Thèses : « Muon Spin Relaxation spectroscopy »

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Sadrollahi, Elaheh [Verfasser], et F. J. [Akademischer Betreuer] Litterst. « Fe1-xCuxCr2S4 Studied by Mössbauer Spectroscopy and Muon Spin Rotation and Relaxation / Elaheh Sadrollahi ; Betreuer : F. J. Litterst ». Braunschweig : Universitätsbibliothek Braunschweig, 2018. http://d-nb.info/1174702427/34.

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Kamusella, Sirko [Verfasser], Hans-Henning [Akademischer Betreuer] [Gutachter] Klauß et Vadim [Gutachter] Ksenofontov. « Electronic phase diagrams and competing ground states of complex iron pnictides and chalcogenides : A Mössbauer spectroscopy and muon spin rotation/relaxation study / Sirko Kamusella ; Gutachter : Hans-Henning Klauß, Vadim Ksenofontov ; Betreuer : Hans-Henning Klauß ». Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/112910513X/34.

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Goltz, Til. « On the electronic phase diagram of Ba1-xKx(Fe1-yCoy)2As2 and EuFe2(As1-xPx)2 superconductors ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-192059.

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In this thesis, I study the electronic and structural phase diagrams of the superconducting 122 iron pnictides systems Ba1-xKx(Fe1-yCoy)2As2 and EuFe2(As1-xPx)2 by means of the local probe techniques 57Fe Mössbauer spectroscopy (MS) and muon spin relaxation (muSR). For both isovalent substitution strategies - Co/K for Fe/Ba and P for As, respectively - the antiferromagnetic Fe ordering and orthorhombic distortion of the parent compounds BaFe2As2 and EuFe2As2 are subsequently suppressed with increasing chemical substitution and superconductivity arises, once long-range and coherent Fe magnetic order is sufficiently but not entirely suppressed. For Ba1-xKx(Fe1-yCoy)2As2 in the charge compensated state (x/2=y), a remarkably similar suppression of both, the orthorhombic distortion and Fe magnetic ordering, as a function of increasing substitution is observed and a linear relationship between the structural and the magnetic order parameter is found. Superconductivity is evidenced at intermediate substitution with a maximum Tsc of 15 K coexisting with static magnetic order on a microscopic length scale. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to nonmagnetic impurities to a system with a constant charge carrier density. Within this model, the experimental findings are compatible with the predicted s± pairing symmetry. For EuFe2(As1-xPx)2, the results from 57Fe MS and ZF-muSR reveal an intriguing interplay of the local Eu 2+ magnetic moments and the itinerant magnetic Fe moments due to the competing structures of the iron and europium magnetic subsystems. For the investigated single crystals with x=0.19 and 0.28, 57Fe MS evidences the interplay of Fe and Eu magnetism by the observation of a transferred hyperfine field below Tafm at which the Eu subsystem orders into a canted A-type AFM magnetic structure. Furthermore, an additional temperature dependent out-of-plane tilting of the static Fe hyperfine field is observed below the onset of static Eu ordering. ZF-muSR shows a strong increase of the local field at the muon site below Tafm=20 K and a crossover from isotropic to anisotropic Eu spin-dynamics between 30 and 10 K. The temperature dependence of the spin dynamics, as derived from the muSR dynamic relaxation rates, are related to a critical slowing down of Eu-spin fluctuations which extends to even much higher temperatures (~100 K). They also effect the experimental linewidth observed in the 57Fe MS experiments. The strong influence of the Eu magnetic order onto the primary observables in both methods prevents conclusive interpretation of the experimental data with respect to a putative interplay of Fe magnetism and superconductivity.

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Goltz, Til [Verfasser], Hans-Henning [Akademischer Betreuer] Klauß et Jörg [Akademischer Betreuer] Fink. « On the electronic phase diagram of Ba1-xKx(Fe1-yCoy)2As2 and EuFe2(As1-xPx)2 superconductors : A local probe study using Mössbauer spectroscopy and Muon Spin Relaxation / Til Goltz. Betreuer : Hans-Henning Klauß. Gutachter : Jörg Fink ». Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1083463098/34.

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Steele, Andrew J. « Quantum magnetism probed with muon-spin relaxation ». Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:030d7e91-f38e-433f-9539-652b0f4996cc.

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This thesis presents the results of muon-spin relaxation (µ⁺SR) studies into magnetic materials, and demonstrates how these results can be exploited to quantify the materials’ low moments and reduced dimensionality. Dipole-field simulations, traditionally used to estimate likely muon sites within a crystal structure, are described. A novel Bayesian approach is introduced which allows bounds to be extracted on magnetic moment sizes and magnetic structures—previously very difficult using µ⁺SR—based on reasonable assumptions about positions in which muons are likely to stop. The simulations are introduced along with relevant theory, and MµCalc, a platform-independent program which I have developed for performing the calculations is described. The magnetic ground states of the isostructural double perovskites Ba₂NaOsO₆ and Ba₂LiOsO₆ are investigated with µ⁺SR. In Ba₂NaOsO₆ long-range magnetic order is detected via the onset of a spontaneous muon-spin precession signal below T_c = 7.2(2) K, while in Ba₂LiOsO₆ a static but spatially-disordered internal field is found below 8 K. Bayesian analysis is used to show that the magnetic ground state in Ba₂NaOsO₆ is most likely to be low-moment (˜ 0.2µ_B) ferromagnetism and not canted antiferromagnetism. Ba₂LiOsO₆ is antiferromagnetic and a spin-flop transition is found at 5.5 T. A reduced osmium moment is common to both compounds, probably arising from a combination of spin–orbit coupling and frustration. Results are also presented from µ⁺SR investigations concerning magnetic ordering in several families of layered, quasi–two-dimensional molecular antiferromagnets based on transition metal ions such as S = ½ Cu²⁺ bridged with organic ligands such as pyrazine. µ⁺SR allows us to identify ordering temperatures and study the critical behaviour close to T_N , which is difficult using conventional probes. Combining this with measurements of in-plane magnetic exchange J and predictions from quantum Monte Carlo simulations allows assessment of the degree of isolation of the 2D layers through estimates of the effective inter-layer exchange coupling and in-layer correlation lengths at T_N. Likely metal-ion moment sizes and muon stopping sites in these materials are identified, based on probabilistic analysis of dipole-fields and of muon–fluorine dipole–dipole coupling in fluorinated materials.

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Aston, Georgina Margaret. « Molecular dynamics with muon spin relaxation/rotation ». Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338062.

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Willis, Maureen. « Muon spin relaxation as a probe of electron spin relaxation in organic semiconductors ». Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/5392.

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The purpose of this thesis is to study the electron spin relaxation (eSR) in small organic molecular semiconductors using the muon spin relaxation (MuSR) technique. One of the inherent problems in utilising the spin degree of freedom is the lack of understanding of the fundamental mechanisms behind spin relaxation. Two interactions have been proposed as the dominant mechanisms behind the spin relaxation, the Hyper ne interaction (HFI) and the Spin Orbit (SO) interaction. There remains much debate over the models for these interactions and their exact role, a contention that drives the work carried out in this thesis. The MuSR technique is utilised providing a novel molecular scale probe sensitive to relaxation rates in the range of 0.01-10 MHz. The Avoided Level crossing (ALC) MuSR application is useful in accessing the spin relaxation information. Temperature dependent ALC-MuSR measurements are performed for a selection of functionalised acenes and Quinolate molecules. Transverse eld MuSR measurements are also taken to determine the Hyper ne coupling constants present. DFT and semi-empirical computational methods are employed to determine theoretical values for the isotropic and anisotropic terms and the suitability of these methods was discussed. It is concluded that an intra-molecular eSR is present in all small organic molecular semiconductors. The mechanism behind this eSR was found not to be the HFI but in fact the SO interaction. It is also determined that the eSR is coupling to the vibrations in the molecule and a possible theory based on the curvature of the molecule from the vibrational modes inducing an enhanced SO coupling is proposed, which results in the eSR. The nal part of this thesis looks at the future experiments that have been initiated or can be conducted to further the understanding of spin relaxation and determine the role of a vibrationally enhanced SO coupling.

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Williams, Robert Charles. « Correlated magnetic oxides studied using muon-spin spectroscopy ». Thesis, Durham University, 2016. http://etheses.dur.ac.uk/11566/.

