Chapter 6, we extrapolate a new form of magnetoresistance in NiMnSb: unidirectional spin-orbit magnetoresistance (USOMR). USOMR scales linearly with the current and has opposite sign when the magnetization is reversed. Similar to the giant magnetoresistance in magnetic multilayers, USOMR can be used to distinguish between two opposite magnetization directions directly in the bulk of the ferromagnet.

Le domaine de recherche de la spintronique vise a concevoir des dispositifs électroniques misant sur le degré de libre de spin pour transporter de l'information. An d'intégrer ces courants de spin dans des dispositifs électroniques, il est particulièrement intéressant d'étudier l'inter-conversion d'un pur courant de spin en un courant de charge par l'effet Hall de spin, ainsi que le transfert de moment angulaire entre les électrons de conduction d'un métal normal (NM) et l'aimantation d'un ferromagnétique (FM) (couple de transfert de spin / pompage de spin). An de mieux comprendre ces différentes interaction, cette thèse se concentre sur l'étude du système hybride constitué de la juxtaposition d'un ferrimagnétique isolant, le grenat d'yttrium fer (YIG), et d'un métal normal _a fort couplage spin-orbite (Pt ou Ta), nécessaire pour bénéficier de la polarisation en spin de l'interface par un courant électrique dans le plan. Nous avons étudié le pompage de spin et la magnétorésistance produite par l'effet Hall de spin a l'interface entre des bicouches de YIG j Pt et YIG j Ta, et ceci sur des lms étendus de YIG de 200 nm d'épaisseur, produits par épitaxie en phase liquide. Nous observons que la tension électrique, produite par l'effet Hall de spin inverse, change de signe entre du Pt et du Ta confirmant ainsi l'inversion des signes de l'angle de Hall entre ces deux matériaux. En outre, en mesurant la variation de la tension de Hall inverse en fonction de l'épaisseur de la couche de Ta, nous avons réussi à borner la longueur de diffusion de spin dans le Ta. Tant le YIG j Pt et le YIG j Ta affiche une variation semblable de la magnétorésistance a effet Hall de spin en fonction de l'orientation du champ magnétique. Pour étudier l'inuence interfaciale du pompage de spin… / Spintronics aims at designing electronic devices which capitalize on the spin degree of freedom to transport information using spin currents. In order to incorporate spin currents intoelectronic devices, it is particularly interesting to study the interconversion from a spin current, the motion of spin angular momentum, to a charge current (Spin Hall Effect) as well as the transfer of spin angular momentum between the conduction electrons of a normal metal (NM) and the magnetization of a ferromagnet (FM) (Spin Transfer Torque/Spin Pumping). To investigate the interplay of those effects this thesis studies hybrid systems of the ferromagnetic insulator Yttrium Iron Garnet and normal metals with large spin-orbit coupling, a prerequisite for spin Hall e_ect. We study spin pumping and spin hall magnetoresistance in YIGjPt and YIGjTa bi-layers using extended _lms of 200 nm thick YIG, grown by liquid phase epitaxy. The inverse spin Hall voltages in Pt and Ta confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we constrain the spin di_usion length in Ta. Both the YIGjPt and YIGjTa systems display a similar variation of resistance upon magnetic eld orientation, the spin Hall magnetoresistance. To study the inuence of interfacial spin pumping and a possible reverse e_ect, it is desirable to work with thin _lm thicknesses. A high quality 20 nm thick YIG _lm was grown by pulsed laser deposition, showing a damping similar to that of bulk YIG. We use nano-lithography to pattern series of YIG(20nm) and YIG(20nm)jPt(13nm) discs with diameters between 300 and 700 nm. The ferromagnetic resonance (FMR) spectra of the individual sub-micron sized samples are recorded through magnetic resonance force microscopy. . Passing dc-current through micron sized YIGjPt disks reveal a variation of the FMR linewidth consistent with the geometry and amplitude of the expected SHE transfer torque. In the absence of exciting microwave _elds, a variation in the magnetization is detected when the dc-current reaches the expected threshold for auto oscillations.

