Ferromagnetism of novel ultrathin films and multilayers: A study of Ru/C(0001) and Fe/Mn/Fe/Pd(100) using magneto-optic Kerr effect and spin-sensitive electron spectroscopies

The possibility of the existence of ferromagnetic order in Ru monolayers on the C(0001) graphite surface is studied using electron induced spin-polarized secondary electron emission (SPSEE). Below a surface Curie temperature of approximately 250K we find ferromagnetic order of the Ru monolayer. The growth mode of Ru on C(0001) is investigated by Auger electron spectroscopy (AES). We find, that the initial growth occurs laterally until a homogenous monolayer is formed. Our study provides the first observation of spontaneous, two-dimensional ferromagnetic order of a 4d transition element. To investigate the spin-polarization and domain pattern in ultrathin films and multilayers, we develop a novel technique: scanning ion microscopy with polarization analysis (SIMPA). A highly focused Ga$\sp+$-ion beam from a liquid metal ion source is moved over a sample to locally eject secondary electrons, whose spin-polarization is determined by using a medium energy Mott polarimeter. We show that the sputtering by the ion beam can be well controlled and utilized for nano-lithography and spin-resolved sputter depth profiling. We use SIMPA and the surface magneto-optic Kerr effect to study exchange coupling in Fe/Mn/Fe/Pd(100) multilayers. The intervening Mn layer is grown in a wedge shape ranging in thickness from 0 to 9 monolayers. Our results show that both Fe layers are coupled ferromagnetically for the entire Mn thickness range. Growth mode and structure are analyzed by AES and medium electron energy diffraction