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The full 3-D vector magnetic field of a solar filament prior to eruption is presented. The filament was observed with the Facility Infrared Spectropolarimeter at the Dunn Solar Telescope in the chromospheric He i line at 10830 {\AA} on May 29 and 30, 2017. We inverted the spectropolarimetric observations with the HAnle and ZEeman Light (HAZEL) code to obtain the chromospheric magnetic field. A bimodal distribution of field strength was found in or near the filament. The average field strength was 24 Gauss, but prior to the eruption we find the 90th percentile of field strength was 435 Gauss for the observations on May 29. The field inclination was about 67 degree from the solar vertical. The field azimuth made an angle of about 47 to 65 degree to the spine axis. The results suggest an inverse configuration indicative of a flux rope topology. He i intensity threads were found to be co-aligned with the magnetic field direction. The filament had a sinistral configuration as expected for the southern hemisphere. The filament was stable on May 29, 2017 and started to rise during two observations on May 30, before erupting and causing a minor coronal mass ejection. There was no obvious change of the magnetic topology during the eruption process. Such information on the magnetic topology of erupting filaments could improve the prediction of the geoeffectiveness of solar storms.

Das Co2FeSi/GaAs-Hybridsystem wurde hinsichtlich seiner Eignung für Anwendungen in der Spintronik untersucht. Die Heusler-Legierung Co2FeSi ist ein aussichtsreicher Kandidat für derartige Anwendungen, weil der vollständig geordneten Kristallphase Halbmetallizität, d. h. eine Spinpolarisation von 100% an der Fermi-Energie, vorhergesagt wird. Zunächst wurde im Rahmen dieser Arbeit die elektrische Spininjektion und Spindetektion in lateralen Transportstrukturen in der sogenannten nicht-lokalen Konfiguration sowohl für die vollständig geordnete, als auch für eine teilweise ungeordnete Kristallphase mittels Spinventil- und Hanle-Messungen nachgewiesen. Die Abhängigkeiten der Spinsignale vom Strom und von der Temperatur konnten erklärt werden und eine Spininjektionsefizienz von 16 bzw. 9% wurde ermittelt. Für den praktischen Einsatz werden allerdings lokale Spinventile benötigt, deren Funktionsfähigkeit für beide kristallinen Ordnungen demonstriert wurde. Der Magnetowiderstand, der ein Maß für die Güte der lokalen Spinventile darstellt, beträgt 0.03% und liegt im Bereich des theoretisch zu erwartenden Wertes. Anhand des sogenannten Fert-Kriteriums konnten die Gründe für diesen niedrigen Wert aufgezeigt werden. Des Weiteren ließ ein Vergleich der lokalen und nicht-lokalen Spinsignale auf eine hohe Spinpolarisation des Co2FeSi schließen. Die Spinextraktion bietet neben der Spininjektion eine weitere Möglichkeit zur Erzeugung einer Spinakkumulation in einem Halbleiter. Die Stromabhängigkeiten von Spininjektion und Spinextraktion unterscheiden sich für beide kristallinen Phasen des Co2FeSi. Das stark unterschiedliche Verhalten konnte anhand des Einflusses der jeweiligen Bandstruktur auf die Spinerzeugung erklärt werden. Des Weiteren konnte aus dem Vergleich zwischen der Messungen und der theoretisch vorhergesagten Bandstruktur der halbmetallische Charakter der vollständig geordneten Kristallphase nachgewiesen werden. The Co2FeSi/GaAs hybrid system was investigated regarding its suitability for spintronic applications. The Heusler-compound Co2FeSi is a promissing canditate for these kind of applications due to the predicted half-metallicity, i. e. a 100% spin polarisation at the Fermi energy, for its fully ordered crystall phase. The electrical spin injection and detection was demonstrated in lateral tranpost structures in the so called non-local geometry for the fully ordered and for a partly disordered crystall phase by observing spin valve signatures and Hanle characteristics. The current and temperature dependence of the spin signals was explained and a respective spin injection efficiencies of 16 and 9% determined. For practical use one needs local spin valves, which where demonstrated for both crystalline phases. The magnetoresistance, a measure of the goodness of a local spin valve, was 0.03%, i. e. in the theoretically expected range. Making use of the so-called Fert criterion the reasons for this low value could be pointed out. Further the quotient of the local and non-local spin signals implied a high spin polarisation of the Co2FeSi. Spin extraction is another method to create a spin accumulation in a semiconductor. The current dependece of the spin injection and the spin extraction signals strongly depends on the degree of ordering in the Co2FeSi lattice. The different behavior is explanied by the crucial influence of the respective electronic band structure on the spin generation processes. Further, the comparison between the measured signals and the theoretically calculated electronic band structure hints towards the half-metalicity of the fully ordered crystall phase of Co2FeSi.