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This thesis is concerned with the application of muon-spin spectroscopy (muSR) in the study of correlated magnetic oxides. The results of four studies are presented, where muSR is used to provide insight into both the static and dynamic magnetic behaviours of the materials in question. The results of muSR measurements on the double perovskite compounds Sr2BOsO6 (B = Co, Fe, Y, In) are presented. The Co compound exhibits lattice-site-specific ground states and spin dynamics with two distinct, partially ordered antiferromagnetic states encountered upon cooling from room temperature. Here, and also for the Fe compound, the muSR results reveal the evolution of the internal fields through the phase transitions and as dynamic relaxation channels freeze out on further cooling. The possibility of incommensurate magnetic ordering is considered for the Y and In compounds. The magnetic properties of the tetrahedral spin-chain oxide CsCoO2 are investigated using muSR, with results that are consistent with a magnetic structure comprising ferromagnetically ordered Co-Co spin dimers, themselves arranged in antiferromagnetic chains. The critical behaviour near TN and the magnetostructural coupling in the vicinity of a structural phase transition are examined. These results help elucidate a complex freezing out of relaxation processes upon cooling, induced by a bifurcation of superexchange bond angles. A revised magnetic phase diagram is reported for the antiferromagnetic insulating series L(2-x)Sr(x)CoO4, which has been shown to support charge ordered and magnetic stripe phases and an hourglass magnetic excitation spectrum. It is found that the suppression of the magnetic ordering temperature is highly sensitive to small concentrations of holes. Distinct behaviour within an intermediate x range suggests that the putative stripe ordered phase extends to lower x than previously thought, whereas further charge doping prevents magnetic ordering for T > 1.5 K. Finally, the results of the first transverse field muSR measurements to be made on a skyrmion lattice phase are presented. The muon response to that phase and the surrounding ones within Cu2OSeO3 is used to demonstrate how the technique is sensitive to the skyrmion lattice via the frequency domain lineshape.

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Lancaster, Tom. « Muon-spin relaxation and its application to magnetic systems of differing dimensionality ». Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409811.

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Shermadini, Zurab. « Iron based pnictide and chalcogenide superconductors studied by muon spin spectroscopy ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-148934.

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In the present thesis the superconducting properties of the Iron-based Ba_{1-x}Rb_{x}Fe_{2}As_{2} arsenides, and A_{x}Fe_{2-y}Se_{2} (A = Cs, Rb, K) chalcogenides are investigated by means of Muon Spin Rotation Spectroscopy. The temperature and pressure dependence of the magnetic penetration depth is obtained form muSR experiments and analyzed to probe the superconducting gap-symmetries for each samples. The Ba_{1-x}Rb_{x}Fe_{2}As_{2} system is described within the multi-gap s+s-wave scenario and results are discussed in the light of the suppression of inter-band processes upon hole doping. Due to the lowered upper critical field Bc2 and reduced Tc, a large section of B-T-p phase diagram is studied for the hole-overdoped x=1 case. By applying hydrostatic pressure, the RbFe_{2}As_{2} system exhibits a classical BCS superconducting characteristics. The A_{x}Fe_{2-y}Se_{2} chalcogenide represents a system containing magnetically ordered and superconducting phases simultaneously. In all investigated chalcogenide samples, about 90% of the total volume show the strong antiferromagnetic phase and 10% exhibit a paramagnetic behavior. Magnetization measurements reveal a 100% Meissner effect, while muSR clearly indicates that the paramagnetic phase is a perfect superconductor. Up to now, there is no clear evidence whether the antiferromagnetic phase is also superconducting. The microscopic coexistence and/or phase separation of superconductivity and magnetism is discussed. Moreover, a new hydrostatic double-wall pressure cell is developed and produced, satisfying the demands of muSR experiments. The designs and characteristics of the new pressure cell are reviewed in the present thesis.

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Chen, Karen. « Studies on LiYRF ». Thesis, Boston College, 2010. http://hdl.handle.net/2345/1561.

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Thesis advisor: Michael Graf
Senior thesis on muon spin relaxation study of LiHoXY1-XF4 and semi-adiabatic specific heat experiment on LiTb0.40Y0.60F4
Thesis (BS) — Boston College, 2010
Submitted to: Boston College. College of Arts and Sciences
Discipline: Physics Honors Program
Discipline: Physics

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Möller, Johannes S. « Muon-spin relaxation and its application in the study of molecular quantum magnets ». Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:7f19318c-a78e-4499-803b-b93df5ee169a.

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This thesis is concerned with the muon-spin relaxation (musr) technique and its application in the study of a number of molecular magnetic systems that may be driven through a quantum phase transition at low temperatures through the application of a magnetic field or hydrostatic pressure. Musr is a highly sensitive probe of magnetism, but its utility can be severely limited by the lack of knowledge of the muon implantation site and the extent to which the muon perturbs its host. In a system of ionic fluorides, where partial information about the muon site is experimentally available, I demonstrate systematically that these problems can be addressed accurately using electronic-structure calculations. The F--$mu$--F complex formed by muons in many fluorides can be understood as an exotic molecule-in-a-crystal defect with a zero-point energy larger than that of any naturally-occurring triatomic molecule. I demonstrate the interesting possibility of controlling the magnetic dimensionality in a molecular magnet using applied pressure. musr and high-field magnetisation experiments under applied pressure on the coordination polymer CuF$_2$(H$_2$O)$_2$(pyrazine) show a transition from a quasi-two-dimensional to a quasi-one-dimensional antiferromagnetic phase. Density-functional theory calculations and calculations of the dipolar anisotropy complement the experiments. I describe how subtle differences in chemical composition can lead to starkly different structural and magnetic properties. [Cu(pyz)(H$_2$O)(gly)$_2$](ClO$_4$)$_2$ may be considered an antiferromagnetic chain that orders below 50 mK while the related compound [Cu(pyz)(gly)](ClO$_4$) is formed from Cu$^{2+}$ dimers and remains disordered down to 30 mK in zero field, but displays a field-temperature phase diagram consistent with the Bose-Einstein condensation of triplons. I also describe musr measurements on the strong-leg spin ladder DIMPY and on the molecular nanomagnets Cr$_8$Cd and Cr$_8$Mn which highlight some of the remaining challenges for longitudinal-field musr experiments.

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Lang, Franz. « Muon-spin relaxation and density functional techniques in the study of novel magnetic systems ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:869b716e-2a12-468b-a031-9bfd0078cdaa.

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The main focus of this thesis is the experimental muon-spin relaxation technique (μ+SR) and its application to study novel and unconventional magnetic behaviour. I present a range of experimental measurements which I supplement with theoretical calculations to remove the two main limitations inherent to μ+SR and thereby improve the understanding of the experimentally observed behaviour. Additionally, I investigate the potential effects of demagnetising fields on highfield μ+SR measurements. μ+SR employs positively charged muons as sensitive local magnetic probes but has the essential drawback that there is normally a lack of knowledge about where the muons implant in a given sample and the extent of subsequent local distortions. In some cases this nescience makes interpretation of μ+SR data very challenging and severely limits the conclusions that can be drawn. Two research projects presented in this thesis are centred around utilising ab initio structural calculations based on density functional theory in order to remove these two inherent limitations of μ+SR and gain insights into the stopping sites of the muons and their local environments. In the case of the Pr based pyrochlores Pr2B2O7 (B=Sn, Hf, Zr, Ir) I combine such ab initio computations of the muon sites with calculations of the crystalfield levels of the Pr3+ ions. I demonstrate that the non-Kramers doublet ground state of the Pr ions is split due to the presence of the muons and that this consequently results in a hyperfine enhancement of the Pr nuclear moments. By showing the theoretically calculated values of the ground state splittings to be in fair agreement with those obtained from fits to the experimental data, I demonstrate that the μ+SR measurements of Pr2B2O7 re ect muon induced effects rather than intrinsic behaviour. I subsequently investigate the conceptually very similar spin ices A2Ti2O7 (A= Dy, Ho) using the same methodology and confirm that in this case the muons act as passive probes. A second project presented in this thesis concerns the compound a-RuCl3, in which Ru ions form nearly perfect two-dimensional honeycomb layers. The experimental μ+SR data reveal two magnetic phase transitions, the origins of which I study by combining calculations of the potential muon sites with computations of the dipolar fields experienced by the muons at these sites for different magnetic structures. I show that the experimental observations are only fully explained through a temperature regime between the two measured transitions in which the Ru spins share significant correlations within the honeycomb layers but not between the separate layers. A final research aspect I present is a study of the potential effects of demagnetising fields in high field μ+SR measurements. I derive an analytical solution for the demagnetising tensor of a uniformly magnetised finite cylinder and use it to show that edge regions of a sample suffer the most from demagnetising effects. I subsequently discuss the resulting experimental signatures and methods to identify and reduce them.

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Yen, Hon Kit. « Theoretical spin dynamics on muonium level-crossing resonance ». Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28531.

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Redfield's theory and the theory of master equations have been reviewed and their applications to muonium spin dynamics discussed. It was found that both theories are equivalent in the Markov limit. In some cases, analytical expressions for relaxation rates are found. In addition, Redfield's theory was applied to describe spin relaxation of muonium-substituted free radicals near level-crossing resonances. Theoretical predictions were compared with experimental data for the C₆F₆-Mu radical and the results suggest there are several relaxation mechanisms involved.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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Disseler, Steven Michael Thomas. « Magnetic Order in the Pyrochlore Iridates ». Thesis, Boston College, 2013. http://hdl.handle.net/2345/3148.

