Low-energy spin-polarized two-electron spectroscopy: a powerful tool for studying exchange correlation and spin-orbit interaction on surfaces
Samarin, Sergey1; Artamonov, Oleg2; Sergeant, Antony1; Kirschner, Jurgen3; Williams, James1
1Australia;
2Russian Federation;
3Germany

The exchange correlations and spin-orbit interaction (SOI) play fundamental roles in itinerant ferromagnetism. Exchange correlations are responsible for a long range spin order and the SOI can create preferred crystalline directions for the spins. The study of the exchange and spin-orbit interactions and their interference is a fundamental issue in surface magnetism. We present here the spin-polarized two-electron spectroscopy-in-reflection, which has been proven to be a very efficient technique for studying the exchange correlation and spin-orbit interaction on magnetic surfaces and thin ferromagnetic films. The instrument consists of a spin-polarized electron source and main chamber containing the sample to be studied, as well as auxiliary facilities for the sample preparation and characterization. The spin source produces a transversally polarized electron beam with a polarization of 60 to 70 %, which is directed to the sample. Polarization of the beam is chosen to be perpendicular to the scattering plane. Two time-correlated electrons emitted from the sample surface upon an impact of a single incident electron are detected by two position-sensitive detectors using coincidence technique. We combined the coincidence technique with the time-of-flight electron energy analysis to measure momentum distributions of correlated electron pairs for various mutual orientations of the polarization of the electron beam and the magnetization of the sample. This set of measurements allows us to extract the information on exchange correlation and spin-orbit interaction from measured spectra. Energy- and momentum-conservation in the electron-electron scattering allows the valence electron involved into collision to be located in the energy-momentum space of the valence band of the sample. In this way the energy and momentum location of the exchange and SOI can be established. A few examples of the application of this technique for studying ferromagnetic surfaces are presented.
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