<p> The theoretical treatment of the induced torque problem is discussed, and equations describing the functional form of the torque amplitude are derived on the basis of a model calculation valid in the high field limit. This functional form is applied to a detailed interpretation of the open orbit structure in gallium, cadmium, zinc and copper. </p> <p> An investigation of the open orbit structure in gallium at l.4°K using this technique has yielded direct information on the connectivity of the sixth-band hole surface. This surface supports a k(c)-trajectory for all field directions in the ab plane, except within 0.1° of the a-axis. A k(a)-trajectory of lower conductivity is reported over a 10° range of field direction centred (32°±2°) from the b-axis in the be plane. These data, in addition to the highly anisotropic amplitude and field dependence of the k(c) -trajectory, require that this surface contact the Brillouin zone boundary at both the k(a) -and k(c) -faces. The present data are compared with available models of the sixth band hole surface, and are found to be in excellent agreement with the predictions of recent pseudopotential calculations . The possibility of magnetic breakdown in the k(c)-trajectory for B|| b-axis is discussed. Finally, a non-linear frequency dependence, and an anisotropic non-quadratic field dependence are understood to occur through the long mean free path and short skin depth parameters in gallium at l.4°K. </p> <p> In cadmium, the induced torque amplitude due to the [0001]-open trajectory tends to saturation at high field intensities for all observation directions. This effect is attributed to magnetic breakdown between the first-and secondhand hole surfaces through the spin·-orbit interaction energy 'gap near the H-symmetry point in the AHL plane. This magnetic breakdown effect is analyzed on the basis of a linear chain model and the theoretical curves of Falicov and Sievert. Detailed analysis indicates the possibility of two separate breakdown probabilities across the HL and HA gaps; for <1010> directions , breakdown fields of 10.8 k0e and (as low as) 0.72 k0e are indicated . A similar range of breakdown fields is indicated for all field directions in the (0001) plane. </p> <p> In zinc, the induced torque technique is used to investigate magnetic breakdown effects in the [0001]-trajectory for specific field directions in the basa l plane. These effects are attributed to the onset of partial breakdown between the monster and cap surfaces near the H-symrnetry points, for field intensities above 16 kOe. The linear chain model is shown to be an inappropriate description of breakdown effects in zinc. An onset field of 16 kOe for <1120> is determined; no breakdown is observed along <lOIO> below 20 kOe. In addition, magnetic breakdown effects occurring in the basal orbits of zinc were investigated. The general monotonic rise in torque amplitude with field intensities is fitted to the theoretical expressions of Falicov, Pippard, and Sievert. The giant quantum oscillations arising through coherence-effect modulation of the breakdown probability are shown consistent with earlier data. </p> <p> The technique is applied to a general survey of the various types of open orbits existing in copper, and the general applicability of the sample torque equations to both compensated and uncompensated metals is demonstrated. </p> / Thesis / Doctor of Philosophy (PhD)

In equine medicine, experience regarding MRI of chronic tendon lesions is limited, and evidence on the suitability of different sequences in 3 T high-field MRI is scarce. Therefore, macroscopically healthy and altered tendons were examined by histology and in 0.27 T low- and 3 T high-field MRI, focusing on T1-weighted (T1w) sequences to visualize chronic lesions. In high-field MRI, tendons were positioned parallel (horizontal) and perpendicular (vertical) to the magnetic field, acknowledging the possible impact of the magic angle effect. The images were evaluated qualitatively and signal intensities were measured for quantitative analysis. Qualitative evaluation was consistent with the quantitative results, yet there were differences in lesion detection between the sequences. The low-field T1w GRE sequence and high-field T1w FLASH sequence with vertically positioned tendons displayed all tendon lesions. However, the horizontally scanned high-field T1w SE sequence failed to detect chronic tendon lesions. The agreement regarding tendon signal intensities was higher between high-field sequences scanned in the same orientation (horizontal or vertical) than between the same types of sequence (SE or FLASH), demonstrating the impact of tendon positioning. Vertical scanning was superior for diagnosis of the tendon lesions, suggesting that the magic angle effect plays a major role in detecting chronic tendon disease.