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Thesis advisor: Michael J. Graf
This thesis is concerned with experimentally determining the magnetic and electronic states in a unique class of transition metal oxides known as the pyrochlore iridates, A₂Ir₂O₇ (A = Y or Rare earth). The extended nature of the 5d Ir orbitals in the iridates places these materials in a regime of intermediate electron correlation and large spin-orbit interaction such that this system may host several novel or topological states of matter which may be perturbed by incorporating different A-species. Additionally, the pyrochlore structure is geometrically frustrated and has been long been studied as a potential host of a number of exotic magnetic phenomenon. However, even after years of intense theoretical and experimental interest many fundamental questions still remain about the nature of the magnetic ground sates in this series which are of vital importance in understanding the roles of various interactions and potential of such novel phenomenon. The primary aim of this thesis is therefore to determine how magnetic order develops on the Ir sublattice in this series, particularly how it is perturbed through variation of the crystalline structure, magnetism of the A-site ions, and presence of mobile charges. This thesis is the first comprehensive experimental study of these effects which has utilized several complementary experimental probes of both bulk and local magnetism in a number of compounds. The techniques presented in this work include magnetotransport, bulk magnetization, elastic neutron scattering, and muon spin relaxation (µSR) measurements. All of the three compounds studied in this work (A = Y, Yb, and Nd) are shown to definitively exhibit long-range magnetic order on the Ir sublattice, which has previously only been inferred based on studies of other compounds. The compounds Y₂Ir₂O₇ and Yb₂Ir₂O₇ are correlated insulators at low temperature and are found to have identical configuration of the Ir moments, despite the presence of the large localized Yb³⁺. Numerical investigations presented here have provided the first conclusive evidence that this order is of the `all-in/all-out' type, consistent with recent resonant x-ray studies; additionally, we have shown that this order exists for all insulating compounds regardless of structural parameters or properties of the A-ion. On the other hand, Nd₂Ir₂O₇ is weakly metallic with Kondo-like behavior at low temperature, with long-range order only on the Ir site, in disagreement with previous results from neutron scattering. Measurements of the field dependent magnetization and Hall effect reveal a large anomalous Hall component, suggesting that the Nd3+ may exhibit a spin-ice state with very short correlation length, while the Ir sublattice is likely in the `all-in/all-out' state. From this, it is determined that Nd₂Ir₂O₇ lies at an important cross-over point in the series in which correlation energy and conduction bandwidth yield chiral order with features akin to both the metallic unordered Pr₂Ir₂O₇ and those of the magnetically ordered insulators. These results are discussed with regard to recent theoretical models exploring the role of electron correlation, frustration and various exchange interactions in these materials
Thesis (PhD) — Boston College, 2013
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

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Jestadt, Thomas. « Muon studies of low-dimensional solid state systems ». Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301173.

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Creamer, N. J., L. E. Macaskie, P. Mikheenko, I. P. Mikheenko, S. P. Cottrell et A. R. Williams. « Observation of the Curie Transition in Palladium Bionanomaterial Using Muon Spin Rotation Spectroscopy ». Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35339.

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Palladium bionanomaterial was manufactured using the sulfate-reducing bacterium, Desulfovibrio desulfuricans, to reduce soluble Pd(II) ions to cell-bound Pd(0). The material was examined using a Superconducting Quantum Interference Device (SQUID) to observe bulk magnetisation over the temperature range 10 – 300 K and by Muon Spin Rotation (μSR), which is a probe of the local magnetic environment inside the sample, over the temperature range 200 – 700 K. Results from SQUID were used to model the temperature dependence of ferromagnetic and paramagnetic components of the bulk magnetisation and, by extrapolation, to predict the Curie transition temperature. Results from μSR confirmed the accuracy of the prediction to within 20 K. The Curie transition, which started at 528 K, was shown to be spread over a wide ( 100 K) range. This was attributed to dependence of the transition on particle size and the range of particle sizes in the population. A competing contribution to the overall magnetisation was observed due to partial thermal decomposition of the organic component of the material. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35339

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Wenner, Sigurd. « Transmission electron microscopy and muon spin relaxation studies of precipitation in Al–Mg–Si alloys ». Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23701.

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The Al–Mg–Si system is a heat-treatable class of aluminium alloys that gain their mechanical strength via precipitation hardening. The main hardening phases are precipitated as needle-shaped nano-sized particles from a solid solution of Mg, Si and other added elements. Transmission electron microscopy and muon spin relaxation was used to study precipitation and clustering in Al–Mg–Si alloys, varying the heat treatment and chemical composition in order to understand the kinetics of precipitation and the morphology, distribution, and atomic structure of hardening precipitates. Muons were found to form bonds with vacancies, atoms in solid solution, and clusters of solute atoms, which are the defects we can gain information from by applying muon spin relaxation to Al alloys. In binary Al–Mg and Al–Si alloys, we discovered very different vacancy behaviours after cooling from high temperatures: Si–vacancy clusters are quickly formed at room temperature in Al–Si, while Al–Mg keeps a much higher vacancy content than pure Al and Al–Si despite a lack of solute clustering. A high muon trapping in a specific temperature range was found in a 1.6% Mg2Si alloy annealed for 16 hours at 70–150 °C. These conditions contain clusters and Guinier–Preston-zones preceding the main hardening phase beta'' in the precipitation sequence. Density functional theory calculations support that the relevant muon trapping site is vacancies inside these structures, suggesting that the structures are stabilised by absorbing vacancies during annealing. The roles of the elements Cu and Ca on precipitation during artificial ageing were investigated. Room temperature storage gives a negative effect on the strength of aged high-solute Al–Mg–Si alloys, in particular when the Mg/Si ratio is high. The negative effect was found to be diminished and delayed by adding 0.14 at.% Cu to alloys with Mg+Si = 1.3 at.%, in addition to giving an overall strength increase. Transmission electron microscopy investigations revealed that the fraction of Cu-containing precipitates increased with room temperature storage before ageing. The Cu addition is believed to help the formation of clusters that can act as nucleation sites for hardening precipitates and/or prevent the formation of clusters that can not. Various amounts of Ca was added to an alloy with 0.53% Mg and 0.40% Si. The Ca accumulated in large particles with composition CaAl2Si2, as determined by X-ray energy dispersive spectroscopy. The presence of Si in the particles causes a reduction of the available Si for precipitation and an increase in the effective Mg/Si ratio. The result is a coarser microstructure with a higher fraction of over-aged precipitates and a lower mechanical strength. Aberration-corrected scanning transmission electron microscopy coupled with electron energy loss spectroscopy was conducted on an over-aged Al–Mg–Si–Cu–Ag alloy. The microstructure consisted of mostly disordered L and Q' precipitates. After applying principal component analysis to the acquired spectrum images, atomic columns containing Cu and Ag could be clearly distinguished. Cu and Ag were seen to prefer different atomic configurations, and were not observed occupying the same columns. While Cu columns mostly resided in ordered parts of precipitates and along precipitate–matrix interfaces, Ag was diluted in several nearby columns in disordered parts, and at precipitate–matrix interfaces of high misfit.

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Foronda, Francesca. « Muon spin spectroscopy and high magnetic field studies of novel superconductors and magnetic materials ». Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:55c7ed6b-af31-4b7b-8b64-217dcc6846ac.

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This thesis investigates a number of novel magnetic materials and high temperature superconductors using high-field magnetometry and muon spin spectroscopy (μSR). The main measurement techniques are briefly described and a study of the dimer material [Cu(pyrazine)(glycine)]ClO₄ is presented to demonstrate the use of the proximity detector oscillator as a susceptometer in high magnetic fields. μSR is a highly effective tool for probing magnetic order, spin freezing and spin dynamics. However, in some circumstances its performance may be impaired by the extent to which it perturbs the material under study. Using μSR, density functional theory and crystal field calculations, I identify an experimental situation in the family of candidate quantum spin ices Pr₂B₂O₇ (B = Sn, Zr, and Hf), in which the measured response is dominated by a muon-induced distortion of the local structure. This issue is also addressed in a study of the spin dynamics in the canonical spin ice Ho2Ti2O7. Although computational work indicates a similar muon-induced effect in both Ho₂Ti₂O₇ and Dy₂Ti₂O₇, the μSR data is not dominated by this perturbation. The remainder of this thesis is concerned with studying the superconducting properties of a number of Fe-based materials, including LiFeP which is found to have an enhanced superfluid stiffness in relation to its transition temperature. Also reported is the effect of structural disorder on the superconducting state in recently discovered Sr_0.3(NH₂)_y(NH₃)_1-yFe₂Se₂. Pulsed magnetic field measurements are used to probe the temperature dependence of the upper critical field, giving a maximum value of μ₀H_c2(0)≈33(2) T. I also investigate the effect of intercalating additional ammonia, via reversible adsorption and desorption in the related superconductor Li_x[(NH₂)_y(NH₃)_1-y]_zFe₂Se₂ (z = 1, 2). These reactions were carried out in situ on the muon beamline so that the superfluid stiffness could be measured using transverse-field μSR on a single sample.

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Bertin, Alexandre. « Geometrical frustration and quantum origin of spin dynamics ». Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENY014/document.

