5 results
Search Results
Now showing 1 - 5 of 5
- ItemHall-plot of the phase diagram for Ba(Fe1−xCox)2As2(London : Nature Publishing Group, 2016) Iida, Kazumasa; Grinenko, Vadim; Kurth, Fritz; Ichinose, Ataru; Tsukada, Ichiro; Ahrens, Eike; Pukenas, Aurimas; Chekhonin, Paul; Skrotzki, Werner; Teresiak, Angelika; Hühne, Ruben; Aswartham, Saicharan; Wurmehl, Sabine; Erbe, Manuela; Hänisch, Jens; Holzapfel, Bernhard; Drechsler, Stefan-Ludwig; Efremov, Dmitri V.The Hall effect is a powerful tool for investigating carrier type and density. For single-band materials, the Hall coefficient is traditionally expressed simply by , where e is the charge of the carrier, and n is the concentration. However, it is well known that in the critical region near a quantum phase transition, as it was demonstrated for cuprates and heavy fermions, the Hall coefficient exhibits strong temperature and doping dependencies, which can not be described by such a simple expression, and the interpretation of the Hall coefficient for Fe-based superconductors is also problematic. Here, we investigate thin films of Ba(Fe1−xCox)2As2 with compressive and tensile in-plane strain in a wide range of Co doping. Such in-plane strain changes the band structure of the compounds, resulting in various shifts of the whole phase diagram as a function of Co doping. We show that the resultant phase diagrams for different strain states can be mapped onto a single phase diagram with the Hall number. This universal plot is attributed to the critical fluctuations in multiband systems near the antiferromagnetic transition, which may suggest a direct link between magnetic and superconducting properties in the BaFe2As2 system.
- ItemPurely antiferromagnetic magnetoelectric random access memory(London : Nature Publishing Group, 2017) Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, DenysMagnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics.
- ItemInterface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films(London : Nature Publishing Group, 2015) Molatta, Sebastian; Haindl, Silvia; Trommler, Sascha; Schulze, Michael; Wurmehl, Sabine; Hühne, RubenThin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications.
- ItemLarge pinning forces and matching effects in YBa2Cu3O7-δ thin films with Ba2Y(Nb/Ta)O6 nano-precipitates(London : Nature Publishing Group, 2016) Opherden, Lars; Sieger, Max; Pahlke, Patrick; Hühne, Ruben; Schultz, Ludwig; Meledin, Alexander; Van Tendeloo, Gustaaf; Nast, Rainer; Holzapfel, Bernhard; Bianchetti, Marco; MacManus-Driscoll, Judith L.; Hänisch, JensThe addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.
- ItemHigh field superconducting properties of Ba(Fe1-xCox)2As2 thin films(London : Nature Publishing Group, 2015) Hänisch, Jens; Iida, Kazumasa; Kurth, Fritz; Reich, Elke; Tarantini, Chiara; Jaroszynski, Jan; Förster, Tobias; Fuchs, Günther; Hühne, Ruben; Grinenko, Vadim; Schultz, Ludwig; Holzapfel, BernhardThe film investigated grew phase-pure and highly textured with in-plane and out-of-plane full width at half maximum, FWHM, of = 0.74° and = 0.9°, Suppl. S1. The sample, however, does contain a large density of ab-planar defects, as revealed by transition electron microscope (TEM) images of focused ion beam (FIB) cuts near the microbridges, Fig. 1. These defects are presumably stacking faults (i.e. missing FeAs layers)20. The reason for this defect formation (also observed on technical substrates)21 is not fully understood. Possible reasons are a partial As loss during deposition22, and relaxation processes in combination with the Fe buffer layer23. Estimating the distance between these intergrowths leads to values varying between 5 and 10 nm. Between the planar defects, an orientation contrast is visible in TEM (inset Fig. 1b), i.e. the brighter crystallites are slightly rotated either around (010) (out-of-plane spread, ) or around (001) (in-plane spread, ) and enclosed by dislocation networks or small-angle GBs. Since the crystallites are sandwiched between planar defects, an in-plane misorientation is most likely. The out-of-plane misorientation, on the other hand, is visible as a slight tilt of the ab-planar defects with respect to each other, especially in the upper part of the sample. No globular or columnar precipitates were found.