Physik: DPG Tagungen - Sitzung O 28 - Nano-science.de

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Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html Transverse magneto-optical Kerr effect at the 3p edges of Fe and Co •Armin Kleibert 1 , Sergio Valencia 2 , Hans-Christoph Mertins 2 und Joachim Bansmann 1 1 Universität Rostock, Fachbereich Physik, Universitätsplatz 3, 18051 Rostock 2 BESSY GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany Soft x-ray based experimental techniques are powerful and very sensitive methods to investigate the magnetism of systems with low dimensions like ultrathin films or clusters, respectively. In particular, the magneto-optical Kerr-effect (MOKE) at the 2p edges of Fe, Co, and Ni has attracted much attention. In the transverse geometry (T-MOKE) huge intensity changes in the resonantly enhanced reflectivity upon reversal of the magnetization direction have been found. While effects near the 2p core levels were extensively studied in the last years, only a few experiments were reported concerning the vicinity of the 3p threshold. In this contribution, we present angular dependent measurements of the T-MOKE in the energy range of the 3p edges of thin Fe and Co films, respectively, revealing surprisingly large asymmetries up to 40% near the Brewster angle. From these reflectivity measurements it is possible to obtain information about the energy dependent refractive indices and magneto-optical Voigt constants. In order to simulate the measured reflectivity including the influence of capping layers we applied a multilayer formalism describing magneto-optics. A good agreement of calculation and experiment was achieved using tabulated values of the index of refraction and independently obtained Voigt constants. O 28.83 Poster Mi 16:00 Bereich C Resonant X-Ray scattering from TbBaCo 2 O 5.5 •N.V. Kasper 1 , P. Wochner 1 , G. Carbone 1 , A. Vigliante 2 , D. Mannix 3 und G. Jakob 4 4 Institut für Physik, Universität Mainz, Mainz, Germany 1 Max-Planck-Institut für Metallforschung, Stuttgart, Germany 2 Bruker AXS, Karlsruhe, Germany 3 European Synchrotron Radiation Facility, Grenoble, France Resonant X-ray scattering at the Co K-edge from epitaxial films and single crystals of TbBaCo 2 O 5.5 cobaltite with perovskite structure has been studied in insulating and metallic states. Polarization, energy and azimuthal dependences of the intensity of (016), (116), and (310) Bragg peaks were measured. Strong oscillations of the resonantly scattered intensity were observed both in σ' and π' channels. The scattered signal changes very weakly during the metal-insulator phase transition. The azimuthal oscillations of the scattered signal are attributed to the tensor character of the anomalous scattering factor of Co. Using this concept we have developed a model, describing very well the measured azimuthal oscillations. On the basis of the obtained experimental results and literature data it is argued that this anisotropy of the anomalous scattering factor of Co is caused mainly by distortions of the local surrounding of cobalt ions and not by anisotropies due to ordering of electronic orbitals of Co. O 28.84 Poster Mi 16:00 Bereich C X-ray magneto-optical sum rules in small Co clusters •Kai Fauth 1,2 , Markus Heßler 1,2 und Gisela Schütz 2 1 Physikalisches Institut der Universität Würzburg, Am Hubland, 97074 Würzburg 2 MPI für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart The so-called spin and orbital sum rules [1,2] in x-ray magnetic circular dichroism (XMCD) spectroscopy are often believed to apply with reasonable accuracy in the case of the late 3d transition metals and their compounds, if the magnetic dipole term T z can be neglected. Strong deviations can occur due to symmetry breaking such as given at surfaces, causing the magnetic dipole term to contribute significantly to the spin sum 30 of 32 07.06.2009 22:14
Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html rule, while not contributing to the magnetization. Much less is known in the case of small clusters. We have derived magnetic moments of superparamagnetic Co 55 clusters from XMCD at various applied magnetic fields. We find that the moments thus obtained from the magnetization curve and those determined separately from the sum rules agree to within 10%. This result sets an upper limit for the importance of T z in these clusters. [1] B. T. Thole et al. , Phys. Rev. Lett. 68, 1943 (1992) [2] P. Carra et al. , Phys. Rev. Lett. 70, 694 (1993) O 28.85 Poster Mi 16:00 Bereich C X-ray resonant magnetic scattering of Fe/Cr superlattices •Alexei Nefedov, Johannes Grabis, Andre Bergmann, Florin Radu und Hartmut Zabel Institut für Experimentalphysik/Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany We have studied the magnetic and structural properties of an antiferromagnetically (AF) coupled Fe/Cr(001) superlattice by soft X-ray resonant magnetic scattering. Strong magnetic Bragg peaks are observed at the half order positions in reciprocal space parallel to the [001] growth direction and in between the structural Bragg reflections from the superlattice periodicity. The magnetic hysteresis loops measured at the structural Bragg peak and at the half-order peak clearly demonstrate the AF coupling of the Fe/Cr multilayer. Transverse scans and off-specular reflectivity measurements confirm an AF domain structure of the superlattice in remanence with large perpendicular correlation. In addition, the transverse scan of the half-order Bragg peak exhibits a Lorentzian line shape at zero field, which diminishes in higher fields, indicative for a remanent multidomain state which approaches a single domain state towards saturation. This work was supported by the German Federal Ministry of Education and Research (BMBF) under Contract No.03ZAE7BO. O 28.86 Poster Mi 16:00 Bereich C Inducing spin crossover in metallo-supramolecular polyelectrolytes through an amphiphilic phase transition •Yves Bodenthin 1 , U. Pietsch 1 , D. Kurth 2 und H. Möhwald 2 1 University of Potsdam, Institute of Physics, Am Neuen Palais 10, 14469 Potsdam, Germany 2 MPI-KG Golm, Am Mühlenberg 1, 14476 Potsdam-Golm In the last years resonant magnetic X-ray reflectivity experiments (XMCD) become important for the investigation of molecular magnetism in thin films. In the present work we report a novel approach to affect spin crossover by introducing mechanical strain through an amphiphilic phase transition in a metallo-supramolecular polyelectrolyte-amphiphile complex (PAC). The investigated system consists of thin layers deposited in Y-conformation on a silicon substrate by means of Langmuir-Blodgett technique. It was observed by EXAFS, x-ray reflectivity and in-plane diffraction experiments that the structural phase transition in the amphiphilic mesophase is responsible for the distortion of the coordination geometry of the tightly coupled transition metal centres. Consequently, the energetic separation of the subsets of the iron d-orbitals changes and gives rise to spin crossover. Using temperature resolved SQUID and XMCD measurements we observe a diamagnetic to paramagnetic phase transition above room temperature which is connected to a structural phase transition between two liquid crystalline phases. [HOME] [E-Verhandlungen 2004] [Regensburg] [Fachverband O] [Sitzung O 28] [Autorenindex] 31 of 32 07.06.2009 22:14
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