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Cette thèse se concentre sur l'étude de composés magnétiques géométriquement frustrés où les ions magnétiques se situent aux sommets d'un réseau de tétraèdres partageant leurs sommets: les composés pyrochlores. Deux familles de formule chimique R2M2O7, où R est un lanthanide et M= Ti, Sn, sont particulièrement intéressantes puisqu'elles présentent une grande variété d'états magnétiques exotiques. Premièrement, nous avons étudié le champ cristallin agissant au site de la terre rare dans l'approximation de Stevens où uniquement le terme fondamental est considéré. Un jeu unique de paramètres a été déterminé pour chaque famille considérée grâce à une analyse globale incluant des spectres de neutrons inélastiques de plusieurs composés. Ensuite, nous avons caractérisé avec un large éventail de techniques les propriétés physiques à basse température de Nd2Sn2O7. En dessous de la température de transition Tc=0.91 K, ce composé possède un ordre magnétique à longue portée dans la configuration de spins dite "all-in-all-out". Une persistance de la dynamique de spins a été révélée dans la phase ordonnée, attribuée à des excitations unidimensionnelles de spins. Une dynamique de spins anormalement lente est également reportée dans la phase paramagnétique. Enfin, nous avons apporté quelques informations sur les deux états fondamentaux proposés pour le composé très étudié Tb2Ti2O7: premièrement, l'apparition d'une transition Jahn-Teller à basse température est suggérée mais l'absence d'élargissement des pics de Bragg réfute la présence d'une transition structurale. Enfin ce composé pourrait être un exemple d'une glace de spin quantique mais l'existence d'un plateau d'aimantation n'est pas évident jusqu'à T=20 mK
This Phd thesis focuses on the study of magnetically frustrated compounds where magnetic ions lie at the vertices of a corner-sharing tetrahedra network: the pyrochlore compounds. The two series of chemical formula R2M2O7, where R is a lanthanide and M=Ti, Sn, are of peculiar interest since they display a large variety of exotic magnetic ground states. First, we have studied the crystal-electric-field acting at the rare earth within the Stevens approximation where only the ground state multiplet is considered. A single set of parameters for each families of interest has been determined through a global analysis including several inelastic neutron scattering spectra of various compounds. Then, we have characterised with a large panel of techniques the low temperature physical properties of Nd2Sn2O7. This compound enters a long-range magnetic order at transition temperature Tc=0.91 K with an ``all-in-all-out'' spin configuration. A persistence of spin dynamics has been found in the ordered phase, ascribed to one-dimensional spin loops excitations. Anomalously slow paramagnetic spin fluctuations are also reported. Finally, we have brought information on the two proposed ground states of the widely studied compound Tb2Ti2O7: first, a Jahn-Teller transition is claimed to occur at low temperatures but no broadening of the Bragg peaks is seen down to T=4 K precluding premises of a structural transition. Secondly, this compound could be a realisation of a quantum spin-ice but no definitive evidence of a magnetisation plateau is found down to T=20 mK

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Hodges, Alex Randall. « EXCITON SPIN RELAXATION IN ZNMNSE-BASED DIULUTE MAGNETIC SEMICONDUCTOR HETEROSTRUCTURES ». University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin976201363.

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Groves, Ronald William. « O17 spin-lattice relaxation solid state NMR studies of pure and doped ices ». Columbus, Ohio : Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1021903674.

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Thesis (Ph. D.)--Ohio State University, 2002.
Title from first page of PDF file. Document formatted into pages; contains xx, 128 p.; also contains graphics. Includes abstract and vita. Co-advisors: Charles H. Pennington and James V. Coe, Dept. of Chemistry. Includes bibliographical references (p. 124-128).

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Karthik, G. « Investigations Of Spin-Dynamics And Steady-States Under Coherent And Relaxation Processes In Nuclear Magnetic Resonance Spectroscopy ». Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/259.

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The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by, (formula) where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3]. From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.

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Frassineti, Jonathan. « Evidence of a quantum entangled state between the muon spin and 51V nuclear spin (I=7/2) in A15 compounds ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.

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The purpose of this thesis is the study of the interaction at the atomic level between the positive muon μ+, with spin S = 1/2, and nuclei having spin I >1/2. Normally the μ+, a particle with a charge equal (in absolute value) to that of the electron and which interacts with the magnetic fields through its magnetic moment, can form a quantum entangled state when it is implanted between two nuclei with spin I=1/2, such as fluorine; this phenomenon causes a peculiar trend of the muon polarization. This phenomenon has never been observed for materials with nuclei having large spin. Very recently a similar phenomenon has been observed in a system containing Na (I= 3/2). Here we study a system with V which has larger nuclear spin I= 7/2. Nuclei with spin I >1/2 have a quadrupolar moment Q and can be subject to an electric field gradient (EFG) based on the symmetry of the crystal lattice. Furthermore, the muon itself induces an EFG within the crystalline structure, which combines with that, if present, generated by the material itself. This phenomenon has recently been observed in compounds with A15 crystal structure by using the muon resonance spectroscopy. These materials, with the chemical formula A3B (where A is a transition metal and B any other element), have type-II superconductivity but they do not exhibit magnetism. In this thesis we performed a study of V3B samples with B = Si, Sn, Ge by a) a structural characterization by a Rietveld analysis of high resolution X-rays Diffraction patterns, b) the data analysis of the muon polarization and a subsequent simulation of the latter.

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Gulener, Fatih. « Etude expérimentale et théorique de la relaxation des moments magnétiques dans un verre de spin Ising ». Phd thesis, Université Paris Sud - Paris XI, 2001. http://tel.archives-ouvertes.fr/tel-00001917.

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Nous étudions principalement les propriétés dynamiques dans le verre de spin quasi-Ising métallique FexTiS2 où les atomes de fer sont insérés par intercalation dans une structure en feuillets. Des mesures d'aimantation statique au SQUID et de caractérisation structurale par diffraction de rayons X (diagramme de poudre, affinement Rietveld) sont présentées afin de comprendre le diagramme de phase. Nous étudions la forme de la relaxation de spin en fonction de la température et de la concentration d'impuretés x. L'intérêt de travailler avec ce type de matériau très anisotrope est de se placer dans les conditions proches des modèles théoriques et des simulations numériques. Ceux-ci, en dessous de la température de gel Tg et à T = Tg, montrent une relaxation de forme algébrique. Afin de sonder la dynamique au-dessus de Tg, nous utilisons les techniques de spectroscopie de dépolarisation de muons (mSR) (pour x = 2, 3 et 5 %) et d'écho de spin de neutrons (NSE) (x = 20 et 36 %). Ces deux procédés d'investigation ensemble donnent accès à une fenêtre de temps qui va de la nanoseconde à la microseconde. Ils révèlent un caractère quasi-statique et une dynamique lente des spins sur une plage importante de température au-dessus de Tg. La forme de la fonction d'autocorrélation dynamique spin-spin q(t) est déterminée grâce à un modèle de dépolarisation de muons. L'analyse des spectres expérimentaux s'appuie sur la comparaison avec les courbes provenant de calculs numériques basés sur ce modèle ainsi que sur les ajustements effectués. Les résultats sont cohérents avec une l'existence fonction q(t) suivant la forme d'Ogielski. Le comportement thermique des paramètres microscopiques est en accord avec les simulations d'Ogielski sur des systèmes Ising 3D. Nous constatons une différence qualitative de la dynamique entre ce composé quasi-Ising et les composés Heisenberg AuFex et AgMnx. Pour ce dernier, l'observation des spectres de dépolarisation indique une relaxation quasi algébrique.

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Clark, Lucy. « Synthesis and study of frustrated oxide and mixed anion materials ». Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8073.

