Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 9: Micromagnetism/Computational Magnetics

MA 9.4: Vortrag

Montag, 25. Februar 2008, 17:30–17:45, H 1012

Influence of the Oersted field on the current-induced dynamics of nanodisks — •Attila Kakay, Riccardo Hertel, Ronald Lehndorff, Daniel Bürgler, and Claus Michael Schneider — Institut für Festkörperforschung IFF-9 "Elektronische Eigenschaften", Forschungszentrum Jülich, GmbH, D-52425 Jülich, Deutschland

Stationary oscillations of the magnetization in nanopillars with characteristic frequencies in the GHz range can be induced by a spin-polarized dc current. The frequency of these oscillators is tunable by changing the current value or other external parameters. Experimental research shows that in some cases the frequency increases with increasing current density, an effect known as blue-shift. This blue-shift effect has been studied both experimentally and numerically. In the commonly used macrospin model, where the exchange energy is neglected, this blue-shift is assigned to out-of-plane precessional modes of the magnetization. Our full-scale micromagnetic simulation provides a different explanation for the blue-shift, showing that it originates from the Oersted field. The mode profiles of the characteristic magnetization dynamics around 8 GHz are extracted using spatial Fourier filtering. In the presence of the Oersted field the mode profile is changing with increasing current in such way, that the distance between the oscillating regions decreases, which leads to the increase of the oscillating frequency, thereby explaining the observed blue-shift. Good quantitaive agreement is obtained between simulations and experiment regarding both the main frequency and its shift.