In this thesis, the interplay between electron transport and magnetization dynamics is explored in order to access to fundamental properties of ferromag- netic metal thin films. With the aim of extracting the influence of the electron surface scattering on the spin-dependent resistivities, thickness series of permal-loy (Ni80Fe20) films were grown and studied. In addition to standard electrical and magnetic measurements, a detailed study of the propagation of spin waves along these films was performed. Resorting to the current-induced spin-wave Doppler shift technique, the degree of spin-polarization of the electrical current was extracted. This degree of spin-polarization was found to decrease when the film thickness decreases, which suggests that the film surfaces contribute to the spin dependent resistivities and tend to depolarize the electrical current.

Two of the principal phenomena observed and exploited in the field of spintronics are giant magnetoresistance (GMR) and spin transfer torque (STT). With GMR, the resistance of a magnetic multilayer is affected by the relative orientation of its magnetic layers due to (electron) spin dependent scattering. For the STT effect, a spin-polarized electric current is used to alter the magnetic state of a ferromagnet. Together, GMR and STT are at the foundation of numerous technologies, and they hold promise for many more applications. To achieve the high current densities (~10¹² A/m²) that are necessary to observe STT effects, point contacts – constricted electrical pathways (~1–100 nm in diameter) between conducting materials – are often used because of their small cross-sectional areas. In this sense, we have explored STT in bilayer magnetic nanopillars, where an electric current was used to induce precession of a ferromagnetic layer. This precessional state was detected as an increase in resistance of the device, akin to GMR. Temperature dependent measurements of the onset of precession shed light on the activation mechanism, but raised further questions about its detailed theory. Point contacts can also be used as local sources or detectors of electrons. In this context, we have observed transverse electron focusing (TEF) in a single crystal of bismuth. TEF is a k-selective technique for studying electron scattering from within materials. Using lithographically fabricated point contacts, we have studied the temperature dependence of the relaxation time for ballistic electrons from 4.2 to 100 K. These measurements indicated a transition between electron-electron dominated scattering at low temperatures and electron-phonon scattering as the Debye temperature was approached. We present preliminary work toward a TEF experiment to measure spin dependent scattering from a non-magnet/magnet interface. We also investigated spin wave propagation in thin, magnetic waveguide structures. At the boundary between the waveguide and continuous magnetic film, spin wave rays were found to radiate into the film, or to reflect and form standing waves in the waveguide. A circular defect in the waveguide was observed to cause diffraction of spin waves, generating an interference pattern of higher modes of oscillation. / text

In dieser Arbeit werden Resultate elektronischer Transportmessungen von supraleitenden Eisenpniktiden und ferromagnetischen Heusler-Verbindungen diskutiert. Die Eisenpniktide sind eine neuartige Klassen von Hochtemperatursupraleitern, deren Eigenschaften sich aus einem Zusammenspiel von Supraleitung und Magnetismus ergeben. Während die sogenannten 122-Pniktide Antiferromagnetismus aufweisen und unter Dotierung in einen supraleitenden Zustand übergehen, konnte in dotiertem LiFeAs Ferromagnetismus beobachtet werden. Undotiert hingegen zeigt dieses Material interessante supraleitende Eigenschaften. Die Heusler-Verbindungen sind u.a. durch ihren Ferromagnetismus bekannt. Das hier untersuchte Co2FeSi ist einer der stärksten Ferromagnete. Der in diesem Material vorhergesagte vollständig spinpolarisierte elektronische Transport, d.h. alle Leitungselektronen besitzen den gleichen Spin, konnte nachgewiesen werden. Die hier genannten Eigenschaften können exzellent mit der Methode der elektronischen Transportmessungen untersucht werden. Deren Ergebnisse aus Messungen an Einkristallen werden in dieser Arbeit diskutiert. / In this work, results of electronic transport measurements are discussed for superconducting iron pnictides as well as for ferromagnetic Heusler compounds. The iron pnictides are a recently discovered class of high temperature superconductors where magnetism might play a crucial role. While the 122-pnictides show antiferromagnetism and migrate to the superconducting state upon doping, ferromagnetism has been observed in doped LiFeAs. On the other hand, in the undoped state this material shows interesting superconducting properties. Among other propierties, Heusler compounds are well known due to their ferromagnetism. Co2FeSi, which was investigated in this work, is one of the strongest ferromagnets. Beside this, one predicts this compound to be a half-metallic ferromagnet with completely spin polarized electronic transport where all conducting electrons have the same spin. The here addressed properties can well be investigated with the method of electronic transport measurements, whose results on single crystals are discussed in this work.