This thesis focuses on improving the performance of the THz time-domain spectroscopy system using second-order nonlinear crystals for THz generation and detection in terms of bandwidth, sensitivity, and THz field strength. The theories for the THz generation based on optical rectification and detection technique, electro-optical sampling, based on Pockels effect are introduced in Chapter 2. In Chapter 3, some experiments are presented to characterize the performances of the THz system based on a 180 fs Yb:KGW femtosecond laser amplifier operating at 1035 nm. The Yb-based femtosecond laser is becoming increasingly popular due to its robustness, high repetition rate, and high average power. However, the NIR bandwidth of these femtosecond lasers is limited by the gain bandwidth of the gain medium, and achieving pulse durations shorter than 180 fs is challenging. Consequently, the full bandwidth of THz time-domain spectroscopy systems is constrained by such laser systems. In order to broaden the THz bandwidth of such THz time-domain spectroscopy systems, our work in Chapter 4 combines the Yb:KGW femtosecond laser amplifier with an argon-filled hollow-core photonic crystal fiber pulse shaper to spectrally broaden the near-infrared pulses from 3.5 to 8.7 THz, increasing the measured THz bandwidth correspondingly from 2.3 THz to 4.5 THz. This is one of the first works to have broadband THz system based on Yb-based femtosecond lasers in the year of 2018. In Chapter 5, the tilted-pulse-front phase matching in the THz generation and detection scheme is demonstrated using the same surface-etched phase gratings on the front surfaces of the 2 mm-thick GaP generation and detection crystals. This scheme overcomes the THz generation and detection bandwidth limit of thick crystals imposed by the traditional collinear phase matching, while allowing the long nonlinear interaction length. This results in a THz spectral range from 0.1 to 6.5 THz with a peak at 3 THz and a peak dynamic range of 90 dB. In the range between 1.1 and 4.3 THz, the system dynamic range exceeds 80 dB. Based on this contact grating-based THz generation, the next step involves generating high-field THz above 2 THz. For high-field THz generation, the most renowned technique is the tilted-pulse-front technique, which generates high-field THz below 2 THz in a LiNbO₃ crystal. Most nonlinear optics experiments in the THz regime rely on such THz sources. To generate high-field THz above 2 THz, one promising candidate is organic THz crystals. However, most organic crystals require a pump laser with a wavelength exceeding 1200 nm, necessitating a more complex laser system. Additionally, the low damage threshold of these crystals are susceptible to compromise the stability of the measurements. Other techniques, such as air plasma and metallic spintronics, can generate ultra-broadband high-field THz from 0.1 to 30 THz, but the pulse energy within certain frequency windows is relatively low, rendering these THz sources less effective for nonlinearly driving specific optical transitions. On the other hand, semiconductor crystals as THz generation crystals, have a high damage threshold and can achieve good phase matching at wavelength around 800 or 1000 nm. In Chapter 6, high-field THz generation with a peak field of 303 kV/cm and a spectral peak at 2.6 THz is achieved with a more homogenous grating on the surface of a 1 mm-thick GaP generation crystal in a configuration collimating the near-infrared generation beam with a pulse energy of 0.57 mJ onto the generation crystal. The experiments also show that the system operates significantly below the GaP damage threshold and THz generation saturation regime, indicating that the peak THz field strength can approach 1 MV/cm, with a 5 mJ near-infrared generation pulse. This is the first high-field THz source based on semiconductor crystals capable of generating high-field THz above 2 THz. With such a THz source, we can conduct nonlinear optics experiments above 2 THz, including the study of phonon-assisted nonlinearities, coherent control of Bose-Einstein condensation of excitons and polaritons in semiconductor cavities, and saturable absorption in molecular gases.

No description available.

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.