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Mixed anion systems, such as oxynitrides and oxyfluorides, are an emerging class of interesting materials. The lower stability of mixed anion systems in comparison to oxide materials has had the consequence that this area of materials research is relatively less well explored. However, the development of new synthesis techniques has resulted in the preparation of many new mixed anion systems and so a detailed understanding of their structure and how this relates to their electronic and magnetic properties is necessary. Within this Thesis, several oxide, oxynitride and oxyfluoride systems are investigated with a particular focus on the magnetic behaviour of materials based on geometrically frustrated pyrochlore and kagome lattices. The Lu2Mo2O7 pyrochlore contains a geometrically frustrated network of vertex sharing Mo4+ (d2 S = 1) tetrahedra. Here, the solid state synthesis of Lu2Mo2O7−x is reported along with a discussion of the coexistence of two cubic pyrochlore phases that has been discovered in samples synthesised at 1600 ◦C. Powder neutron diffraction and thermogravimetric analysis have revealed that this two-phase behaviour originates from a miscibility gap between stoichiometric Lu2Mo2O7 and oxygen deficient Lu2Mo2O6.6. Magnetic susceptibility and muon spin relaxation measurements support the formation of a geometrically frustrated spin glass ground state in Lu2Mo2O7 with a spin freezing temperature Tf ∼ 16 K. Low temperature neutron diffraction has confirmed the absence of long range magnetic order and magnetic diffuse neutron scattering data have indicated the presence of competing nearest and next nearest neighbour antiferromagnetic exchange interactions in the spin glass state. The magnetic heat capacity of Lu2Mo2O7 follows a T2-dependence at the low temperatures, indicating that Lu2Mo2O7 is another rare example of an unconventional, topological spin glass, which is stable in the absence of significant chemical disorder. The magnetic properties of the oxygen deficient pyrochlore phase Lu2Mo2O6.6 are qualitatively similar to those of Lu2Mo2O7, but an increase in the spin freezing temperature Tf ∼ 20 K suggests that oxygen-vacancy disorder in Lu2Mo2O6.6 favours the onset of a glassy state at higher temperatures and enhances the degree of frustration. Oxynitride pyrochlores with the ideal composition R2Mo2O5N2 (R = rare earth) contain Mo5+ d1 S = 1 2 cations on the frustrated pyrochlore lattice and are thus ideal candidates to support exotic magnetic ground states. Here, the synthesis of oxynitride pyrochlores of the Lu2Mo2O7 system by thermal ammonolysis is discussed alongside powder neutron diffraction and susceptibility data that show no evidence for long range magnetic order and an absence of spin freezing down to at least 2 K despite the persistence of strong antiferromagnetic exchange (θ = −120 K). A comparison of the magnetic diffuse neutron scattering between the spin glass state of Lu2Mo2O7 and the oxynitride is given, which suggests that the majority of the magnetic scattering in the oxynitride system is inelastic. In addition, low temperature magnetic heat capacity shows an absence of magnetic phase transitions and a continuous density of states through a T-linear dependence down to 500 mK. [NH4]2[C7H14N][V7O6F18], diammonium quinuclidinium vanadium(III,IV) oxyfluoride or DQVOF, is a kagome bilayer system with a geometrically frustrated two-dimensional kagome network of V4+ d1 S = 1 2 cations and V3+ d2 S = 1 cations between the kagome layers. Here, low temperature magnetisation and heat capacity data are presented, which demonstrate that the interplane V3+ d2 cations are well decoupled from the kagome layers at low temperatures such that DQVOF is a good experimental realisation of a S = 1 2 kagome antiferromagnet. Despite significant antiferromagnetic exchange (θ = −60 K) within the kagome planes, muon spin relaxation data have confirmed the absence of spin freezing and the persistence of internal field fluctuations that are intrinsic to the kagome layers down to temperatures of 40 mK. The low temperature heat capacity of the V4+ kagome network follows T-linear behaviour down to the 300 mK, highlighting the absence of a spin gap in the low energy excitation spectrum of DQVOF. The low temperature magnetic study of DQVOF presented here thus strongly supports the formation of a gapless quantum spin liquid phase. In the final results chapter, a discussion of the anion ordering principles in oxynitride systems is given. A high temperature, high resolution neutron diffraction study of the oxynitride perovskite SrTaO2N has revealed that the partial anion order that results in segregated Ta-N zig-zag chains is stable up to 1100 ◦C. Furthermore, these anion ordering principles are extended to the d1 perovskite oxynitrides RVO2−xN1+x (R = La, Nd, Pr) in a variable temperature neutron diffraction study, which confirms that the anion chain ordering discovered in d0 SrTaO2N is robust to electron doping. The R = La analogue also provides an interesting example of a rhombohedral oxynitride perovskite phase which coexists with an orthorhombic phase over the 4−300 K temperature range of the neutron diffraction study.

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Harvey, Pierre Dominique. « Applications of vibrational spectroscopy and NMR spin-lattice relaxation time measurements to organometallic and organic molecular crystals ». Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=73986.

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Beck, Michael [Verfasser]. « Optical spectroscopy of donor bound excitons and spin relaxation of donor electrons in isotopically enriched silicon / Michael Beck ». Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2019. http://d-nb.info/1194158439/34.

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Adur, Rohan. « Magnetic Coupling and Relaxation at Interfaces Measured by Ferromagnetic Resonance Spectroscopy and Force Microscopy ». The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406120604.

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Nordstierna, Lars. « Molecular Association Studied by NMR Spectroscopy ». Doctoral thesis, Stockholm : Physical Chemistry, Department of Chemistry, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3947.

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Ou, Yu-Sheng. « Ultrafast Study of Dynamic Exchange Coupling in Ferromagnet/Oxide/Semiconductor Heterostructures ». The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1490361750624291.

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Shermadini, Zurab [Verfasser], Hans-Henning [Akademischer Betreuer] Klauß et Clemens [Akademischer Betreuer] Laubschat. « Iron based pnictide and chalcogenide superconductors studied by muon spin spectroscopy / Zurab Shermadini. Gutachter : Hans-Henning Klauß ; Clemens Laubschat. Betreuer : Hans-Henning Klauß ». Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://d-nb.info/1068447737/34.

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Young, Matthew Alexander. « A site-directed spin labelling study of the human alpha-lactalbumin molten globule ». Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:cdc9904d-77cc-4d20-b01d-096bc2b16d72.

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The human α-lactalbumin (α-LA) molten globule formed at low pH is a model for the study of protein folding intermediates. The molten globule lacks native-like side-chain interactions, resulting in a fluctuating ensemble of tertiary structures, characterisation of which has been precluded by severe line-broadening in NMR spectra and a lack of long-range NOEs. Paramagnetic relaxation enhancements (PREs) have been measured in a variant of α-LA in which all native cysteines have been mutated to alanine (all-Ala α-LA). Cysteine residues have been mutated into regions of interest and spin labelled with MTSL. These measurements have confirmed that all-Ala α-LA forms a compact molten globule. Transient, long-range interactions that are stabilising the compact fold have also been identified using PREs measured in urea-denatured states. This has identified several interactions formed by hydrophobic residues from both the α- and β-domain, which could be important for initiating and driving folding. The molten globule’s 3D topology has been probed by measuring long-range distances between MTSL pairs using Double Electron-Electron Resonance (DEER). Broad distance distributions have been identified between elements of secondary structure, indicative of a fluctuating but compact fold. By contrast, a narrower distance distribution has been measured within one of the major helices, indicative of native-like secondary structure. The surface accessibility of all-Ala α-LA and that of two other variants ([28-111] α-LA and 4SS α-LA) has been probed using solvent PREs obtained using TEMPOL, a paramagnetic co-solute. This has revealed differences in the solvent-exposure of hydrophobic residues due to the removal of disulphide bonds. This method has also identified buried hydrophobic residues that contribute to forming the molten globule’s stable, native-like core.

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Ikeda, Atsutoshi. « Unconventional properties of the antiperovskite oxide superconductor Sr₃-xSnO and a related compound ». Kyoto University, 2020. http://hdl.handle.net/2433/253070.

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Bhowmick, Mithun. « Time Resolved Spectroscopy in InAs and InSb based Narrow-Gap Semiconductors ». Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/77136.

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As the switching rates in electronic and optoelectronic devices are pushed to even higher frequencies, it is crucial to probe carrier dynamics in semiconductors on femtosecond timescales. Time resolved spectroscopy is an excellent tool to probe the relaxation dynamics of photoexcited carriers; where after the initial photoexcitation, the nonequilibrium population of electrons and holes relax by a series of scattering processes including carrier-carrier and carrier-phonon scattering. Probing carrier and spin relaxation dynamics in InAs and InSb based narrow-gap semiconductors is crucial to understand the different scattering mechanisms related to the systems. Similar studies in InSb quantum wells are also intriguing, especially for their scientifically unique features (such as small effective mass, large g-factor etc). Our time resolved techniques demonstrated tunability of carrier and spin dynamics which might be important for charge and spin based devices. The samples studied in this work were provided by the groups of Prof. Wessels (Northwestern University) and Prof. Santos (University of Oklahoma). Theoretical calculations were performed by the group of Prof. Stanton (University of Florida). The THz measurements were performed at Wright State University in collaboration with Prof. Jason Deibel. This work has been supported by the National Science Foundation through grants Career Award DMR-0846834, AFOSR Young Investigator Program 06NE231. A portion of this work was performed at the National High Magnetic Field Laboratory (in collaboration with Dr. Stephen McGill), which is supported by National Science Foundation Cooperative Agreement No. DMR-0654118, the State of Florida, and the U.S. Department of Energy.
Ph. D.

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Jackson, Richard Simon. « Structural studies of PVC gels by Raman spectroscopy ». Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.344026.

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James, Christopher Dominic. « PARAMAGNETIC RESONANCE STUDIES OF HIGH-SPIN COBALT (II) COORDINATION COMPLEXES ». Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami152267342524459.

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Lovett, Brendon. « Three molecular materials studied by positive muons and magnetometry ». Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365360.

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Szilagyi, Petra Agota. « Study of iron-chelates in solid state and aqueous solutions using Mössbauer spectroscopy ». Toulouse 3, 2007. http://thesesups.ups-tlse.fr/142/.

