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DS: Dünne Schichten
DS 22: Magnetische Schichten I
DS 22.4: Talk
Thursday, March 20, 1997, 11:00–11:15, PC 7
Morphology and Curie-temperature changes upon annealing of Co/W(110) studied by STM and ac-MOKE — •T. Günther, A. Mühlig, A. Bauer, G. Kaindl, M. Farle, and K. Baberschke — Institut f"ur Experimentalphysik, Freie Universit"at Berlin, Arnimallee 14, D-14195 Berlin
Growth and magnetism of room-temperature grown and subsequently annealed Co/ W(110) films up to 4 monolayers (ML) Co are studied by STM and ac-MOKE. For the as-grown films, the STM images reveal nearly layer-by-layer growth. Long-range magnetic order with Curie temperatures Tc > 150 K is observed above 1.5 ML Co. Annealing of < 3 ML thick Co films at > 440 K leads to a considerable decrease of Tc. For thicker films, however, an increase of Tc is observed upon annealing. These changes in Tc are correlated to morphology transformations: Thin Co films break up into disconnected islands on top of a stable Co monolayer (Stranski-Krastanov growth mode). This STM result suggests that the decrease of Tc is possibly due to a lateral finite-size effect. On the other hand, gentle annealing of thicker Co films leads to a significant surface flattening. At higher annealing temperatures small holes are observed that grow until a network-like structure of interconnected Co islands is formed. Eventually, the bonds between the islands break up and quasi 3-dimensional (3D) crystallites of considerable size (several 1000 Å in diameter) are observed. The continous transformation to 3D-structures explains the increase in Tc.