Regensburg 2007 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 26: Exchange Bias

MA 26.1: Vortrag

Donnerstag, 29. März 2007, 15:15–15:30, H10

Anisotropy and interlayer exchange coupling in thin magnetic films: beyond the Landau-Lifshitz evaluation of spin wave spectra — •Stephan Schwieger¹, Jochen Kienert², Fritz Körmann², and Wolfgang Nolting² — ¹Technische Universität Ilmenau, Theoretische Physik I, Postfach 10 05 65, 98684 Ilmenau, Germany — ²Festkörpertheorie, Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany

We present a general theory to determine the temperature-dependent magnetic anisotropies and interlayer exchange coupling in thin films from experiments probing collective spin excitations. Unlike the classical evalutation based on the Landau-Lifshitz equations our approach, by using the quantum Heisenberg model, considers self-consistently the effects of thermally activated spin waves. The close correspondence to the Landau-Lifshitz formulas for T→0 is demonstrated and the benefits of the theory for T>0 are worked out.

We show results on the magnetic reorientation transition due to a Cu cap layer in thin Ni films. For thin Ni and Co films we derived the T-dependence of the lattice and shape anisotropies. We finally discuss the evaluation of FMR experiments on exchange coupled Ni/Cu/Co trilayer systems. Here, for the first time, it was possible to separate quantitatively the two main sources of the temperature dependence of IEC, namely magnetic excitations and spacer layer effects.

We propose our method as a general tool to properly include finite temperature in the evaluation of anisotropy effects and IEC in experiments yielding spin wave spectra.