Abstract
We describe a new "complete" spin-polarized electron energy loss spectrometer comprising a spin-polarized primary electron source, an imaging electron analyzer, and a spin analyzer of the "spin-polarizing mirror" type. Unlike previous instruments, we have a high momentum resolution of less than 0.04 Å(-1), at an energy resolution of 90-130 meV. Unlike all previous studies which reported rather broad featureless data in both energy and angle dependence, we find richly structured spectra depending sensitively on small changes of the primary energy, the kinetic energy after scattering, and of the angle of incidence. The key factor is the momentum resolution.
Highlights
Spin-polarized electron energy loss spectroscopy (SPEELS) is a powerful tool to study electron excitation dynamics in ferromagnetic and paramagnetic solids
With respect to itinerant systems there were some deficiencies found worldwide. They were nicely summarized by Komesu et al.[10] in 2006: “In general, these studies report rather broad featureless data in both energy and angle dependence, and this has been attributed to non-conservation of the perpendicular momentum component in the scattering process,[8] nonuniform exchange splitting throughout the Brillouin zone (BZ),[11] and umklapp scattering together with the structure of interband densities of Stoner states in the material.”[12]
Every SPEELS experiment starts with a polarized electron source (Fig. 1)
Summary
Spin-polarized electron energy loss spectroscopy (SPEELS) is a powerful tool to study electron excitation dynamics in ferromagnetic and paramagnetic solids. This potential was pointed out in theory,[1,2,3] and experiment[4,5] in the middle 1980s already. This may occur in two ways: first, an exchange process within the same spin system, and second a purely dipole transition, i.e., a process where the excitation is independent of the electron spin These contribute both to the non-flip channels, but their proportion cannot be separated experimentally, only by theory. In the remainder of the paper, we describe the electronoptical components of our new instrument and conclude with some examples of its performance
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