Paramagnetic Sheet at the Surface of the Heisenberg Ferromagnet EuO

Measurements of the spin polarization of photoelectrons from (100) surfaces of "pure" and doped EuO monocrystals reveal a paramagnetic surface sheet existing at temperatures far below the Curie temperature of the bulk. The extra electrons that are introduced on doping produce an increase of the molecular field in the surface. ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{O}$ crystals exhibit the highest degree of spin polarization (\ensuremath{\sim} 80%) observed in a photoemission experiment so far.

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