FREE-ELECTRON POLARIZATION IN A FERRO-PARAMAGNET THIN BILAYER

We show that the spin polarization of free electrons in metallic ferro-paramagnet planar bilayer gives rise to antiferromagnetic coupling, in thicknesses of less than 100 layers. Physically, as a consequence of the strong quantization of the perpendicular component of the wave vector, the difference in energy of the unperturbated electronic levels mixed by the one-dimensional magnetic Hamiltonian, is much larger than the perturbation energy produced by the molecular field of the ferromagnet. Due to the sharp edge of the Fermi level the antiferromagnetic coupling strength is modulated by typical RKKY oscillations, in spite of this the long range polarization is never ferromagnetic.