Ce travail concerne l'étude et la réalisation de dispositifs hyperfréquences coplanaires de type composite main droite/gauche (CRLH). Dans la première partie du mémoire, l'état de l'art des structures CRLH et leur aspect théorique sont présentés. La deuxième partie concerne la modélisation circuit et la conception de la cellule CRLH de base. Un modèle circuit a été développé à partir des modèles existants. Un résonateur d'ordre zéro (ZOR en anglais) à couplage capacitif a été fabriqué et les résultats expérimentaux nous ont permis de valider le modèle théorique. Une réduction de 80% de la taille du résonateur a été observée par rapport au résonateur demi-longueur d'onde à la même fréquence du travail. Une ligne de transmission à deux bandes de propagation a été réalisée par la mise en cascade de cinq cellules CRLH de base. La troisième partie est vouée à l'utilisation des couches magnétiques dans les structures CRLH pour réaliser des dispositifs hyperfréquences accordables. L'agilité en fréquence du ZOR a été confirmée expérimentalement. Nous avons aussi proposé un modèle théorique simple de la cellule CRLH réalisée sur un substrat de YIG. Les résultats expérimentaux de la ligne CRLH à ferrite et pour différentes valeurs du champ magnétique appliqué sont présentés et comparés au modèle théorique et aux simulations 3D.

Endonuclease II (EndoII) of bacteriophage T4 is a GIY-YIG enzyme involved in host DNA breakdown during phage infection of E. coli. EndoII combines features of restriction endonucleases with those of homing endonucleases in that it breaks down DNA foreign to itself but recognizes a 16 bp long asymmetric and ambiguous sequence. This investigation addresses the biological function of EndoII, its mode of interaction with its substrate and roles of individual residues in catalysis, sequence recognition and binding. It is shown here that EndoII increases the frequency of non-homologous recombination in phage-infected cells, showing that EndoII indeed can induce recombinational events. Although single-stranded nicks are frequent in in vitro reactions with purified protein, the enzyme is found to produce mostly double-stranded breaks in vivo, since nicks are repaired. Mutations of residues positioned on the putative catalytic surface result in severely reduced catalytic activity, while residues in the N-terminal region and a middle region (MR) appear to mainly contribute to substrate binding. Mutation of the putatively magnesium-binding residue E118 renders the enzyme catalytically inactive. Residues K76 (in the MR and positioned on the catalytic surface) and G49 and R57 (on the catalytic surface) also contribute to substrate recognition. All mutants bind as tetramers to two DNA molecules, indicating that the wildtype would also bind as a tetramer. EndoII E118A alone can bind also in monomeric and dimeric form to one DNA molecule, possibly because the glutamate charge normally repels the DNA. The solved crystal structure of tetrameric EndoII E118A shows a striking X-shape with two putative catalytic surfaces to each side positioned so that double-stranded cleavage would require severe DNA distortion. Combination of all data suggests that upon binding in vivo EndoII scans the DNA for a second binding site, binding to both sites but nicking or cleaving only one of them.

