Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 40: Poster II: Bio- and Molecular Magnetism (1-9); Magnetic Coupling Phenomena/Exchange Bias (10-15); Magnetic Particlicles and Clusters (16-29); Micro and Nanostructured Magnetic Materials (30-51); Multiferroics (52-64); Spin Injection in Heterostructures (65-67); Spin-Dyn./Spin-Torque (68-93); Spindependent Transport (94-108)

MA 40.76: Poster

Freitag, 27. März 2009, 11:00–14:00, P1A

Trajectory imaging of current-induced gyrotropic vortex motions — •Martin Müller, Christian Dietrich, Christian Back, Dieter Weiss, and Josef Zweck — Institut für Experimentelle und Angewandte Physik der Universität Regensburg, Germany

Transmission Electron Microscopy (TEM) can be used to study current induced excitations in low dimensional magnetic systems. Lorentz microscopy, a special operating mode with switched-off objective lens, using a long focal length lens instead, yields information about domain wall structures and/or the vortex position of magnetic disk samples. In this work we investigate magnetic specimens with different geometries (Landau structures in thin-film square elements/vortex structures in disks) and lateral dimensions in the micrometer range. It is possible to excite the gyrotropic eigenmode of the vortex structure by a spin-polarized ac current with frequencies in the range between 40 to 400 MHz. Lorentz microscopy enables us to image the trajectory of the vortex motion. We demonstrate that the resonantly excited vortex core has a circular trajectory whereas in off-resonance the motion of the vortex core is elliptical as predicted by analytical calculations[1]. The shape and the size of the trajectory and its frequency distribution depends on the ratio of spin transfer torque and Oersted field and therefore on the spin polarization of Permalloy.

Modifications in the magnetic specimen, such as an artificially created hole or other defects have been investigated and show a different vortex motion.

[1] Ki-Suk Lee, Sang-Koog Kim, Phys. Rev. B 78, 014405 (2008)