Electron Spin Polarization in Field Emission from EuS-Coated Tungsten Tips

Field-emitted electrons from EuS-coated W tips cooled to below 21 K show spin polarization of up to (89 ± 7)%. The preferential direction of the magnetic moments of the electrons is parallel to the magnetization of the emitter. The high spin polarization is explained in terms of emission from spin-polarized $4f^7$ states of ferromagnetic EuS or in terms of emission assisted by interaction with these states.