The ability to inject spin-polarized carriers into a semiconductor (SC) by electrical means and to convert a spin accumulation into an electrical signal is expected to bring new functionalities. It has been shown that the efficient injection of spin-polarized carriers from a ferromagnetic transition metal (FM) into a SC requires the addition and the fine tuning of a spin-conserving resistance at the FM/SC interface. We've carried out a systematic study about the spin accumulation as a function of the modification of the interfacial properties by probing several semiconductor materials such as GaAs and Ge contacted with tunnel insulator (I)/FM injectors like MgO/CoFeB, Al2O3/Co and Al2O3/NiFe. Three-terminal magnetoresistance (MR) measurements in Hanle and inverted Hanle configuration reveal the influence of a fluctuating magnetic field leading to spin's decoherence. This produces an artificial broadening of the Hanle signal that implies an under-estimation of the extracted spin life-time, as well as an appearing spin accumulation amplitude several orders of magnitude larger than expected. These effects can be interpreted through a sequential injection on localized electronic states close to the SC/I interface. Spatial confinement of these states can explain the high amplitude of the observed signal. Studies in function of voltage and temperature are supporting this mechanism. Magnetic simulations of the fluctuating field originated from stray fields due to interface roughness, or hyperfine field on localized states have been carried out and succeed to reproduce our results qualitatively., La possibilité d'injecter électriquement des porteurs polarisés en spin dans un semiconducteur (SC) et de convertir une accumulation de spin en un signal électrique ouvre la voie à de nouvelles fonctionnalités. Il a été montré que l'injection efficace de porteurs depuis un métal de transition ferromagnétique (FM) vers un SC requiert la présence d'une résistance optimisée conservant le spin à l'interface FM/SC. Nous avons mené une étude systématique de l'accumulation de spin par rapport à la modification des propriétés d'interface en sondant différents semiconducteurs tels que GaAs et Ge ainsi que des injecteurs isolant tunnel (I)/FM MgO/CoFeB, Al2O3/Co et Al2O3/NiFe. Nos mesures de magnétorésistance (MR) en géométrie 3 terminaux, en configuration Hanle ou Hanle inverse, ont révélé l'existence d'un champ magnétique fluctuant créant une dépolarisation du spin. Ceci provoque un élargissement artificiel du signal Hanle qui amène dans ce cas à sous-estimer la mesure du temps de vie de spin, ainsi qu'une amplitude d'accumulation de spin plusieurs ordres de grandeur plus forte que prédit théoriquement. Ces effets peuvent s'interpréter par une injection séquentielle sur des états localisés proches de l'interface I/SC. Le confinement spatial de ces états permet de comprendre la forte amplitude du signal observé. Les études en fonction de la tension et de la température viennent étayer ce mécanisme. Des simulations magnétiques d'un champ fluctuant lié au champ de fuite induit par la rugosité d'interface ou au champ hyperfin sur les états localisés ont été menées et permettent de reproduire qualitativement nos résultats.

