Spin-Resolved Resonant Electron Energy-Loss Spectroscopy (SR-rEELS): Observation of Element- and Spin-Selective Bulk Plasmons.

We have developed spin-resolved resonant electron energy-loss spectroscopy (SR-rEELS) in the primary energy of 0.3--1.5 keV, which corresponds to the core excitations of $2p\to3d$ absorption of transition metals and $3d\to4f$ absorption of rare earths. Element-specific carrier and valence plasmons can be observed by using the resonance enhancement of core absorptions. Spin-resolved plasmons were also observed using a spin-polarized electron source from a GaAs/GaAsP strained superlattice photocathode. Furthermore, this primary energy corresponds to an electron penetration depth of 1 to 10 nm and thus provides bulk-sensitive EELS spectra. The methodology is expected to complement the element-selective observation of elementary excitations by resonant inelastic x-ray scattering and resonant photoelectron spectroscopy.