Generation of a spin-polarized electron beam by multipole magnetic fields

• Theory of generating spin-polarized electron beams.
• Interacting electron vortex beams with space-variant magnetic fields.
• Bohr–Pauli impossibility of generating spin-polarized free electrons.

The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin–magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope.