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Berlin 2005 – scientific programme

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MA: Magnetismus

MA 32: Mikro- und nanostrukturierte magn. Materialien II

MA 32.4: Talk

Wednesday, March 9, 2005, 11:45–12:00, TU H1028

Magnetic frustration in coupled ferromagnetic ring structures — •Volker Rose1, Harald Ibach1, Vitali Metlushko2, Seok-Hwan Chung3, Axel Hoffmann3, and Sam D. Bader31Forschungszentrum Jülich (ISG3), Germany — 2University of Illinois, Chicago, USA — 3Argonne National Laboratory (MSD), USA

It is well known that patterned soft magnetic ring structures can exhibit a magnetic vortex state. When two rings interact, i.e., through direct contact, then it is expected that the vortex states have opposite chiralities. Thus, if three rings are interacting there is an obvious frustration between the magnetic states. We have fabricated isolated and contiguous arrays of rings using e-beam lithography and lift-off, with diameters of 1-4 µm and ring widths of 0.2-1.8 µm made of permalloy thin films with a thickness of 15 nm. Their field dependent magnetization was investigated with magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) accompanied by micromagnetic simulations. Generally, in the case of isolated rings the magnetization predominately follows the circumference resulting in a flux-close vortex state. In case of a three ring structure two transitions are observed. One from a high-magnetic-moment state obtained after relaxing the field from saturation to the low-magnetic-moment state, indicating the magnetic frustration of one ring in presence of two rings in vortex state. The second transition belongs to the reverse high-magnetic-moment state. Work at ANL was supported by US DOE-BUS

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