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Ce travail a été consacré à l'étude du complexe éthylènediamine tétra-acétate de fer(III) (FeIIIEDTA) et de ses analogues : cyclohexanediamine tétra-acétate de fer(III) (FeIIICDTA) et (N,N')éthylènediamine di-acétate de fer(III) (FeIIIEDDA). Les structures de ces complexes en solutions aqueuses aux pH différents ont été proposées. La photodégradation du FeIIIEDTA ainsi que l'auto-oxydation du système Fe2+/EDTA dans les états solide et en solution ont été étudiées. Les mécanismes des réactions entre les complexes de FeIIIEDTA/CDTA/EDDA et l'H2O2 ainsi que la structure des intermédiaires issus de ces réactions ont été proposés. La relaxation magnétique du complexe NaFeEDTA. 3H2O à l'état solide ainsi que sa stabilité thermique et l'oxydation à l'air des produits issus de sa dégradation thermique (deux espèces de fer(II)) ont été étudiées par spectrométrie Mössbauer
This work has been devoted to the investigation of the ferric ethylenediaminetetraacetate, FeIIIEDTA and its analogues: the ferric cyclohexanediaminetetraacetate, FeIIICDTA and the ferric (N,N')ethylenediaminediacetate, FeIIIEDDA complexes. Structure of these complexes in aqueous solutions at different pH values have been proposed. The photodegradation of the FeIIIEDTA complex as well as the autoxidation of the Fe2+/EDTA system in solid state and in aqueous solution phase have been studied. Reaction pathways and structures for intermediate species forming in the course of the reaction between FeIIIEDTA/CDTA/EDDA and H2O2 have been proposed. The magnetic relaxation of the solid NaFeEDTA. 3H2O as well as the thermal stability and further aerial degradation of the decomposition products have been studied using Mössbauer spectroscopy

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Xie, Mouzhe. « Probing and Modeling Biomolecule-Nanoparticle Interactions by Solution Nuclear Magnetic Resonance Spectroscopy ». The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532049249287026.

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Ubben, Kai Ubbo. « Untersuchung der Spinrelaxation in GaN anhand spin- und zeitaufgelöster differentieller Reflektanzspektroskopie ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17134.

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Im Rahmen dieser Arbeit werden Untersuchungen der Spinrelaxation in epitaktischen GaN-Schichten mit unterschiedlichen Donatorkonzentrationen und Versetzungsdichten mit Hilfe spin- und zeitaufgelöster differentieller Reflektanzspektroskopie präsentiert. Dabei wurden die optischen Anregungsbedingungen sehr sorgfältig gewählt. Neben der genauen Abstimmung der Anregungsenergie, unterstützt durch die Modellierung der differentiellen Reflektanz, wurden insbesondere spektral schmale Laserpulse verwendet. Diese erlauben eine selektive Anregung der untersuchten Übergänge. Es wurden Spinlebensdauern von 30 bis 170~ps bei tiefen Temperaturen für das freie A-Exziton bestimmt. In der Nähe des Metall-Isolator-Übergangs ließ sich eine langsamere Spinrelaxation als für schwächer dotierte Proben nachweisen. Die längsten beobachteten Spinrelaxationszeiten zeigen freistehende GaN-Schichten hoher Materialqualität mit sehr geringen Versetzungsdichten. In der Literatur besteht eine kategorische Unterteilung der Ergebnisse in lange elektronische Spinlebensdauern bis in den Nanosekundenbereich, erhalten mit Kerr-Messungen, und extrem kurze exzitonische Spinrelaxation in Reflektanz-Experimenten im (Sub-)Pikosenkundenbereich. Dieses Bild wird hier nicht bestätigt. Die beobachteten Spinrelaxationszeiten liegen eineinhalb bis zweieinhalb Größenordnungen über Ergebnissen, von denen bisher mit der hier verwendeten Methode berichtet wurde. Es wird gezeigt, dass die Beobachtungen extrem kurzer Spinrelaxationszeiten an anderer Stelle eine Folge der optischen Anregungsbedingungen sind. Die Verwendung sehr kurzer und damit spektral breiter Laserpulse, die eine selektive Exziton-Anregung verbieten, führt zu einem deutlich anderen zeitlichen Verhalten und stark verfälschten Ergebnissen. Diese Beobachtung löst den scheinbaren Widerspruch zwischen den beiden Ergebnisgruppen in der Literatur auf und bildet die Grundlage für weiterführende Untersuchungen.
In this work, an investigation of spin relaxation in GaN epitaxial layers with different doping concentrations and dislocation densities is presented. The measurements were carried out by the means of spin- and time-resolved differential reflectance spectroscopy. The conditions of optical excitation were chosen with special care. In particular, spectrally narrow laser pulses were used to achieve selective excitation of the examined transitions in addition to the precise adjustment of the excitation energy, supported by the modeling of the differential reflectance. The spin relaxation times obtained for the free A exciton at low temperatures are in the range of 30 to 170 ps. In the proximity of the metal insulator transition, a slower spin relaxation was observed than for lower doping concentrations. The longest spin relaxation times were found in high quality, free-standing GaN layers with very low dislocation densities. Existing results in the literature can be strictly grouped into long electronic spin lifetimes of up to a few nanoseconds, obtained with Kerr rotation, and extremely short spin relaxation in the (sub)picosecond range, measured with reflectance experiments. This picture cannot be confirmed here. The spin relaxation times observed here lie 1.5 to 2.5 orders of magnitude above the values previously reported using the same experimental method. It is shown that the instances of extremely fast spin relaxation are caused by the properties of the optical excitation. The use of ultra-short and thus spectrally broad laser pulses, which prohibits the selective excitation of excitons, leads to a significantly different temporal behavior and strongly distorted results. This finding elucidates the apparent conflict between the two groups of results and forms the basis for further investigations.

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Lam, James. « Hydrogen diffusion in concentrated metal hydrides ». Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301906.

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Stelzl, Lukas Sebastian. « Studying marcomolecular transitions by NMR and computer simulations ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6e4bbe06-fc58-471b-a932-d940fe78b9a5.

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Macromolecular transitions such as conformational changes and protein-protein association underlie many biological processes. Conformational changes in the N-terminal domain of the transmembrane protein DsbD (nDsbD) were studied by NMR and molecular dynamics (MD) simulations. nDsbD supplies reductant to biosynthetic pathways in the oxidising periplasm of Gram-negative bacteria after receiving reductant from the C-terminal domain of DsbD (cDsbD). Reductant transfer in the DsbD pathway happens via protein-protein association and subsequent thiol-disulphide exchange reactions. The cap loop shields the active-site cysteines in nDsbD from non-cognate oxidation, but needs to open when nDsbD bind its interaction partners. The loop was rigid in MD simulations of reduced nDsbD. More complicated dynamics were observed for oxidised nDsbD, as the disulphide bond introduces frustration which led to loop opening in some trajectories. The simulations of oxidised and reduced nDsbD agreed well with previous NMR spin-relaxation and residual dipolar coupling measurements as well as chemical shift-based torsion angle predictions. NMR relaxation dispersion experiments revealed that the cap loop of oxidised nDsbD exchanges between a major and a minor conformation. The differences in their conformational dynamics may explain why oxidised nDsbD binds its physiological partner cDsbD much tighter than reduced nDsbD. The redox-state dependent interaction between cDsbD and nDsbD is thought to enhance turnover. NMR relaxation dispersion experiments gave insight into the kinetics of the redox-state dependent interaction. MD simulations identified dynamic encounter complexes in the association of nDsbD with cDsbD. The mechanism of the conformational changes in the transport cycle of LacY were also investigated. LacY switches between periplasmic open and cytoplasmic open conformations to transport sugars across the cell membrane. Two mechanisms have been proposed for the conformational change, a rocker-switch mechanism based on rigid body motions and an “airlock” like mechanism in which the transporter would switch conformation via a fully occluded structure. In MD simulations using the novel dynamics importance sampling approach such a fully occluded structure was found. The simulations argued against a strict “rocker-switch” mechanism.

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Brown, Richard Matthew. « Coherent transfer between electron and nuclear spin qubits and their decoherence properties ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:21e043b7-3b72-44d7-8095-74308a6827dd.

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Conventional computing faces a huge technical challenge as traditional transistors will soon reach their size limitations. This will halt progress in reaching faster processing speeds and to overcome this problem, require an entirely new approach. Quantum computing (QC) is a natural solution oﬀering a route to miniaturisation by, for example, storing information in electron or nuclear spin states, whilst harnessing the power of quantum physics to perform certain calculations exponentially faster than its classical counterpart. However, QCs face many diﬃculties, such as, protecting the quantum-bit (qubit) from the environment and its irreversible loss through the process of decoherence. Hybrid systems provide a route to harnessing the beneﬁts of multiple degrees of freedom through the coherent transfer of quantum information between them. In this thesis I show coherent qubit transfer between electron and nuclear spin states in a ¹⁵N@C₆₀ molecular system (comprising a nitrogen atom encapsulated in a carbon cage) and a solid state system, using phosphorous donors in silicon (Si:P). The propagation uses a series of resonant mi- crowave and radiofrequency pulses and is shown with a two-way ﬁdelity of around 90% for an arbitrary qubit state. The transfer allows quantum information to be held in the nuclear spin for up to 3 orders of magnitude longer than in the electron spin, producing a ¹⁵N@C₆₀ and Si:P ‘quantum memory’ of up to 130 ms and 1.75 s, respectively. I show electron and nuclear spin relaxation (T₁), in both systems, is dominated by a two-phonon process resonant with an excited state, with a constant electron/nuclear T₁ ratio. The thesis further investigates the decoherence and relaxation properties of metal atoms encapsulated in a carbon cage, termed metallofullerenes, discovering that exceptionally long electron spin decoherence times are possible, such that these can be considered a viable QC candidate.

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Lloyd, Sion. « The magnetic properties of superconductors ». Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343847.

