Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 7: Spin-Dynamics/ Spin-Torque II
MA 7.13: Vortrag
Montag, 23. März 2009, 18:30–18:45, HSZ 04
Spin wave mode spectra of continuous and structured amorphous CoFeB films — •Henning Ulrichs, Jakob Walowski, Andreas Mann, Benjamin Lenk, Gerrit Eilers, and Markus Münzenberg — I. Physikalisches Institut, Universität Göttingen
Magnetization dynamics within the GHz-range in amorphous CoFeB thin-films are investigated using all optical pump probe experiments. After a fs-laser pulse excites the film, a second time delayed pulse is utilized to record the time dependent magnetization curve M(t) exploiting the time-resolved magneto-optical Kerr effect (TRMOKE). As an experimental variable a bias magnetic field 0mT≤µ0H ≤ 150mT in an angle to the samples surface between 0∘ and 30∘ is applied. From Fourier transformations mode spectra ω(H) are obtained. By comparison with theoretical dispersion curves different spin wave modes are identified. In the thinnest films (5nm to 25nm) only uniform precession is found. From the magnetization curves of the 25nm sample a very low Landau-Lifshitz-Gilbert damping factor of α ≈0.006 is extracted. For thicker films (50nm to 225nm) also Damon-Eshbach modes and perpendicular standing spin waves can be seen. In a second step we structured the surface of a 125nm CoFeB film with a focused ion beam. Two-dimensional cubic lattices of holes having a diameter of 5µm and a lattice constant between 15 and 23µm were fabricated. The distances were chosen close to the wave length of the propagating DE modes. The mode spectra of the structured regions are significantly altered, indicating Blochstates of DE waves forming due to the periodic potential. Research is supported by DFG Schwerpunkt SPP 1133.