Dans cette thèse, nous proposons d’explorer la relation entre transport électronique et dynamique d’aimantation afin de mieux comprendre certaines propriétés des films minces de métaux ferromagnétiques. Afin d’extraire l’influencede la diffusion des électrons par les surfaces sur les résistivités dépendantes du spin, des séries d’épaisseur de films de permalloy (Ni80Fe20) ont été déposées et étudiées. En plus de mesures électriques et magnétiques conventionnelles,nous avons réalisé une étude détaillée de la propagation des ondes de spin dans ces films. La technique du décalage Doppler d’ondes de spin induit par un courant électrique a été utilisée pour extraire le degré de polarisation en spin du courant électrique. Nous avons observé que ce degré de polarisation décroît lorsque l’épaisseur du film décroît, ce qui suggère que les surfaces contribuent aux résistivités dépendantes du spin et qu’elles ont tendance à dépolariser le courant électrique. / In this thesis, the interplay between electron transport and magnetization dynamics is explored in order to access to fundamental properties of ferromag- netic metal thin films. With the aim of extracting the influence of the electron surface scattering on the spin-dependent resistivities, thickness series of permal-loy (Ni80Fe20) films were grown and studied. In addition to standard electrical and magnetic measurements, a detailed study of the propagation of spin waves along these films was performed. Resorting to the current-induced spin-wave Doppler shift technique, the degree of spin-polarization of the electrical current was extracted. This degree of spin-polarization was found to decrease when the film thickness decreases, which suggests that the film surfaces contribute to the spin dependent resistivities and tend to depolarize the electrical current.

In dieser Arbeit werden Resultate elektronischer Transportmessungen von supraleitenden Eisenpniktiden und ferromagnetischen Heusler-Verbindungen diskutiert. Die Eisenpniktide sind eine neuartige Klassen von Hochtemperatursupraleitern, deren Eigenschaften sich aus einem Zusammenspiel von Supraleitung und Magnetismus ergeben. Während die sogenannten 122-Pniktide Antiferromagnetismus aufweisen und unter Dotierung in einen supraleitenden Zustand übergehen, konnte in dotiertem LiFeAs Ferromagnetismus beobachtet werden. Undotiert hingegen zeigt dieses Material interessante supraleitende Eigenschaften. Die Heusler-Verbindungen sind u.a. durch ihren Ferromagnetismus bekannt. Das hier untersuchte Co2FeSi ist einer der stärksten Ferromagnete. Der in diesem Material vorhergesagte vollständig spinpolarisierte elektronische Transport, d.h. alle Leitungselektronen besitzen den gleichen Spin, konnte nachgewiesen werden. Die hier genannten Eigenschaften können exzellent mit der Methode der elektronischen Transportmessungen untersucht werden. Deren Ergebnisse aus Messungen an Einkristallen werden in dieser Arbeit diskutiert. / In this work, results of electronic transport measurements are discussed for superconducting iron pnictides as well as for ferromagnetic Heusler compounds. The iron pnictides are a recently discovered class of high temperature superconductors where magnetism might play a crucial role. While the 122-pnictides show antiferromagnetism and migrate to the superconducting state upon doping, ferromagnetism has been observed in doped LiFeAs. On the other hand, in the undoped state this material shows interesting superconducting properties. Among other propierties, Heusler compounds are well known due to their ferromagnetism. Co2FeSi, which was investigated in this work, is one of the strongest ferromagnets. Beside this, one predicts this compound to be a half-metallic ferromagnet with completely spin polarized electronic transport where all conducting electrons have the same spin. The here addressed properties can well be investigated with the method of electronic transport measurements, whose results on single crystals are discussed in this work.

