Anomalous Spontaneous Reversal in Magnetic Heterostructures

We observe a thermally induced spontaneous magnetization reversal of epitaxial ferromagnet/antiferromagnet heterostructures under a constant applied magnetic field. Unlike any other magnetic system, the magnetization spontaneously reverses, aligning anti-parallel to an applied field with decreasing temperature. We show that this unusual phenomenon is caused by the interfacial antiferromagnetic coupling overcoming the Zeeman energy of the ferromagnet. A significant temperature hysteresis exists, whose height and width can be tuned by the field applied during thermal cycling. The hysteresis originates from the intrinsic magnetic anisotropy in the system. The observation of this phenomenon leads to open questions in the general understanding of magnetic heterostructures. Moreover, this shows that in general heterogeneous nanostructured materials may exhibit unexpected phenomena absent in the bulk.Comment: 14 pages, 4 figure

The PIOLab: Building global physical input-output tables in a virtual laboratory

Informed environmental-economic policy decisions require a solid understanding of the economy’s biophysical basis. Global physical input-output tables ( gPIOTs) collate a vast array ofinformation on the world economy’s physical structure and its interdependence with the environment. However, building gPIOTs requires dealing with mismatched and incompleteprimary data with high uncertainties, which makes it a time-consuming and labor-intensive endeavor. We address this challenge by introducing the PIOLab: A virtual laboratory for building gPIOTs. It represents the newest branch of the Industrial Ecology virtual laboratory (IELab) concept, a cloud-computing platform and collaborative research environment through which participants can use each other’s resources to assemble individual input-output tables targeting specific research questions. To overcome the lack of primary data, the PIOLab builds extensively upon secondary data derived from a variety of models commonly used in Industrial Ecology. We use the case of global iron-steel supply chains to describe the architecture of the PIOLab and highlight its analytical capabilities. A major strength of the gPIOT is its ability to provide mass-balanced indicators on both apparent/direct and embodied/indirect flows, for regions and disaggregated economic sectors. We present the first gPIOTs for 10 years (2008-2017), covering32 regions, 30 processes and 39 types of iron/steel flows. Diagnostic tests of the data reconciliation show a good level of adherence between raw data and the values realized in the gPIOT. We conclude with elaborating on how the PIOLab will be extended to cover other materials and energyflows.Series: Ecological Economic Paper

Dissertatio Iuridica Inauguralis De Bonis Paraphernalibus

Quam Deo Optimo Maximo Praeside Ex Decreto & Authoritate ... ICtorum Collegii In ... Argentoratensium Academia ... Publicae & solenni censurae submittit Joh. Hippolytus Eisenmenger Heidelbergensis. Ad diem Maii ..

Reversible laser patterning of YBa2Cu3O7-delta microbridges

Thin films of YBa2Cu3O7-delta on MgO have been patterned using a laser writing technique based on the temperature increase in the focus of a laser beam. The corresponding local increase of the oxygen diffusion velocity can be employed to write reversibly deoxygenated (semiconducting) and reoxygenated (superconducting) patterns, if nitrogen or oxygen, respectively, is chosen as ambient atmosphere. The fully planar microbridges produced in this way have been characterized by electronic transport measurements, scanning probe microscopy and magnetooptics. The processed material exhibits the same superconducting properties as the virgin films

Microbridge on YBa2Cu307-delta thin film patterned by reversible laser annealing

A superconducting microbridge (14 μm wide, 140 μm long) on an epitaxial YBa2Cu3O7-d thin film was patterned by using a laser writing technique. The technique is based on a local increase of oxygen diffusion velocicity caused by the heat of a focussed laser beam. Using nitrogen as the ambient atmosphere a deoxygenated (semiconducting) line could be written. A reoxygenated (superconducting)line forming a microbridge could be patterned by scanning the laser beam in ambient oxygen atmosphere perpendicular to the first written line. Neither optical reflection micrographs nor scanninz electron microscopy images have shown any physical damage of the film surface due to this fully planar patterning technique. The reversible properties of the laser writing technique were proved by electrica1 four-point DC measurements between 30 K and 300 K

Influence of microscopic defects in type-II superconducting thin films on the magnetic flux penetration

The magnetic flux penetration into thin type-II superconducting films with circular defects is investigated. The artificial circular defects (diameter = 40 μm) in an YBa2Cu3O72d thin film (thickness = 300 μm) were prepared by pulse-laser irradiation. The flux penetration into the zero-field-cooled superconducting film was visualized by means of the magneto-optic method. A stepwise increase of the external magnetic field allowed a detailed investigation of the influence of local defects on the flux penetration. For a magnetic field parallel to a long sample (longitudinal geometry) with a long cylindrical defect a single parabolic discontinuity line appears. Also in the case of a thin superconducting film exposed to a transverse magnetic field (transverse geometry), a single parabolic discontinuity line has been supposed in the vicinity of a local defect. On the contrary, our investigations show that the flux and current distribution around a single defect in a superconducting thin film can be determined not by a single, but by two discontinuity parabolas. In thin superconducting films in transverse geometry screening currents in the Meissner region (j front

Ultrafast Magneto-Optical Study of Flux Avalanches in High-Tc Superconductors

An ultrafast magneto-optic pump-probe technique has been used to trigger and image a flux instability in high-temperature superconducting thin films. Snapshots of the dendritic flux avalanche spreading into the film could be obtained with a time resolution in the picosecond range

Magnetic instability in YBa2Cu307-delta films

Using a magneto-optic technique we have investigated the magnetic flux propagation into and out of superconducting thin YBa2Cu3O7-b films. After field cooling below Tc, the external magnetic field Bext perpendicular to the film is changed which gives rise to shielding currents in the sample. The current distribution is disturbed momentarily by heating with a focused laser pulse near the sample edge. This triggers a magnetic instability, in which a magnetic flux avalance starts to propagate

Magneto-Optic Characterization of Defects and Study of Flux Avalanches in High-Tc Superconductors down to Nanosecond Time Resolution

Optical methods offer an intrinsic high potential for experiments with excellent spatial and in particular also temporal resolution. Using the Faraday effect we carried out magneto-optical investigations of high-Tc superconductor thin films in a polarization microscope. Small defects in the superconducting material which possess a lower critical current density disturb the homogeneous penetration of magnetic flux into a sample when an external magnetic field is applied after zero field cooling. This is true even if the defects are below the sample surface or when the superconducting sample is covered by a thin layer of another material, e.g., gold, and can be used to characterize samples with diameters up to 3". For studies of the dynamics of magnetic flux in a superconducting sample, a pump-probe setup has been used. An instability which causes magnetic flux to enter the sample in dendritic form [1] is triggered by local heating with a focused ns or fs laser pulse. Part of the beam is separated by a beam splitter, passed through a variable delay line of suitable length and used for illumination of the sample. ForYBa2Cu307- 6 thin films a spreading velocity of (5 + 2) x 1o4 m/s is found which is an order of magnitude higher than the velocity of sound. The total area of the dendritic structure formed is found to depend linearly on the change Bext of the external magnetic flux density applied before the trigger pulse. No dependence on the pulse duration has been observed, suggesting a purely thermal nature of the trigger process