L’imagerie par résonance magnétique (IRM) est un outil d’investigation majeur donnant accès de manière non invasive à des nombreuses informations quantitatives et fonctionnelles. La qualité des images obtenues (rapport-signal-sur-bruit, RSB) est cependant limitée dans certaines applications nécessitant des résolutions spatiales et/ou temporelles poussées. Afin d’améliorer la sensibilité de détection des équipements d’IRM, diverses orientations peuvent être suivies telles qu’augmenter l’intensité du champ magnétique des imageurs, améliorer les performances des systèmes de détection radiofréquence (RF), ou encore développer des séquences d’acquisition et des techniques de reconstruction d’images plus efficaces. La thématique globale dans laquelle s’inscrit cette thèse concerne le développement des systèmes de détection RF à haute sensibilité pour l’IRM à haut champ chez l’homme. En particulier, des antennes auto-résonantes basées sur le principe des lignes de transmission sont utilisées parce qu’elles peuvent être réalisée sur substrat souple. Cette adaptabilité géométrique du résonateur permet d’ajuster précisément sa forme aux spécificités morphologiques de la zone anatomique observée, et ainsi d’augmenter le RSB. La première visée technologique de ce projet concerne le développement, de la conception jusqu’à la mise en œuvre dans un appareil 7 T corps entier, d’un système de détection RF flexible à haute sensibilité, utilisant des antennes miniatures associées en réseau. L’utilisation d’un réseau d’antennes miniatures permet d’obtenir des images sur un champ de vue élargi tout en conservant la haute sensibilité inhérente à chaque antenne miniature. De plus, la technologie de l’imagerie parallèle devient accessible, ce qui permet d’accélérer l’acquisition des images. De surcroît, un nouveau schéma de résonateur de ligne transmission avec un degré de liberté supplémentaire est introduit, ce qui permet de réaliser de grands résonateurs multi-tours pour l’IRM à haut champ. Cette thèse décrit le développement, la mise en œuvre et l’évaluation des nouveaux systèmes de détection RF au moyen de simulations analytiques et numériques, et des études expérimentales. / Magnetic resonance imaging (MRI), among other imaging techniques, has become a major backbone of modern medical diagnostics. MRI enables the non-invasive combined, identification of anatomical structures, functional and chemical properties, especially in soft tissues. Nonetheless, applications requiring very high spatial and/or temporal resolution are often limited by the available signal-to-noise ratio (SNR) in MR experiments. Since first clinical applications, image quality in MRI has been constantly improved by applying one or several of the following strategies: increasing the static magnetic field strength, improvement of the radiofrequency (RF) detection system, development of specialized acquisition sequences and optimization of image reconstruction techniques. This work is concerned with the development of highly sensitive RF detection systems for biomedical ultra-high field MRI. In particular, auto-resonant RF coils based on transmission line technology are investigated. These resonators may be fabricated on flexible substrate which enables form-fitting of the RF detector to the target anatomy, leading to a significant SNR gain. The main objective of this work is the development of a flexible RF coil array for high-resolution MRI on a human whole-body 7 T MR scanner. With coil arrays, the intrinsically high SNR of small surface coils may be exploited for an extended field of view. Further, parallel imaging techniques are accessible with RF array technology, allowing acceleration of the image acquisition. Secondly, in this PhD project a novel design for transmission line resonators is developed, that brings an additional degree of freedom in geometric design and enables the fabrication of large multi-turn resonators for high field MR applications. This thesis describes the development, successful implementation and evaluation of novel, mechanically flexible RF devices by analytical and 3D electromagnetic simulations, in bench measurements and in MRI experiments.

L'objectif de cette thèse repose sur le développement et la mise en œuvre des techniques de transmission parallèle (pTx) en Imagerie par Résonance Magnétique pour homogénéiser l’excitation des spins dans le cerveau humain à ultra-haut champ. Afin de permettre des démonstrations in-vivo, un concept de sécurité conservateur mais viable est introduit pour le contrôle de la puissance de la radiofréquence (RF) transmise. Par la suite, de nouvelles méthodes de minimisation du Taux d’Absorption Spécifique local et de conception d’impulsions RF non-sélectives sont investiguées. L’impact de ces impulsions courtes et relativement peu énergétiques, appelées « kT-points », est d'abord démontré dans l’approximation des petits angles de bascule de l’aimantation. Pour cibler un éventail d’applications plus large, la conception de type kT-points est ensuite généralisée en englobant les excitations à grand angle de bascule et les inversions. Cette méthode est appliquée à l'une des séquences pondérées en T1 les plus couramment utilisées en neuro-imagerie. Les résultats ainsi obtenus à 7 Tesla sont comparés à des images acquises avec une configuration clinique à 3 Tesla. Les principes de la méthode sont ainsi validés et démonstration est faite que la transmission parallèle permet aux systèmes à très haut champ d’être aussi compétitifs en imagerie pondérée en T1. Enfin, des simplifications dans la conception globale de la pTx sont étudiées pour un meilleur rapport coût-efficacité des solutions proposées. / The focus of this thesis lies on the development, and implementation, of parallel transmission (pTx) techniques in magnetic resonance imaging for flip-angle homogenization throughout the human brain at ultra-high field. In order to allow in-vivo demonstrations, a conservative yet viable safety concept is introduced to control the absorbed radiofrequency (RF) power . Subsequently, novel methods for local SAR control and non-selective RF pulse-design are investigated. The impact of these short and energy-efficient waveforms, referred to as kT-points, is first demonstrated in the context of the small-tip-angle domain. Targeting a larger scope of applications, the kT-points design is then generalized to encompass large flip angle excitations and inversions. This concept is applied to one of the most commonly used T1-weighted sequences in neuroimaging. Results thus obtained at 7 Tesla are compared to images acquired with a clinical setup at 3 Tesla, validating the principles of the kT-points method and demonstrating that pTx-enabled ultra-high field systems can also be competitive in the context of T1-weighted imaging. Finally, simplifications in the global design of the pTx-implementation are studied in order to obtain a more cost-effective solution.