Die Alzheimer Krankheit ist die häufigste Altersdemenz. Ein spezifisches pathologisches Merkmal der Alzheimer Krankheit ist die Amyloid-Ablagerung im Gehirn. Die Hauptkomponente der so genannten Amyloid-Plaques ist das Amyloid beta-Peptid (A-beta). A-beta entsteht durch sequenzielle proteolytische Spaltung aus einem membrangebundenen Vorläuferprotein, dem beta-APP (betaamyloid precursor protein). Die kürzlich identifizierte beta-Sekretase (BACE, beta-site APPcleaving enzyme) generiert den Schnitt am N-Terminus von A-beta. Es entsteht ein C-terminales, membrangebundenes beta-APP-Fragment, das beta-APP-CTF. Beta-APP-CTF ist das direkte Substrat für die gamma-Sekretase, die innerhalb der Membrandomäne schneidet, wodurch A-beta freigesetzt wird. In der vorliegenden Arbeit kann erstmalig gezeigt werden, dass BACE auf dem sekretorischen Transportweg aus dem Endoplasmatischen Retikulum (ER), über den Golgi-Apparat zur Zelloberfläche transportiert wird. Auf dem Transport wird BACE durch N-Glycosylierung und Propeptidabspaltung posttranslational modifiziert. BACE wird im ER N-glycosyliert und die mannosereichen Zucker werden auf dem Transport durch den Golgi-Apparat in Endoglycosidase H resistente Zucker des komplexen Typs modifiziert. Die Propeptidabspaltung, durch Furin oder furinähnliche Propeptidkonvertasen, findet unmittelbar vor dem Aufbau der komplexen Zucker statt. Ferner konnte gezeigt werden, dass der Transport von BACE die A-beta-Entstehung limitieren kann. In polarisierten Madin-Darby canine kidney (MDCK) Zellen wird BACE überwiegend zur apikalen Plasmamembran transportiert und damit entgegengesetzt zu seinem Substrat beta-APP. Der gegensätzliche Transport von BACE und beta-APP begrenzt die A-beta Entstehung. Wird der apikale Transport von beta-APP durch Deletion seines basolateralen Sortierungssignals erhöht, entsteht vermehrt A-beta. Der differenzielle Transport von BACE und beta-APP könnte ein Hinweis darauf sein, dass beta-APP nicht das physiologische Substrat von BACE ist. / Alzheimer`s disease is the most common cause of progressive cognitive decline in the aged population. Pathologically Alzheimer`s disease is characterized by the invariant accumulation of senile plaques. Senile plaques are predominantly composed of the amyloid beta-peptide (A-beta), which is derived from the membrane bound beta-amyloid precursor protein (beta-APP) by sequential proteolytic cleavage. The recently identified beta-secretase (BACE) is responsible for the cleavage at the N-terminus of the A-beta domain. This cleavage generates membrane-bound beta-APP-Cterminal fragments (beta-APP-CTF) which are the immediate precursor for gamma-secretase cleavage and therefore for liberation of A-beta. The present work shows that BACE moves along the secretory pathway, while it undergoes post-translational modifications, which can be monitored by a significant increase in the molecular mass and cleavage of its pro-peptide. BACE becomes N-glycosylated within the ER and the increase in molecular mass is caused by complex N-glycosylation. The mature form of BACE is resistant to endoglycosidase H treatment; this indicates that BACE traffics through the Golgi. Furthermore the mature form of BACE does not contain the pro-peptide anymore. Pro-BACE is predominantly located within the endoplasmic reticulum. Pro-peptide cleavage occurs immediately before full maturation by furin or a furin-like proprotein convertase. Moreover traffic of BACE can limit A-beta generation. In the well established model system of polarized Madin-Darby canine kidney (MDCK) cells, the majority of BACE is sorted to the apical domain. Interestingly it has been shown previously that the substrate of BACE, beta-APP is transported to the basolateral surface of MCDK cells. Therefore, substantial amounts of BACE are targeted away from beta-APP to a non-amyloidogenic compartment, a cellular mechanism that limits A-beta generation. Upon deletion of the basolateral sorting signal of beta-APP, apically missorted beta-APP is processed by BACE. The differential targeting of BACE and its substrate beta-APP suggest that beta-APP might not be the major physiological substrate of BACE.

Des mesures d’ondes de spin propagatives ont été réalisées pour caractériser deux effets de l’interaction spin-orbite ainsi que le transport électrique dépendant du spin. Les effets du couplage spin-orbite ont été étudiés dans des bicouches nickel-fer/platine. Dans ces films, les fréquences de deux ondes de spin contre-propageantes ne sont pas les mêmes, ce qui est attribué à l’effet combiné d’une interaction magnétique chirale appelée interaction Dzyaloshinskii-Moriya et d’une asymétrie dans l’épaisseur du film magnétique. En appliquant le courant électrique dans ce système nous avons observé une modification du taux de relaxation de l’onde de spin qui est attribuée au transfert de spin induit par effet Hall de spin. D’autre part, les études de propagation d’ondes de spin dans une couche mince de fer épitaxié à température ambiante ont montré une polarisation en spin du courant électrique de 83%, ce qui est attribué à une forte asymétrie du couplage électron-phonon. / Propagating spin wave measurements were realised to characterize two spin-orbit related phenomena, as well as spin dependent electrical transport. The effects of spin-orbit coupling have been studied in nickel-iron/platinum bilayers. It has been shown that in these films the frequencies of two counter-propagating spin waves are not the same, which is attributed to the combined effects of a chiral magnetic interaction named Dzyaloshinskii-Moriya interaction and an asymmetry of the magnetic properties across the film thickness. By applying an electrical current in such system we have observed a modification of the spin wave relaxation rate due to the spin transfer torque induced by spin Hall effect. On the other hand, from the study of spin wave propagation in thin epitaxial iron films at room temperature, a degree of spin polarization of the electrical current of 83% was extracted, which is attributed to a significant spin-asymmetry of the electron-phonon coupling.

In this work the electronic and magnetic structure of the crystals Sr2FeMoO6, Fe0.5Cu0.5Cr2S4, LuFe2O4 and the molecules FeStar, Mo72Fe30, W72Fe30 are investigated by means of X-ray spectroscopic techniques. These advanced materials exhibit very interesting properties like magnetoresistance or multiferroic behaviour. In case of the molecules they also could be used as spin model systems. A long standing issue concerning the investigation of these materials are contradicting results found for the magnetic and electronic state of the iron (Fe) ions present in these compounds. Therefore this work focuses on the Fe state of these materials in order to elucidate reasons for these problems. Thereby the experimental results are compared to multiplet simulations.