Homing endonucleases (HEs) typically have one of four types of catalytic domains (LAGLIDADG, GIY-YIG, H-N-H, His-Cys), and a DNA-binding region(s) that provides specificity. I-CreII, which is encoded by the psbA4 intron from Chlamydomonas reinhardtii, is unusual in containing two catalytic motifs: H-N-H and GIY-YIG. A previous study showed that I-CreII cleavage leaves 2-nt 3' OH overhangs similar to GIYYIG endonucleases, but that it also has a flexible metal requirement like H-N-H enzymes. Also, alanine substitution of several conserved residues in the GIY-YIG motif and two in the H-N-H motif did not produce a clear catalytic mutant, although some variants had strongly reduced DNA binding. Thus, in order to identify the catalytic motif, I substituted additional amino acids in both domains with alanine, and identified three histidines in the H-N-H motif that are likely to be involved in catalysis. To gain insight into how I-CreII interacts with its ~30-bp homing-site DNA, three types of DNA protection analysis were performed. Hydroxyl-radical footprinting, which reveals regions of tight DNA binding, indicated that I-CreII binds strongly to a region downstream of the cleavage and intron-insertion sites, corresponding to bp 2-10 of exon 5. There was also partial protection around the cleavage site, but only on the top strand, which is consistent with the enzyme's tendency to cleave this strand first. DNase I protection, which can reveal less closely-bound regions of target DNA, gave a larger footprint than hydroxyl-radical protection, with the additional region lying upstream of the cleavage site. These results also suggest that DNA backbone-binding downstream of the cleavage site involves sugars and phosphates, whereas upstream it is mainly with phosphates. DMS protection, which probes guanines on the N-7 position in the major groove, did not provide any evidence of major groove binding (at least not through guanines). DNase I protection could also be performed on the I-CreII variants that had reduced DNA affinity. The N161A variant was instructive in that it showed reduced protection of a T-A bp very close to the cleavage site, providing support for a catalytic role for the H-N-H motif and a possible constraint for modeling. Of the GIY-YIG motif variants, the footprint of the G231E/K245A variant was distinctly useful in that it was preferentially effected downstream of the cleavage site. This result suggested the H-N-H and GIY-YIG motifs are co-linear with their targets in the homing site. Structural modeling of the GIY-YIG domain of I-CreII using the solved I-TevI domain as template provided evidence for a unique insertion in the I-CreII structure that disrupted a catalytic α-helix; the insertion is predicted to be a positively charged, hairpinlike loop anchored by two antiparallel β-strands. I propose that this insertion can explain the evolutionary conversion of this catalytic endonuclease domain into a DNA-binding domain. These findings should also help to understand other dual-motif H-N-H/GIY-YIG endonucleases, such as I-CmoeI.

Les récents progrès dans les télécommunications exigent de nouveaux composants pouvant fonctionner à des fréquences de plus en plus élevées et l’électronique d’une manière générale exige des composants de très bonne qualité. L’objectif principal de ce travail est la conception, la réalisation et la caractérisation d’une micro-inductance intégrée utilisant les propriétés d’une couche relativement épaisse de matériau magnétique. Les structures bobinées étant difficilement intégrables, une structure planaire a été retenue. Deux types de dispositifs ont été réalisés : une structure composée d’une spirale sur une couche de matériau magnétique et une autre constituée d’une spirale prise en sandwich entre deux couches de matériau magnétique. Les études réalisées par simulation montrent de très bons résultats confirmés par les caractérisations. Plusieurs essais de caractérisation hautes fréquences (à l’aide d’un analyseur vectoriel) et basses fréquences (à l’aide d’un LCRmètre) ont été réalisés. Les résultats montrent un gain en termes de valeur d’inductance d’un facteur de deux sur la structure une couche et un gain d’un facteur proche de la perméabilité du matériau pour une structure double couche. Par ailleurs, une technique de caractérisation "courant fort" utilisant un té de polarisation et une technique de détermination de la perméabilité du matériau magnétique utilisant la combinaison des résultats de mesure et de simulation ont été développées. L’intégration des composants passifs comme l’inductance à couche magnétique relativement épaisse est possible grâce à l’utilisation des techniques de la microélectronique et de micro-usinage / Recent advances in telecommunications require new components that can operate at high frequencies and now, electronic requires high quality components. The main purpose of this work is the design, micro-fabrication and characterization of a micro-integrated inductor using properties of a relatively thick layer of magnetic material. As coiled structures are difficult to integrate a planar structure was chosen. Two kinds of devices have been made: a device consisting of one spiral on a layer of magnetic material and another consisting of one spiral sandwiched between two layers of magnetic material. The simulation studies show very good results confirmed by characterizations. Several high frequencies (using a vector analyzer) and low frequencies (using a LCRmeter) characterizations were made. Results show that the inductance value is multiplied by two in the case of a structure with one layer of magnetic material and by a factor close to the permeability of magnetic material in the case of a double layer structure. In addition, a high current characterization technique using a bias tee and a technique for determining the permeability of the magnetic material using a combination of measurement results and simulation have been implemented. The integration of passive components such as inductor with relatively thick magnetic layers is made possible by the use of microelectronic and micro-machining techniques

