Berlin 2012 – scientific programme

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MA: Fachverband Magnetismus

MA 47: Micro- and Nanostructured Magnetic Materials II

MA 47.3: Talk

Thursday, March 29, 2012, 17:45–18:00, EB 202

Anisotropic magnetoresistance in self-assembled antidot arrays — •Felix Häring, Ulf Wiedwald, Lorenz Lechner, and Paul Ziemann — Institute for Solid State Physics, Ulm University, Germany

Magnetic antidot arrays are prepared by colloidal lithography using size-reduced self-assembled polystyrene (PS) colloids as templates for the subsequent deposition of magnetic thin films. After removal of PS spheres including magnetic caps we obtain hexagonally ordered Fe and FeNi antidot films (thickness typically 20 nm). Based on initially 200 nm PS spheres the antidot diameter is varied in the range 30-180 nm and changes of the hysteresis are examined and compared to a continuous film. We observe strongly increased coercive fields due to huge local shape anisotropy. In-plane anisotropic magnetoresistance (AMR) proofs that magnetization reversal and AMR amplitude heavily depend on the antidot diameter. Averaging over large areas of the array leads to loss of the expected 6-fold anisotropy. Constricting, however, the AMR measurements to highly ordered areas of antidots (about 2µm x 15 µm) by applying focused ion beam (FIB), we locally can study the magnetization reversal in next and next but one neighbor directions. In this way, observation of anisotropy with respect to the antidot lattice becomes feasible. Results are supported by micromagnetic simulations.