Light-induced magnetization reversal of high-anisotropy TbCo alloy films

Magnetization reversal using circularly polarized light provides a new way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3x106 ergs/cm3. Optical magnetization switching is observed only for alloys which compensation temperature can be reached through sample heating

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Lange Zeit hat sich der Mensch damit begnügt, unseren Planeten, die Erde, zu entdecken, zu besiedeln und all seine Geheimnisse zu lüften. Auch wenn wir damit noch lange nicht fertig sind, strecken wir doch seit Jahren unsere Fühler immer weiter aus - bis in den Weltraum. Diese Welt, fernab von unserer, fasziniert den Menschen seit jeher. Doch was, wenn aus Faszination irgendwann Notwendigkeit wird? Was, wenn die Erde für den Menschen und seine Entwicklung nicht mehr ausreicht? In Sachen Ressourcen und der Erhaltung unserer Umwelt stoßen wir immer wieder auf Grenzen. So ist es nur natürlich, das der Mensch weiter vorausschaut. Was kann uns das Weltall mit all seinen Weiten in Zukunft bieten? Vermeintlich unentdeckte Welten warten nur darauf, uns ihre Möglichkeiten zu offenbaren

Zirkulierende Tumorzellen - voll automatisierte Vereinzelung aus Blut

Circulating tumor cells (CTCs) are interesting for both, cancer diagnostics and therapy. Hence for practical use, very efficient methods are required to enrich, detect and isolate the typically very low number of CTCs. Herein, we present the “CTCelect device”, enabling the fully automated counting and isolation of CTCs from a blood sample for further biological investigations

Equilibrium transport velocity of deformable cells and rigid sheres in micro-channels under laminar flow conditions

Inertial migration of particles to a characteristic lateral equilibrium position in laminar micro-flows has been investigated under various aspects during the last decades. The majority of the studies deal with the equilibrium position of rigid particles and viscous droplets. Here, we compare the equilibrium velocity of viscoelastic cells and rigid polystyrene spheres in flow by applying the method of spatially modulated emission. The technique allows the precise determination of the equilibrium velocity of an object in flow, which has been found to depend on object characteristics like size in earlier studies. Here, we first show that the deformable cells move at higher equilibrium velocity than rigid polystyrene particles, thus revealing that a particle’s equilibrium velocity is related to its deformability—in addition to size. In a second set of experiments, we treat cells with the cytostatic agent colchicine, which results in a systematic decrease of the equilibrium velocity that is attributed to cell stiffening. This study thus provides evidence that the parameter cell deformability can be extracted from the equilibrium velocity based on spatially modulated emission, which opens up an alternative way for high-throughput cell-deformability characterization

Selective solvent evaporation from binary mixtures of water and tetrahydrofuran using a falling film microreactor

In this work, a falling film micro reactor was investigated regarding its ability to continuously eliminate tetrahydrofuran (THF) out of a THF-water mixture via nitrogen stripping. Mass transfer measurements were performed at different temperatures and flow rates. The residual content of THF in the eluate was quantified with high precision (<0.1%) via density measurements. Remarkably, complete elimination of THF could be achieved for liquid volume flow rates smaller than 2 ml/min and nitrogen volume flow rates larger than 400 ml/min at all three investigated temperatures (55°C, 60°C, and 65°C). In order to assist future design processes of such binary microstripping systems, we further developed a mass transfer model for this separation process extending an existing model for evaporation of a pure liquid. The good agreement of experimental data and calculations in the overall investigated parameter range (≤20%, for gas flow rates below 500 ml/min ≤11%) shows the potential of the model for the prediction of alternative operational parameter settings, e.g. at different THF entrance concentrations

Subpicosecond magnetization dynamics in TbCo alloys

Équipe 101 : Nanomagnétisme et électronique de spinInternational audienceSince the discovery of all-optical magnetization switching in rare-earth transition-metal alloys the underlying magnetization dynamics of multisublattice magnets has become a hot topic of modern magnetism. We studied the ultrafast magnetization dynamics in TbCo alloys as a function of the alloy composition and the laser fluence using either 800 nm or 400 nm probe pulses. Direct comparison between TbCo samples with different compositions for equal excitation conditions demonstrates that the magnetization dynamics of the Co sublattice strongly depends on the Tb concentration. For Tb32Co68 the magnetization of the sublattices can even transiently be reversed on a subpicosecond time scale

Kerr and Faraday microscope for space- and time-resolved studies

Équipe 101 : Nanomagnétisme et électronique de spinInternational audienceWe present a multi-purpose scanning magneto-optical microscope for the investigation of magnetic thin films. The setup can be used for both static and time-resolved (pump-probe) measurements. It is moreover compatible with samples with arbitrary magnetic anisotropy, as it allows Kerr measurements in polar and longitudinal geometry as well as in transmission (Faraday geometry). We demonstrate that the microscope can be used in the following modi: (i) static imaging mode (in polar Kerr and Faraday geometry) with a spatial resolution of 1.7 mu m; (ii) time-resolved mode (polar Kerr geometry) with a temporal resolution of 300 femtoseconds

Energy-resolved magnetic domain imaging in TbCo alloys by valence band photoemission magnetic circular dichroism

Equipe 101 : Nanomagnétisme et électronique de spinInternational audienceWe report magnetic domain imaging of a terbium cobalt (TbCo) alloy thin film with a high perpendicular magnetic anisotropy in one- and two-photon photoemission electron microscopy (PEEM). Both photoemission processes deliver a clear magnetic circular dichroism (MCD) whose strength is strongly energy dependent. Comparing the energy dependence of the MCD signal in one- and two-photon photoemission, we conclude that the magnetic contrast is mainly an initial state effect. Our results ultimately show that MCD contrast can be obtained in PEEM in valence band photoemission from a material supporting all-optical magnetization switching. This opens the way for the investigation of the all-optical switching process with simultaneous ultrahigh temporal and spatial resolution