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- ItemThree-Dimensional Imaging of Magnetic Domains with Neutron Grating Interferometry(Amsterdam [u.a.] : Elsevier, 2015) Manke, I.; Kardjilov, N.; Schäfer, R.; Hilger, A.; Grothausmann, R.; Strobl, M.; Dawson, M.; Grünzweig, Ch.; Tötzke, Ch.; David, Ch.; Kupsch, A.; Lange, A.; Hentschel, M.P.; Banhart, J.This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique.
- ItemMultistate current-induced magnetization switching in Au/Fe/MgO(001) epitaxial heterostructures(College Park, MD : APS, 2021) Gospodarič, P.; Młyńczak, E.; Soldatov, I.; Kákay, A.; Bürgler, D.E.; Plucinski, L.; Schäfer, R.; Fassbender, J.; Schneider, C.M.Magnetization switching using in-plane charge current recently has been widely investigated in heavy metal/ferromagnet bilayers with the switching mechanism usually attributed to the action of the spin-orbit coupling. Here we study in-plane current induced magnetization switching in model epitaxial bilayers that consist of Au(001) and Fe(001) grown on MgO(001). We use the planar Hall effect combined with magnetooptical Kerr effect (MOKE) microscopy to investigate magnetic properties of the bilayers and current-induced switching. We show that a current density beyond 1.4×107 A/cm can be employed for reproducible electrical switching of the magnetization between multiple stable states that correspond to different arrangements of magnetic domains with magnetization direction along one of the in-plane easy magnetization axes of the Fe(001) film. Lower current densities result in stable intermediate transversal resistances which are interpreted based on MOKE-microscopy investigations as resulting from the current-induced magnetic domain structure that is formed in the area of the Hall cross. We find that the physical mechanism of the current-induced magnetization switching of the Au/Fe/MgO(001) system at room temperature can be fully explained by the Oersted field, which is generated by the charge current flowing mostly through the Au layer.
- ItemTime-reversal symmetry breaking type-II Weyl state in YbMnBi2(London : Nature Publishing Group, 2019) Borisenko, S.; Evtushinsky, D.; Gibson, Q.; Yaresko, A.; Koepernik, K.; Kim, T.; Ali, M.; van den Brink, J.; Hoesch, M.; Fedorov, A.; Haubold, E.; Kushnirenko, Y.; Soldatov, I.; Schäfer, R.; Cava, R.J.Spectroscopic detection of Dirac and Weyl fermions in real materials is vital for both, promising applications and fundamental bridge between high-energy and condensed-matter physics. While the presence of Dirac and noncentrosymmetric Weyl fermions is well established in many materials, the magnetic Weyl semimetals still escape direct experimental detection. In order to find a time-reversal symmetry breaking Weyl state we design two materials and present here experimental and theoretical evidence of realization of such a state in one of them, YbMnBi2. We model the time-reversal symmetry breaking observed by magnetization and magneto-optical microscopy measurements by canted antiferromagnetism and find a number of Weyl points. Using angle-resolved photoemission, we directly observe two pairs of Weyl points connected by the Fermi arcs. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties.
- ItemThe magneto-optical gradient effect in an exchange-biased thin film: Experimental evidence for classical diffraction theory(Milton Park : Taylor & Francis, 2010) Schäfer, R.; Hamann, C.; McCord, J.; Schultz, L.; Kamberský, V.The magneto-optical gradient effect decorates the boundaries of in-plane domains even at perpendicular incidence of light in an optical polarization microscope. For its explanation, the classical magneto-optical diffraction theory was previously used to derive the effect from the same gyrotropic interaction as the Kerr effect. In order to explain the symmetry of the experimentally observed contrast on bulk ferromagnetic crystals, planar as well as perpendicular subsurface gradients in the magnetization had to be assumed. This was particularly needed when the surface magnetizations in neighboring domains pointed head-on and a gradient contrast appeared also in conditions of vanishing gyrotropic interaction at the surface. The gradient contrast in such conditions should not appear in very thin films where perpendicular magnetization gradients are not enforced by reduction of magnetostatic energy. Here we present the first experimental confirmation of this expectation, thus closing an experimental gap in verifying the predictions of the diffraction theory.
- ItemDomain evolution during the spin-reorientation transition in epitaxial NdCo5 thin films(Milton Park : Taylor & Francis, 2013) Seifert, M.; Schultz, L.; Schäfer, R.; Neu, V.; Hankemeier, S.; Rössler, S.; Frömter, R.; Oepen, H.P.The domain structure and its changes with temperature were investigated for an epitaxial NdCo5 thin film with in-plane texture in which a spin-reorientation transition takes place from the easy c-axis via the easy cone to the easy plane. Scanning electron microscopy with polarization analysis reveals a transition from a two-domain state at temperatures above 318 K via a four-domain state back to a 90°-rotated two-domain state at temperatures below 252 K. The transition temperatures correspond well to those determined by global magnetization measurements. The magnetization configuration at the three different regimes of magnetic anisotropy and its transition with temperature were analysed in detail. From the local measurements, the spin-reorientation angle and the magnetocrystalline anisotropy constants of first and second order were derived.
- ItemThe Filter Imager SuFI and the Image Stabilization and Light Distribution System ISLiD of the Sunrise Balloon-Borne Observatory: Instrument Description(Dordrecht [u.a.] : Springer Science + Business Media, 2011) Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T.L.; Solanki, S.K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.; Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger, J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch, G.; Knölker, M.; Martínez Pillet, V.; Bonet, J.A.; Schmidt, W.; Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.; Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.We describe the design of the Sunrise Filter Imager (SuFI) and the Image Stabilization and Light Distribution (ISLiD) unit onboard the Sunrise balloon borne solar observatory. This contribution provides the necessary information which is relevant to understand the instruments' working principles, the relevant technical data, and the necessary information about calibration issues directly related to the science data. © 2010 The Author(s).
- ItemDynamic volume magnetic domain wall imaging in grain oriented electrical steel at power frequencies with accumulative high-frame rate neutron dark-field imaging(London : Nature Publishing Group, 2018) Harti, R.P.; Strobl, M.; Schäfer, R.; Kardjilov, N.; Tremsin, A.S.; Grünzweig, C.The mobility of magnetic domains forms the link between the basic physical properties of a magnetic material and its global characteristics such as permeability and saturation field. Most commonly, surface domain structure are studied using magneto-optical Kerr microscopy. The limited information depth of approx. 20 nanometers, however, allows only for an indirect interpretation of the internal volume domain structures. Here we show how accumulative high-frame rate dynamic neutron dark-field imaging is able for the first time to visualize the dynamic of the volume magnetic domain structures in grain oriented electrical steel laminations at power frequencies. In particular we studied the volume domain structures with a spatial resolution of ∼100 μm and successfully quantified domain sizes, wall velocities, domain annihilation and its duration and domain wall multiplication in real time recordings at power frequencies of 10, 25 and 50 Hz with ±262.5 A/m and ±525 A/m (peak to peak) applied field.