This work presents a survey of blue-stain fungi found in Northwestern Ontario, characterization of a homing endonuclease gene within Grosmannia piceiperda and finally an examination of the introns and homing endonuclease genes found in the large ribosomal subunit gene in species of Ceratocystis; using molecular techniques and phylogenetic analysis, we studied the molecular evolution of these mobile genetic elements. The blue-stain fungi of Northwestern Ontario were identified based on phylogenic analysis of rDNA internal transcribed spacer region sequences. This data was supplemented with morphological characteristics of the fungal cultures. The second project was an examination of a LAGLIDADG homing endonuclease and its IC2 group I intron. This intron is uniquely positioned within the group I intron-encoded rps3 gene of the large subunit ribosomal RNA gene. The final chapter is an investigation of the large subunit ribosomal RNA gene in species of Ceratocystis. The 3’ segment of this gene contains several novel introns and homing endonuclease genes. There is also much diversity between strains despite their close relation on the rDNA internal transcribed spacer region phylogenetic tree. Further, our data also suggest that the single motif LAGLIDADG homing endonuclease of the rDNA mL1923 intron is likely to be an ancestor to other homing endonucleases in the area. The results of these studies demonstrate the role that these elements play in the genetic diversity observed in the blue-stain fungi.

This work presents a survey of blue-stain fungi found in Northwestern Ontario, characterization of a homing endonuclease gene within Grosmannia piceiperda and finally an examination of the introns and homing endonuclease genes found in the large ribosomal subunit gene in species of Ceratocystis; using molecular techniques and phylogenetic analysis, we studied the molecular evolution of these mobile genetic elements. The blue-stain fungi of Northwestern Ontario were identified based on phylogenic analysis of rDNA internal transcribed spacer region sequences. This data was supplemented with morphological characteristics of the fungal cultures. The second project was an examination of a LAGLIDADG homing endonuclease and its IC2 group I intron. This intron is uniquely positioned within the group I intron-encoded rps3 gene of the large subunit ribosomal RNA gene. The final chapter is an investigation of the large subunit ribosomal RNA gene in species of Ceratocystis. The 3’ segment of this gene contains several novel introns and homing endonuclease genes. There is also much diversity between strains despite their close relation on the rDNA internal transcribed spacer region phylogenetic tree. Further, our data also suggest that the single motif LAGLIDADG homing endonuclease of the rDNA mL1923 intron is likely to be an ancestor to other homing endonucleases in the area. The results of these studies demonstrate the role that these elements play in the genetic diversity observed in the blue-stain fungi.

This thesis deals with the subject of fibre optic magnetic field sensors utilizing iron garnet materials. Such materials exhibit a large Faraday rotation which make them advantageous for application in compact mag­netic field sensors. After an introduction, in which fibre optic sensors and optical methods to measure electric current are reviewed, the original research work is summarized. A system for the measurement of the magneto-optic properties of trans­parent materials is described. Measurement results, showing the influence of temperature, magnetic field direction and sample treatment on the magneto-optical proper­ties of YIG-crystals, are presented. The proper­ties of thin magneto-optical waveguiding films have also been studied using different light coupling methods. Measurement results obtained for holo­graphic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. It is shown that the launching method may affect the properties to be measured. The design and performance of several versions of extrinsic guided wave fibre optic magnetic field sensors are then reported. The sensors employ substi­tuted YIG (Yttrium Iron Garnet, Y3Fe5O12) thin film waveguides as sensing elements. Polari­zation maintaining fibres were used as feed and return to provide two signal channels. The signals were combined in a balanced measure­ment system, providing insensitivity to both fluctuations in optical power and loss. Sensors have been made both with separate fibres to guide the light to and from the sensing element and with a single fibre for both functions. The two fibre version, although less ”elegant”, is found to have a better performance. This version also makes it possible to determine both the magnitude and sign of the magnetic field. Measurement results indicate a usable measurement range of at least several mT with a noise equivalent magnetic field level of less than 8 nT/root(Hz). The design and performance of multimode fibre optic magnetic field sensors utilizing the Faraday effect in an epitaxially grown thick (YbTbBi)IG film is also described. This type of sensor is found to be linear over a range from 27 mT to less than 270 nT. Sensor prototypes suitable for current monitoring in high voltage transmission lines have also been developed. / QC 20111209 / YIG

No description available.