SURFACE AND 2D MAGNETISM WITH SPIN-POLARIZED CASCADE ELECTRONS

The probing depth lambda of low energy cascade electrons in transition metals (TM) is dominated by scattering into the unoccupied d-orbitals. Thus lambda for electrons within 5-10 eV from the Fermi level varies from 1 monolayer in the early TM such as Gd to 6 monolayers in the late TM(Ni). The spin polarization P(c) of the cascade electrons is due to the spin polarization P0 of the 3d-electrons plus an additional polarization generated in the process of cascade formation by scattering into the spin polarized holes of the 3d-states. The enhancement f = P(c)/P0 is small with the early TM but large with the late TM. Nevertheless, P(c) is proportional to the magnetization and therefore represents an ideal tool to observe magnetism at surfaces and in nanoscale magnetic structures. Very small exchange couplings of ferromagnets across nonmagnetic spacer layers can be measured if one of the ferromagnets is ultrathin and acts as a giant spin molecule without decaying into domains. Recent applications include the investigation of the exchange coupling across semiconducting spacer layers.