5 results
Search Results
Now showing 1 - 5 of 5
- ItemDetermination of Bulk Magnetic Volume Properties by Neutron Dark-Field Imaging(Amsterdam [u.a.] : Elsevier, 2015) Grünzweig, Christian; Siebert, René; Betz, Benedikt; Rauscher, Peter; Schäfer, Rudolf; Lehmann, EberhardFor the production of high-class electrical steel grades a deeper understanding of the magnetic domain interaction with induced mechanical stresses is strongly required. This holds for non-oriented (NO) as well as grain-oriented (GO) steels. In the case of non-oriented steels the magnetic property degeneration after punching or laser cutting is essential for selecting correct obstructing material grades and designing efficient electrical machines. Until now these effects stay undiscovered due to the lack of adequate investigation methods that reveal local bulk information on processed laminations. Here we show how the use of a non-destructive testing method based on a neutron grating interferometry providing the dark-field image contrast delivers spatially-resolved transmission information about the local bulk domain arrangement and domain wall density. With the help of this technique it is possible to visualize magnetization processes within the NO laminations. Different representative manufacturing techniques are compared in terms of magnetic flux density deterioration such as punching, mechanically cutting by guillotine as well as laser fusion cutting using industrial high power laser beam sources. For GO steel laminations the method is applicable on the one hand to visualize the internal domain structure without being hindered by the coating layer. On the other hand, we can show the influence of the coating layer onto the underlying domain structure.
- ItemMagnetooptical response of permalloy multilayer structures on different substrate in the IR-VIS-UV spectral range(Bristol : IOP Publ., 2019) Patra, Rajkumar; Mattheis, Roland; Stöcker, Hartmut; Monecke, Manuel; Salvan, Georgeta; Schäfer, Rudolf; Schmidt, Oliver G.; Schmidt, HeidemarieThe magnetooptical (MO) response of Ru/Py/Ta thin film stacks with 4, 8, and 17 nm thick Ni81Fe19 permalloy (Py) films on a SiO2/Si and a ZnO substrate was measured by vector magnetooptical generalized ellipsometry. The MO response from VMOGE was modelled using a 4 × 4 Mueller matrix algorithm. The wavelength-dependent, substrate-independent and thickness-independent complex MO coupling constant (Q) of Py in the Ru/Py/Ta thin film stacks was extracted by fitting Mueller matrix difference spectra in the spectral range from 300 nm to 1000 nm. Although the composition-dependent saturation magnetization of NixFe1−x alloys (x = 0.0...1.0), e.g. of Ni81Fe19, is predictable from the two saturation magnetization end points, the MO coupling constant of NixFe1−x is not predictable from the two Q end points. However, in a small alloy range (0.0 < x < 0.2 and 0.8 < x < 1.0) the composition-dependent Q of NixFe1−x can be interpolated from a sufficiently high number of analyzed NixFe1−x alloys. The available complex MO coupling constants of six different NixFe1−x (x = 1.0 to 0.0) alloys were used to interpolate MO response of binary NixFe1−x alloys in the range from x = 0.0 to x = 1.0.
- ItemAnalyzer-free, intensity-based, wide-field magneto-optical microscopy(Melville, NY : American Inst. of Physics, 2021) Schäfer, Rudolf; Oppeneer, Peter M.; Ognev, Alexey; Samardak, Alexander; Soldatov, Ivan V.In conventional Kerr and Faraday microscopy, the sample is illuminated with plane-polarized light, and a magnetic domain contrast is generated by an analyzer making use of the Kerr or Faraday rotation. Here, we demonstrate possibilities of analyzer-free magneto-optical microscopy based on magnetization-dependent intensity modulations of the light. (i) The transverse Kerr effect can be applied for in-plane magnetized material, as demonstrated for an FeSi sheet. (ii) Illuminating that sample with circularly polarized light leads to a domain contrast with a different symmetry from the conventional Kerr contrast. (iii) Circular polarization can also be used for perpendicularly magnetized material, as demonstrated for garnet and ultrathin CoFeB films. (iv) Plane-polarized light at a specific angle can be employed for both in-plane and perpendicular media. (v) Perpendicular light incidence leads to a domain contrast on in-plane materials that is quadratic in the magnetization and to a domain boundary contrast. (vi) Domain contrast can even be obtained without a polarizer. In cases (ii) and (iii), the contrast is generated by magnetic circular dichroism (i.e., differential absorption of left- and right-circularly polarized light induced by magnetization components along the direction of light propagation), while magnetic linear dichroism (differential absorption of linearly polarized light induced by magnetization components transverse to propagation) is responsible for the contrast in case (v). The domain-boundary contrast is due to the magneto-optical gradient effect. A domain-boundary contrast can also arise by interference of phase-shifted magneto-optical amplitudes. An explanation of these contrast phenomena is provided in terms of Maxwell-Fresnel theory. © 2021 Author(s).
- ItemMicromagnetic investigation of domain and domain wall evolution through the spin-reorientation transition of an epitaxial NdCo5 film([London] : IOP, 2017-3-1) Seifert, Marietta; Schultz, Ludwig; Schäfer, Rudolf; Hankemeier, Sebastian; Frömter, Robert; Oepen, Hans Peter; Neu, VolkerThe domain pattern and the domain wall microstructure throughout the spin-reorientation transition of an epitaxial NdCo5 thin film are investigated by micromagnetic simulations. The temperature-dependent anisotropy constants K1 and K2, which define the anisotropy energy term in the model, are chosen to reflect the easy axis—easy cone—easy plane spin-reorientation transition observed in epitaxial NdCo5 thin films. Starting at the high-temperature easy c-axis regime, the anisotropy constants are changed systematically corresponding to a lowering of the temperature of the system. The character of the domain walls and their profiles are analysed. The calculated domain configurations are compared to the experimentally observed temperature-dependent domain structure of an in-plane textured NdCo5 thin film.
- ItemDomain wall asymmetries in Ni81Fe19/NiO: Proof of variable anisotropics in exchange bias systems(Milton Park : Taylor & Francis, 2009) McCord, Jeffrey; Schäfer, RudolfMultiple changes in the internal structure of magnetic domain walls due to alterations of the interfacial coupling across the ferromagnetic/antiferromagnetic interface are reported for Ni81Fe19/NiO exchange coupled films. Depending on the antiferromagnetically induced anisotropy, three different types of domain walls are observed. Cross-tie domain wall structures of decreased vortex to anti-vortex spacing develop with the addition of a thin antiferromagnetic layer. For exchange biased samples strong asymmetries in domain wall structure occur for the ascending and descending branch of the magnetization loop. For the descending branch a symmetric 180° Néel wall develops, whereas a folded cross-tie domain wall structure forms during magnetization reversal along the ascending loop branch. The novel type of 'zig-zagged' cross-tie wall is characterized by cross-ties reaching differently into the surrounding domain areas. The wall alterations indicate the existence of bi-modal coupling strengths in exchange coupled systems, which is in accordance with models of exchange bias that assume pinned and unpinned spins at the ferromagnetic/antiferromagnetic interface.