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46

Iordanov, Iordan. « Structure and dynamics of the outer membrane protein A from Klebsiella pneumoniae : a joint NMR–SMFS–proteolysis and MS approach ». Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1602/.

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"KpOmpA est une protéine de la membrane externe de K. Pneumoniae. Elle fait partie de la famille des "outer membrane protein A", OmpA. KpOmpA est une protéine constituée de deux domaines: un domaine transmembranaire structuré en tonneau ß et une partie soluble, périplasmique. Le domaine transmembranaire de KpOmpA présente une homologie importante avec celle d'OmpA d'E. Coli dont la structure a été déterminée par cristallographie aux rayons X et spectroscopie RMN. OmpA d'E. Coli est responsable lors de la formation de biofilm. Elle a un rôle d'adhésine et d'invasine. Elle est la cible préférentielle du système immunitaire et est le récepteur de bactériophages. Il est admis que la plupart de ces fonctions sont dues aux boucles extracellulaires de ces protéines. Les différences majeures entre les protéines KpOmpA et OmpA d'E. Coli concernent les boucles extracellulaires de longueur plus importante dans le cas de KpOmpA. Elles jouent un rôle important au cours de l'activation des macrophages et des cellules dendritiques par la voie des récepteurs TLR2. Les boucles extracellulaires jouent un rôle essentiel au cours de l'activation du système immunitaire. Mieux définir la structure et la dynamique de ces boucles est d'une importance essentielle afin de mieux appréhender la fonctionnalité des boucles extracellulaires de KpOmpA. Les informations structurales connues actuellement (structure RMN déterminée dans le groupe IPBS RMN en 2009) ont été obtenus jusqu'à présent avec des échantillons de protéines recombinantes purifiées et repliées dans des micelles de détergent. Dans le présent travail, nous avons d'abord établi un protocole de reconstitution de la protéine dans une membrane phospholipidique et caractérisé nos échantillons par microscopie électronique. Des expériences de spectroscopie de force atomique sur molécule unique ont été réalisées pour caractériser le repliement de la protéine dans son environnement membranaire. Ces expériences suggèrent un nouveau rôle de KpOmpA au sein même de la membrane (collaboration D. Müller, ETH Zürich). Le domaine soluble périplasmique de la protéine a été exprimé indépendamment du domaine membranaire. Les premières expériences HSQC réalisées montrent une structuration de ce domaine. La structure de ce domaine par spectroscopie RMN est en cours de réalisation. Le comportement dynamique des boucles extracellulaires du domaine membranaire KpOmpA reconstitué dans des liposomes a été étudié par spectroscopie RMN à l'angle magique (MAS) et notamment par mesure des temps de relaxation. Nous avons montré que la dynamique intrinsèque de la protéine est indépendante de l'environnement (membrane vs micelle). Des expériences de protéolyse ménagée suivie par spectrométrie de masse (MALDI-TOF) ont été comparées avec les informations RMN afin d'évaluer plus précisément les niveaux de mobilité des différentes boucles extracellulaires. La préservation au cours de l'évolution des boucles extracellulaires semble lier à leur dynamique, ce qui suggère l'importance de ces boucles extracellulaires, en termes de séquence, longueur mais aussi de dynamique lors de la réponse immunitaire. "
KpOmpA is a two-domain membrane protein from Klebsiella pneumoniae belonging to the outer membrane protein A (OmpA) family. It is composed of a transmembrane ß-barrel with 8 ß-strands and a C-terminal, soluble periplasmic domain. The transmembrane domain presents a significant homology with E. Coli OmpA whose three dimensional structure has been determined by X-ray crystallography and by NMR. The E. Coli homologue can function as an adhesin and invasin, participate in biofilm formation, act as both an immune target and evasin, and serves as a receptor for several bacteriophages. It is assumed that most of these functions involve the four protein loops that emanate from the protein to the exterior of the cell. The difference between KpOmpA and E. Coli OmpA is mostly concentrated in these extracellular loops which are larger in the case of KpOmpA. KpOmpA was shown to activate macrophages and dendritic cells through the TLR2 dependent pathway, and these larger loops are supposed to play a specific role in the interactions with the immune system. Thus the structure and dynamics of these loops is of prime functional significance. The currently available information in this regard, including the NMR structure determined in the IPBS NMR group in 2009, have been obtained so far with recombinant protein samples purified and refolded in detergent micelles. In the present work we first established a reconstitution protocol that allowed the incorporation of the membrane protein in the more native environment of the lipid bilayer and characterised our samples by electron microscopy. SMFS experiments were used to probe the reconstituted KpOmpA unfolding-refolding pathways, exploring the folding mechanisms for ß-barrel proteins and suggesting a novel role for OmpA in the bacterial membrane (in collaboration with the group of D. Müller, ETH Zürich). The C-terminal periplasmic domain of KpOmpA was expressed and purified as a separate product and the feasibility of its structure elucidation by NMR was demonstrated by obtaining a high quality HSQC spectrum. The dynamic behaviour of the extracellular portion of the KpOmpA membrane domain reconstituted in liposomes has been investigated by solid state MAS NMR relaxation experiments. We confirmed that the previously observed gradient of dynamic along the molecule axis is an intrinsic property of the protein. Limited proteolysis and MALDI-TOF experiments were coupled with the NMR information in order to assess more precisely the different mobility levels in the loops. Evolutional preservation of the different loops regions is related to their observed flexibility, pointing towards immunologically important, variable, dynamic and accessible loops sections

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Silva, Marcos Antonio da. « Estudo de compostos LiMePO4 (Me=Mg, Co, Ni) através de Ressonância Magnética Nuclear ». Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-13032014-112117/.

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Nesta dissertação é apresentado um estudo dos compostos Li1-3xMgFexPO4 através de Ressonância Magnética Nuclear (7Li e 31P), no intervalo de temperatura de 150 a 410 K. Estudos desses compostos através de técnicas de difração de elétrons e efeito Mossbauer confirmam que os íons Fe entram na rede cristalina na forma Fe3+, substituindo os íons Li+. O comportamento dos espectros de RMN, dos tempos de relaxação spin-rede e da susceptibilidade magnética dos núcleos 7Li e 31P em função da temperatura, em conjunto com medidas de condutividade iônica, indicam que, mesmo com a adição de impurezas Fe3+ na rede, os íons Li+ pouca mobilidade dentro do intervalo de temperatura utilizado.
This work reports a 7Li and 31P nuclear magnetic resonance study in the Li1-3xMgFexPO4 phases between 150 and 410 K. This study, complementary to those made using Mössbauer and magnetic neutron diffraction experiments, confirms that the Fe3+ ions enter as in the lattice, and that they enter substituting Li ions. The behavior of the 7Li e 31P nuclear magnetic resonance spectra, together with ionic conductivity measurements, show that no Li mobility occurs in temperature range studied even with the addition of the Fe impurity.

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Tesi, Lorenzo. « Multitechnique investigation for rational design of molecular spin qubits ». Doctoral thesis, 2019. http://hdl.handle.net/2158/1150777.

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The investigation of the relaxation times of a series of vanadium(IV)-based molecular spin qubits in order to find a correlation to their structural properties. The magnetic system and the lattice structure have been studied by using a multitechnique investigation based on EPR, ac susceptometry, THz spectroscopy and 4D-Inelastic Neutron Scattering. New techniques have been proposed, such as Muon Spin Relaxation spectroscopy, and first preliminary results have been achieved by investigating Dy-based SMMs. A small part of the work is devoted to the characterization of a cobalt(II)-based SMM and 1D spin helices based on lanthanides by using Cantilever Torque Magnetometry.

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Kamusella, Sirko. « Electronic phase diagrams and competing ground states of complex iron pnictides and chalcogenides : A Mössbauer spectroscopy and muon spin rotation/relaxation study ». Doctoral thesis, 2016. https://tud.qucosa.de/id/qucosa%3A30237.

