Spin dynamics - experimental setup

We have shown that high wave-vector magnons can be excited and probed by spin-polarized electron energy loss spectroscopy (SPEELS) [1-3]. Our specially developed spectrometer is schematically shown in Fig. 1. A spin-polarized monochromatic electron beam, created by a strained GaAs-photocathode, is scattered from the sample at a given scattering geometry. The scattered electrons are analyzed with respect to their energy and wave-vector. The experiments are performed for two orientations of the incoming electron spin (parallel and antiparallel to the sample magnetization). Magnons are excited in an exchange scattering process. The conservation of the total angular momentum during the scattering process prohibits the magnon excitation for incoming electrons with a spin polarization antiparallel to the sample magnetization. Hence, only electrons of minority spin character can excite magnons. The electrons of majority spin character can consequently annihilate thermally excited magnons and gain energy [4].

Fig. 1: A schematic illustration of our high-performance SPEEL-spectrometer and the scattering geometry in our SPEELS experiments.