Dresden 2009 – scientific programme

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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 40.89: Poster

Friday, March 27, 2009, 11:00–14:00, P1A

Microwave-Assisted Magnetization Reversal in Ni₈₀Fe₂₀ Nanowires: Reduced Critical Fields in Arrays with sub 100 nm Spacing — •Jesco Topp¹, Stefan Mendach¹, Detlef Heitmann¹, and Dirk Grundler² — ¹Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, 20355 Hamburg, Germany — ²Physik-Department E10, Technische Universität München, James-Franck-Straße, 84747 Garching b. München, Germany

We studied microwave-assisted switching (MAS) in densely packed arrays of Ni₈₀Fe₂₀ nanowires. We used electron-beam lithography and lift-off processing to prepare arrays of 300 nm wide and 20 nm thick ferromagnetic nanowires with an edge-to-edge spacing of 90 nm. To study MAS the nanomagnets were irradiated with a microwave (rf) of fixed frequency and power and the linear eigenmode spectrum was used to probe the magnetization configuration inside the array.

We observe microwave-assisted switching for rf fields of less than 2 mT, a factor 3 lower than reported previously for individual nanowires of similiar dimensions. The phase-diagram of the switching efficiency is a complex function of rf amplitude and frequency. The switching process is most efficient at frequencies below linear eigenfrequency, which we attribute to the non-linear nature of the precession that leads to the magnetization reversal. For higher rf amplitude the regime of MAS is severely broadened by several GHz. Under optimal conditions the switching field can be reduced by more than 50%.

This work is supported by the DFG via "SFB 668" and the "Nanosystems Initiative Munich" (NIM).