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In this thesis the superconducting and magnetic phases of LiOH(Fe,Co)(Se,S), CuFeAs/CuFeSb, and LaFeP_1-xAs_xO - belonging to the 11, 111 and 1111 structural classes of iron-based arsenides and chalcogenides - are investigated by means of 57Fe Mössbauer spectroscopy and muon spin rotation/relaxation (μSR). Of major importance in this study is the application of high magnetic fields in Mössbauer spectroscopy to distinguish and characterize ferro- (FM) and antiferromagnetic (AFM) order. A user-friendly Mössbauer data analysis program was developed to provide suitable model functions not only for high field spectra, but relaxation spectra or parameter distributions in general. In LaFeP_1-xAs_xO the reconstruction of the Fermi surface is described by the vanishing of the Γ hole pocket with decreasing x. The continuous change of the orbital character and the covalency of the d-electrons is shown by Mössbauer spectroscopy. A novel antiferromagnetic phase with small magnetic moments of ~ 0.1 μ_B state is characterized. The superconducting order parameter is proven to continuously change from a nodal to a fully gapped s-wave like Fermi surface in the superconducting regime as a function of x, partially investigated on (O,F) substituted samples. LiOHFeSe is one of the novel intercalated FeSe compounds, showing strongly increased T_C = 43 K mainly due to increased interlayer spacing and resulting two-dimensionality of the Fermi surface. The primary interest of the samples of this thesis is the simultaneously observed ferromagnetism and superconductivity. The local probe techniques prove that superconducting sample volume gets replaced by ferromagnetic volume. Ferromagnetism arises from magnetic order with T_C = 10 K of secondary iron in the interlayer. The tendency of this system to show (Li,Fe) disorder is preserved upon (Se,S) substitution. However, superconductivity gets suppressed. The results of Mössbauer spectroscopy indicate that the systems tends to a secondary structural phase, where the local iron environment observed in pure FeS is absent. Moreover, two interlayer positions of the iron are identified. The absence of enhanced superconducting T_C in LiOHFeS thus is related to a structural instability. Also, in CuFeAs the role of secondary iron at the Cu position turns out to be decisive for the observed magnetic behaviour. As in LiOHFeSe, it orders ferromagnetically at T_C ~ 11 K and superimposes with the magnetic instability of the main iron site. It is shown that a small charge doping of 0.1e/Fe, which is expected from (Cu,Fe) disorder, is sufficient to switch the system between a paramagnetic and an AFM ground state. Both magnetic orders are indistinguishable, because the magnetic order parameters are strongly coupled. This coupling was observed in the structurally identical CuFeSb, where the magnetic order parameters of both iron sites scale perfectly. The magnetically unstable CuFeAs and the ferromagnetic CuFeSb can be classified according to the theory of As height driven magnetism, predicting a change from paramagnetism to AFM and finally FM with increasing As height.:1 Acronyms and Symbols 2 Introduction 3 Iron-based arsenides and chalcogenides 3.1 Structural properties 3.2 Electronic properties 3.2.1 Magnetism 3.2.2 Superconductivity 3.2.3 Nematic phase 3.3 Investigated samples 4 Moessfit - a free Mössbauer fitting program 4.1 Aspects of program design 4.2 Errors 4.2.1 Uncorrelated 4.2.2 Hesse 4.2.3 MonteCarlo 4.2.4 Minos 4.3 Fitting algorithm 4.4 Maximum entropy method (MEM) 4.5 Kolmogorov-Smirnov confidence 5 Mössbauer spectroscopy 5.1 Mössbauer effect 5.2 Relativistic Doppler effect 5.3 Full static Hamiltonian 5.3.1 Quadrupole interaction 5.3.2 Isomer shift. 5.3.3 Zeeman splitting 5.3.4 Combined interaction 5.3.5 Transition probabilities 5.3.6 The magic angle 5.4 Transmission integral 5.4.1 Absorption area 5.4.2 Ideal thickness 5.4.3 Line width and line shape 5.4.4 Levelling 5.5 Applied field measurements of powder samples 5.5.1 Paramagnet, axial symmetric EFG in transverse field geometry 6 5.5.2 Uniaxial antiferromagnet, axial symmetric EFG in transverse field geometry 6 5.5.3 Paramagnet, axial symmetric EFG in longitudinal field geometry 6 5.5.4 Uniaxial ferromagnet, axial symmetric EFG in transverse field geometry 6 5.5.5 Polarised photons 5.5.6 Total absorption cross section 5.5.7 Polarised sources 5.6 Blume line shape model 6 μSR 6.1 Muon decay and detection 6.2 Magnetic order and dynamic relaxation 6.2.1 Magnetic order 6.2.2 Time dependent field distributions 6.2.3 Aspects of μSR in iron-based arsenides and chalcogenides 6.2.4 Weak transverse field (WTF) 6.3 Superconductivity - transverse field (TF) experiments 7 Intercalated FeSe 7.1 Bulk properties: XRD, susceptibility, resistivity 7.2 Structural characterization 7.3 LiOHFeSe - Mössbauer spectroscopy 7.3.1 Applied transverse field 7.4 LiOHFeSe - μSR 7.4.1 Zero field (ZF) 7.4.2 Pinning experiment 7.4.3 Transverse field (TF) 7.5 Mössbauer investigation of LiOHFe_1-yCo_ySe_1-xS_x. 7.6 Discussion 8 LaFeO(As,P) 8.1 Preliminary measurements and electronic structure calculations 8.2 Mössbauer spectroscopy 8.3 μSR 8.3.1 Magnetic characterization 8.3.2 Spin dynamics 8.3.3 Superconductivity 8.4 Discussion 9 CuFeAs and CuFeSb 9.1 Preliminary results of CuFeAs and CuFeSb 9.2 CuFeAs: Mössbauer spectroscopy 9.2.1 Zero field (ZF) 9.2.2 Longitudinal field (LF) 9.2.3 Transverse field (TF) 9.3 CuFeAs: μSR 9.3.1 Zero field (ZF) 9.3.2 Weak transverse field (WTF) 9.4 Further investigations on CuFeAs 9.4.1 Neutron scattering 9.4.2 Theoretical calculation 9.4.3 Local element analysis with EDX/WDX 9.5 CuFeSb: Mössbauer spectroscopy 9.5.1 Zero Field (ZF) 9.5.2 Transverse field (TF) 9.6 Discussion 10 Conclusion 11 Appendix 11.1 Derivation of the quadrupole interaction and isomer shift 11.2 Matrix form of the static nuclear Hamiltonian 11.3 Mössbauer line intensities 11.4 Blume line shape model 11.4.1 Special case: two states with diagonal Hamiltonians 11.5 Moessfit models 11.5.1 FeSe_1-xS_x(Li_1-zFe_zOH) ZF, standard 11.5.2 FeSe_1-xS_x(Li_1-zFe_zOH) ZF, 4 fractions 11.5.3 FeSe_1-xS_x(Li_1-zFe_zOH) Pinning 11.5.4 FeSe_1-xS_x(Li_1-zFe_zOH) TF 11.5.5 FeSe_1-xS_x(Li_1-zFe_zOH) CS-Vzz-MEM 11.5.6 LaFeP_1-xAs_x+ ferrocene, ZF 11.5.7 LaFeP_1-xAs_x+ ferrocene, LF 11.5.8 LaFeP_1-xAs_x+ iron foil, ZF 11.5.9 LaFeAsO ZF 11.5.10 LaFeAsO TF 11.5.11 CuFeAs + ferrocen, ZF 11.5.12 CuFeAs + ferrocen, ZF, high statistics 11.5.13 CuFeAs + ferrocen, LF 11.5.14 CuFeAs + ferrocen, TF 11.5.15 CuFeSb ZF 11.5.16 CuFeSb TF

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Goltz, Til. « On the electronic phase diagram of Ba1-xKx(Fe1-yCoy)2As2 and EuFe2(As1-xPx)2 superconductors : A local probe study using Mössbauer spectroscopy and Muon Spin Relaxation ». Doctoral thesis, 2015. https://tud.qucosa.de/id/qucosa%3A29145.

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In this thesis, I study the electronic and structural phase diagrams of the superconducting 122 iron pnictides systems Ba1-xKx(Fe1-yCoy)2As2 and EuFe2(As1-xPx)2 by means of the local probe techniques 57Fe Mössbauer spectroscopy (MS) and muon spin relaxation (muSR). For both isovalent substitution strategies - Co/K for Fe/Ba and P for As, respectively - the antiferromagnetic Fe ordering and orthorhombic distortion of the parent compounds BaFe2As2 and EuFe2As2 are subsequently suppressed with increasing chemical substitution and superconductivity arises, once long-range and coherent Fe magnetic order is sufficiently but not entirely suppressed. For Ba1-xKx(Fe1-yCoy)2As2 in the charge compensated state (x/2=y), a remarkably similar suppression of both, the orthorhombic distortion and Fe magnetic ordering, as a function of increasing substitution is observed and a linear relationship between the structural and the magnetic order parameter is found. Superconductivity is evidenced at intermediate substitution with a maximum Tsc of 15 K coexisting with static magnetic order on a microscopic length scale. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to nonmagnetic impurities to a system with a constant charge carrier density. Within this model, the experimental findings are compatible with the predicted s± pairing symmetry. For EuFe2(As1-xPx)2, the results from 57Fe MS and ZF-muSR reveal an intriguing interplay of the local Eu 2+ magnetic moments and the itinerant magnetic Fe moments due to the competing structures of the iron and europium magnetic subsystems. For the investigated single crystals with x=0.19 and 0.28, 57Fe MS evidences the interplay of Fe and Eu magnetism by the observation of a transferred hyperfine field below Tafm at which the Eu subsystem orders into a canted A-type AFM magnetic structure. Furthermore, an additional temperature dependent out-of-plane tilting of the static Fe hyperfine field is observed below the onset of static Eu ordering. ZF-muSR shows a strong increase of the local field at the muon site below Tafm=20 K and a crossover from isotropic to anisotropic Eu spin-dynamics between 30 and 10 K. The temperature dependence of the spin dynamics, as derived from the muSR dynamic relaxation rates, are related to a critical slowing down of Eu-spin fluctuations which extends to even much higher temperatures (~100 K). They also effect the experimental linewidth observed in the 57Fe MS experiments. The strong influence of the Eu magnetic order onto the primary observables in both methods prevents conclusive interpretation of the experimental data with respect to a putative interplay of Fe magnetism and superconductivity.

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