Cette thèse présente le développement d’une méthodologie qui permet d’analyser la structure en couches du cortex cérébral, en utilisant l’imagerie par résonance magnétique en champ intense (IRM à 7 teslas). Alors que l’architecture corticale est traditionnellement étudiée par imagerie microscopique de coupes de tissu post-mortem, l’utilisation d’une technique non invasive telle que l’IRM permet d’envisager d’étudier la lamination corticale in vivo, et ainsi de dépasser les atlas architecturaux classiques comme celui de Brodmann.Deux approches ont été utilisées pour l’acquisition d’images à haute résolution. La première, développée pour l’imagerie in vivo, utilise une reconstruction super-résolue à partir de coupes épaisses acquises dans différentes géométries. La seconde, basée sur une séquence tridimensionnelle optimisée pour l’imagerie post-mortem, a permis l’acquisition d’images de pièces anatomiques.La contribution principale de cette thèse réside dans le développement d’un couple de méthodes permettant d’extraire automatiquement, en chaque point du cortex, un profil caractérisant son architecture en couches. Pour permettre l’extraction robuste de ces profils, un modèle original de l’influence de la courbure corticale a été développé et implémenté.Ces méthodes ont été testées et validées sur plusieurs pièces anatomiques. Ce travail permet d’envisager la caractérisation de l’architecture des aires corticales, voire leur délimitation automatique, en utilisant l’IRM en champ intense. / This thesis presents the development of a methodology for the analysis of the layered structure of the cerebral cortex, using high-field magnetic resonance imaging (7-tesla MRI). While cortical layers are traditionally studied using microscopic imaging of post-mortem tissue slices, the use a non-invasive technique such as MRI will enable in vivo studies, and thus allow new approaches beyond the use of classical architectural atlases such as Brodmann's.Two imaging methodologies have been used to acquire high-resolution images. First, a method based on super-resolution reconstruction from thick slices acquired in different geometries was developed for in vivo imaging. Second, a three-dimensional imaging sequence optimized for post-mortem tissue allowed imaging excised brain specimen.The main contribution of this thesis consists of a pair of methods that perform an automatic extraction of cortical profiles, which characterize the laminar architecture at any cortical location. In order to allow robust extraction of these profiles, an original model of the influence of cortical curvature was developed and implemented.These methods were tested and validated on multiple brain specimen. This work allows envisaging an automatic microarchitectural characterization of cortical areas, and even architectural parcellation, using high-field MRI.

Due to recent progress in theory and the growing number of physical realizations, low-dimensional quantum magnets continue to receive a considerable amount of attention. They serve as model systems for investigating numerous physical phenomena in spin systems with cooperative ground states, including the field-induced evolution of the ground-state properties and the corresponding rearrangement of their low-energy excitation spectra. This work is devoted to systematic studies of recently synthesized low-dimensional quantum spin systems by means of multi-frequency high-field electron spin resonance (ESR) investigations. In the spin- 1/2 chain compound (C6H9N2)CuCl3 [known as (6MAP)CuCl3] the striking incompatibility with a simple uniform S = 1/2 Heisenberg chain model employed previously is revealed. The observed ESR mode is explained in terms of a recently developed theory, revealing the important role of the alternation and next-nearest-neighbor interactions in this compound. The excitations spectrum in copper pyrimidine dinitrate [PM·Cu(NO3)2(H2O)2]n, an S = 1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interaction, is probed in magnetic fields up to 63 T. To study the high field behavior of the field-induced energy gap in this material, a multi-frequency pulsed-field ESR spectrometer is built. Pronounced changes in the frequency-field dependence of the magnetic excitations are observed in the vicinity of the saturation field, B ∼ Bs = 48.5 T. ESR results clearly indicate a transition from the soliton-breather to a spin-polarized state with magnons as elementary excitations. Experimental data are compared with results of density matrix renormalization group calculations; excellent agreement is found. ESR studies of the spin-ladder material (C5H12N)2CuBr4 (known as BPCB) completes the determination of the full spin Hamiltonian of this compound. ESR results provide a direct evidence for a pronounced anisotropy in this compound, that is in contrast to fully isotropic spin-ladder model employed previously for BPCB. Our observations can be of particular importance for describing the rich temperature-field phase diagram of this material. The frequency-field diagram of magnetic excitations in the quasi-two dimensional S = 1/2 compound [Cu(C4H4N2)2(HF2)]PF6 in the AFM-ordered state is studied. The AFM gap is observed directly. Using high-field magnetization and ESR results, parameters of the effective spin-Hamiltonian (exchange interaction, anisotropy and g-factor) are obtained and compared with those estimated from thermodynamic properties of this compound.

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