The ability to inject spin-polarized carriers into a semiconductor (SC) by electrical means and to convert a spin accumulation into an electrical signal is expected to bring new functionalities. It has been shown that the efficient injection of spin-polarized carriers from a ferromagnetic transition metal (FM) into a SC requires the addition and the fine tuning of a spin-conserving resistance at the FM/SC interface. We've carried out a systematic study about the spin accumulation as a function of the modification of the interfacial properties by probing several semiconductor materials such as GaAs and Ge contacted with tunnel insulator (I)/FM injectors like MgO/CoFeB, Al2O3/Co and Al2O3/NiFe. Three-terminal magnetoresistance (MR) measurements in Hanle and inverted Hanle configuration reveal the influence of a fluctuating magnetic field leading to spin's decoherence. This produces an artificial broadening of the Hanle signal that implies an under-estimation of the extracted spin life-time, as well as an appearing spin accumulation amplitude several orders of magnitude larger than expected. These effects can be interpreted through a sequential injection on localized electronic states close to the SC/I interface. Spatial confinement of these states can explain the high amplitude of the observed signal. Studies in function of voltage and temperature are supporting this mechanism. Magnetic simulations of the fluctuating field originated from stray fields due to interface roughness, or hyperfine field on localized states have been carried out and succeed to reproduce our results qualitatively.; La possibilité d'injecter électriquement des porteurs polarisés en spin dans un semiconducteur (SC) et de convertir une accumulation de spin en un signal électrique ouvre la voie à de nouvelles fonctionnalités. Il a été montré que l'injection efficace de porteurs depuis un métal de transition ferromagnétique (FM) vers un SC requiert la présence d'une résistance optimisée conservant le spin à l'interface FM/SC. Nous avons mené une étude systématique de l'accumulation de spin par rapport à la modification des propriétés d'interface en sondant différents semiconducteurs tels que GaAs et Ge ainsi que des injecteurs isolant tunnel (I)/FM MgO/CoFeB, Al2O3/Co et Al2O3/NiFe. Nos mesures de magnétorésistance (MR) en géométrie 3 terminaux, en configuration Hanle ou Hanle inverse, ont révélé l'existence d'un champ magnétique fluctuant créant une dépolarisation du spin. Ceci provoque un élargissement artificiel du signal Hanle qui amène dans ce cas à sous-estimer la mesure du temps de vie de spin, ainsi qu'une amplitude d'accumulation de spin plusieurs ordres de grandeur plus forte que prédit théoriquement. Ces effets peuvent s'interpréter par une injection séquentielle sur des états localisés proches de l'interface I/SC. Le confinement spatial de ces états permet de comprendre la forte amplitude du signal observé. Les études en fonction de la tension et de la température viennent étayer ce mécanisme. Des simulations magnétiques d'un champ fluctuant lié au champ de fuite induit par la rugosité d'interface ou au champ hyperfin sur les états localisés ont été menées et permettent de reproduire qualitativement nos résultats.

We investigate theoretically dark resonance spectroscopy for a dilute atomic vapor confined in a thin (micro-metric) cell. We identify the physical parameters characterizing the spectra and study their influence. We focus on a Hanle-type situation, with an optical irradiation under normal incidence and resonant with the atomic transition. The dark resonance spectrum is predicted to combine broad wings with a sharp maximum at line-center, that can be singled out when detecting a derivative of the dark resonance spectrum. This narrow signal derivative, shown to broaden only sub-linearly with the cell length, is a signature of the contribution of atoms slow enough to fly between the cell windows in a time as long as the characteristic ground state optical pumping time. We suggest that this dark resonance spectroscopy in micro-metric thin cells could be a suitable tool for probing the effective velocity distribution in the thin cell arising from the atomic desorption processes, and notably to identify the limiting factors affecting desorption under a grazing incidence., 12 pages, 11 figures theoretical article

Context. Narrowband imaging spectropolarimetry is one of the most powerful tools available to infer information about the intensity and topology of the magnetic fields present in extended plasma structures in the solar atmosphere.Aims. We describe the instrumental set-up and the observing procedure that we have developed and optimized at the Istituto Ricerche Solari Locarno in order to perform imaging spectropolarimetry. A measurement that highlights the potential of the ensuing observations for magnetic field diagnostics in solar prominences is presented.Methods. Monochromatic images of solar prominences were obtained by combining a tunable narrowband filter, based on two Fabry-Perot etalons, with a Czerny-Turner spectrograph. Linear and circular polarization were measured at every pixel of the monochromatic image with the Zurich Imaging Polarimeter, ZIMPOL. A wavelength scan was performed across the profile of the considered spectral line. The HAZEL inversion code was applied to the observed Stokes profiles to infer a series of physical properties of the observed structure.Results. We carried out a spectropolarimetric observation of a prominence, consisting of a set of quasi-monochromatic images across the HeI D-3 line at 5876 angstrom in the four Stokes parameters. The map of observed Stokes profiles was inverted with HAZEL, finding magnetic fields with intensities between 15 and 30 G and directed along the spine of the prominence, which is in agreement with the results of previous works.