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MA: Fachverband Magnetismus

MA 11: Focus: Progress in Spin-Polarized Electron Spectroscopies

MA 11.1: Hauptvortrag

Montag, 16. März 2015, 15:00–15:45, EB 301

Acoustic und standing spin wave modes in ultra-thin 3d metal films — •Harald Ibach — Peter Grünberg Institute, Research Center Jülich, Germany

The spin wave spectrum of well-ordered ferromagnetic N-layer films consists of N modes with zero to N-1 nodes inside the film. The energy of these spin waves as function of the wave vector parallel to the surface may be studied by using inelastic scattering of low-energy electrons. Because of low energy resolution (FWHM=20-40meV) early work on cobalt and iron films had to focus on the high-energy and high wave vector regime q|| > 3nm-1 where the damping of the modes due to Stoner excitations is extremely large. For fcc cobalt films this has led to the erroneous interpretation that (i) electrons interact primarily with the surface mode of the film, that (ii) the surface mode is the lowest energy mode and (iii) that the dispersion of that mode is well described by a simple nearest-neighbor Heisenberg model with a single, layer-independent exchange coupling constant. With improved electron spectrometers featuring 3meV resolution we are now in the position to study the low momentum regime q|| < 3nm-1 where the spectrum consists of a series of separate, well-defined spin wave peaks. The study of these spin waves as function of the film thickness reveals that the exchange coupling constants near surface and interface differ substantially from those in the interior of the film. Spin wave spectroscopy has thus become a tool to study the layer dependence of the exchange coupling.